Memoire Online - The use of short-term solutions against grape sunburn within a context of climate change in the Médoc vineyard

MASTER'S THESIS
Presented in order to obtain the
MASTER 2 IN AGRICULTURAL ENGINEERING
MASTER 2 IN INTERNATIONAL MANAGEMENT

THE USE OF SHORT-TERM SOLUTIONS AGAINST GRAPE
SUNBURN WITHIN A CONTEXT OF CLIMATE CHANGE IN
THE MÉDOC VINEYARD

Abstract

Use of short-term solutions against grape sunburn within a context of climate change in the

Médoc vineyard

The present study experimentally investigated the effect of two short-term solutions against grape sunburn: the use of kaolin sprayings, and early defoliation. Grape sunburn stems from climate change and is the result of a combination of both environmental and cultural factors. By increasing the reflected part of solar radiation, kaolin sprayings can reduce sunburn by acting on plant physiology. On the other hand, by sun-exposing bunches of grapes in an early developmental stage, early defoliation aims to develop thicker berry skin and reduce sunburn sensitivity. The aim of this study is to verify the efficiency of both methods against sunburn on Cabernet Sauvignon grapevines. In order to quantify the results, microclimate of the cluster zone, sunburn symptoms, hydric stress and berry physicochemical characteristics were analyzed.

While kaolin significantly reduced leaf temperature, and defoliation increased polyphenols production, both modalities contributed to reduce berry sunburn symptoms by 86 to 90%. The main hypothesis of this study was thus validated. The effect of kaolin on water status was significant on one parcel and absent on another. Overall, neither kaolin nor early defoliation modalities impacted the chemical properties of the berries, while kaolin seemed to have improved the physical properties of the berries, being larger and heavier. All in all, both studied solutions seemed to have had little to no negative impact on berry quality. However, it would be interesting to continue the study and perform berry and wine tastings by modality to evaluate the organoleptic consequences.

Keywords: grape sunburn, kaolin, defoliation, wine, vine, physiology, global warming

Résumé

Utilisation de solutions à court terme contre l'échaudage de la vigne dans un contexte de changement climatique au sein du vignoble médocain

La présente étude explore expérimentalement les effets de deux solutions à court terme contre l'échaudage de la vigne : la pulvérisation de kaolin, et l'effeuillage précoce. L'échaudage découle du réchauffement climatique et est le résultat de la combinaison de facteurs à la fois environnementaux et culturaux. En augmentant la part de rayonnement solaire réfléchi, le kaolin réduit l'échaudage en agissant sur la physiologie de la plante. D'un autre côté, en exposant au soleil les grappes à un stade de développement précoce, l'effeuillage permet le développement d'une pellicule plus épaisse réduisant ainsi la sensibilité des grappes à l'échaudage. L'objectif de cette étude est de confirmer l'efficacité de ces deux méthodes contre l'échaudage de la vigne sur des parcelles de Cabernet Sauvignon. Afin de quantifier les résultats, le microclimat des grappes, les symptômes d'échaudage, le stress hydrique et les caractéristiques physicochimiques des baies ont été analysés.

Tandis que le kaolin réduit significativement la température des feuilles, et que l'effeuillage précoce augmente la production de polyphénols, les deux modalités ont contribué à la réduction des symptômes d'échaudage entre 86 et 90%. L'hypothèse principale de cette étude est donc validée. L'effet du kaolin sur l'état hydrique a été significatif sur une parcelle, et absent sur la seconde. En général, aucune des deux modalités n'a négativement impacté les propriétés chimiques des baies, tandis que le kaolin a amélioré les propriétés physiques des baies, les rendant plus lourdes et volumineuses. Globalement, les solutions étudiées n'ont peu ou pas impacté la qualité des baies produites. Toutefois, il serait intéressant de poursuivre cette étude afin d'effectuer des dégustations de baies et vin par modalité, pour évaluer les conséquences organoleptiques.

Mots clés : échaudage, kaolin, effeuillage, vin, vigne, physiologie, réchauffement climatique

Foremost, I would like to acknowledge and give my warmest thanks to my internship supervisor, Blandine DE ROUFFIGNAC, for offering me such an incredible opportunity at Château Margaux in the R&D team, which lead me to work on diverse exciting projects. Her comments and suggestions were very much appreciated for my redaction, as well as her constant cheerfulness and availability.

I would also like to thank Jérôme GODINEAU, R&D technician, for accompanying and guiding me during this internship, and for his incomparable sense of humor. His dedication and mentoring abilities made a huge difference.

I would like to express my sincere gratitude to my PURPAN internship tutor and advisor, Mr. DENUX Jean-Philippe for his patience, guidance, and availability throughout my research and redaction process. His advice helped me to write this thesis, and I could not have imagined having a better mentor.

I am grateful to Mrs. Nicola MIRC, my TSM internship tutor and advisor, for her unmatched dedication, and for enlightening me on this thesis, as for the unforgettable semester spent at TSM.

I wish to show my appreciation to Mr. Philippe BASCAULES and Mr. Sébastien VERGNE, respectively chief executive and operations director, for their interest in my research throughout this internship.

I owe a sense of gratitude to Mr. Julien CAZENAVE, vineyard manager, and Mr. Pierre MÜLLER, his deputy, for their availability, constant help, and suggestions on my study. Their knowledge has allowed me to make some important choices made for this study.

I thank profusely all the vineyard staff under the direction of the vineyard manager, for their kindness and constant motivation, making me feel welcomed in the company. Their co-operation was essential to complete kaolin sprayings.

In addition, I thank Mr. Philippe BERRIER, cellar master, and his team for their warm welcome and the sharing of their skills on traditional tasks.

I also thank the rest of the team of Château Margaux, from the office to the logistics team, for their compassion, caring and good mood.

I sincerely thank the MENTZELOPOULOS family, for welcoming me on their property, and giving me the chance to work in such incredible conditions.

I wish to extend my special thanks to my co-interns and roommates for their contribution and interest in my experimentation, as well as for all the good times shared together, contributing to the successful completion of my study.

Last but not the least, I would like to thank my friends and family, Timothé, and especially my parents Christel and Georges MILCAN, and my sisters Flora and Léa MILCAN, for the continuous support and interest throughout my academic trajectory and this thesis.

«The world must come together to confront climate change. There is little scientific dispute that if we do nothing, we will face more drought, famine and mass displacement that will fuel more conflict for

Introduction

Climate influences vine growth and development, as well as its production potential. The suitability of wine varieties for climates depends on different parameter values and can evolve with climate change.

Climate change can be defined as long term variations of temperatures and meteorological models (United Nations, 2022). It is a major turning point in the evolution of wine practices. For years, the agricultural industry - including the wine industry - has been trying to find ways to adapt their practices to climate change. Indeed, global warming participates in the raise of temperatures as well as the multiplication of the number of drought events resulting in thermic, radiative, and hydric stresses for grapevine. As a consequence, climate change has caused and is continuing to cause early wine grape harvests in France (Cook, Wolkovich 2016).

Moreover, global warming is held responsible for changing the flavor of French wine. This comes from a modification of the grape organoleptic profile due to the climate change, causing higher sugar levels, resulting in a higher alcoholic degree (Boquet, 2006).

Another direct consequence of global warming is grape sunburn. This phenomenon can be defined as a physiological disorder that affects the organoleptic as well as the visual properties of the grapes. Physiologically, the grape's appearance changes as it develops brown and necrotic spots. Consequently, it can significantly decrease yield and cause losses in terms of commercial value (Gambetta et al., 2021).

As the grape sunburning episodes have followed the intensity of drought episodes in the Bordeaux region, Château Margaux has repeatedly been affected and suffered from grape sunburn leading sometimes to moderate yield losses, justifying its will to find solutions. Indeed, they faced extreme canicular episodes in the last 20 years, such as in 2011, and more recently in 2018, 2019, 2020, and 2022. Consequently, the vineyard was filled with grape sunburn spots, resulting in yield losses.

The grape sunburn issue subsequent from climate change has been under study since 2020 at Château Margaux, with the objective of limiting its impact on the vineyard.

This study will focus on finding the most adapted strategy to reduce grape sunburn without affecting the oenological potential of the harvest. Scientific trials will be implemented on the major grape variety of the vineyard; Cabernet-Sauvignon.

In order to present this study and tackle the subject of grape sunburn, the Master's thesis will firstly introduce contextual elements. Then, the materials and methods used to conduct the trial will be presented and justified, before exposing and analyzing the results. Finally, results will be discussed, and propositions will be formulated for the study perspective.

1. Climate change and its impact on grape sunburn

1.1 Climate change at a large scale

At a large scale, climate change causes raise in temperatures, also known as global warming. It also induces more drought and less rain events (Eveno et al., 2016). Global warming can be defined as the average increase of air temperature near the surface of Earth over the past one to two centuries (E. Mann, Selin, 2022).

Climate change has so far caused the increase of the average world yearly temperature over the last century, affecting the growing conditions for grape producers.

Climate change at the viticultural scale can affect yield, quality and economic viability (Jones et al., 2005). Due to global warming, the phenological stages of grapevine will continue to be earlier in the second part of the 21^st century (Duchêne et al., 2010; Webb et al., 2007).

Harvest date is a good indicator for climate change. Indeed, a 10-day variation in harvest reflects a 1°C variation of the temperature received by grapevine over the growing season. Over the last 50 years, a 15 to 20 day difference was observed for harvest date in the French viticultural regions (Daux et al., 2007).

Additionally, climate change can impact the geographical repartition of grape varieties based on the evolution of climate indexes (Jones and Webb, 2010). In order to maintain a certain quality and yield of grapes, the easiest long-term solution is to change grape varieties.

Some studies based on different climate model simulations suggest that our planet's average temperature could rise between 1.1 and 5.4°C by 2100, compared to our actual climate (Herring, 2021). Consequently, this raise in temperatures is expected to only cause more yield losses.

1.2 Climate change at the scale of the Bordeaux vineyard

1.2.1 Global warming in Bordeaux constatation

In the Bordeaux region, according to Météo-France (Lafon, 2021), the average temperatures have raised by 1.2°C since the beginning of the century. Moreover, this tendency is accompanied by an increase in heat wave events, as well as a reduction in cold episodes. According to a comparison between different possible scenarios, global warming will increase, and the annual average temperature in Aquitaine will gain between 2 to 5 °C by the end of the century (Salles and Le Treut, 2017).

According to the Aquitaine Artelia report, global warming will keep increasing, and the annual average temperature in Aquitaine will gain +2.2°C by the end of the century (Artelia, 2015).

During the last 20 years, the Médoc vineyard has faced many canicular events happening during the summer. The frequency of those events is growing and has consequences on the grapevine physiology, affecting its photosynthesis process as well as its water resources.

The canicular events characteristics are evolving more rapidly under the influence of climate change, becoming more frequent, longer, and more intense since 2015 (Adélaïde and Chanel, 2021).

In the long-term, those temperatures are going to keep raising until it won't be possible to keep cultivating the same grape varieties. According to an article published by the Proceedings of the National Academy of Sciences, close to 86% of the Bordeaux grape production is set up to be wiped out by 2050 due to global warming (Hannah et al., 2013).

1.2.2 Consequences of climate change on the Bordeaux vineyard

The raise in temperatures will have a major effect on the development speed of grapevine and its phenological stages. For the last 20 years, global warming has affected grapevine production causing an early maturity date by 15 dates on average. Climate models predict the maturation date for Merlot variety in Bordeaux to be 40 days ahead by the end of the 21st century (Brisson and Levrault, 2010).

According to simulations done in the 2000's, there are no evidence that climate change will impact the yield of the Bordeaux vineyard (Garcia de Cortazar, 2006). However, grape quality might be impacted by temperature and sun radiation intensity growth, as well as a potential water deficit.

Climate change will also directly impact grapevine diseases as it will force the pests and pathogens to adapt, and in the worst scenario causing their multiplication (Thiery and Chuche, 2007).

As a consequence to the multiplication of intense heat events, the quality of the produced wines might be affected. It has been proven that they raise the potential alcohol, reduce the acidity, inhibit the anthocyanins synthesis, and therefore affect the color and aromas of the produced wines (Santos et al. 2020).

For now, those extreme temperatures can cause grape sunburn. As this phenomenon is rising in France, it is already very important in other winegrowing regions where the average yearly temperatures are way higher than in France. For example, in Australia, this phenomenon is very common and impacts each year 5 to 15% of the grape production, causing dramatic yield losses. In Chile, up to 40% of bunches can show sunburn damage in sensitive varieties like Muscat (Gambetta et al., 2021).

However, the economic consequences caused by grape sunburn can be important. Consequently, many winemaking companies all over the world are experimenting new potential solutions to diminish the grape sunburn problem.

2. State of the art of grape sunburn

2.1 Grape sunburn: definition, symptoms, and consequences

Grape sunburn can be defined as a physiological disorder affecting both the visual and organoleptic properties of grapes. Only the bunches of grapes exposed to the sun can be affected by sunburn. It is noticeable by the brown and necrotic spots on the grapes. Those spots alter the commercial value of the fruit, but can also in extreme cases significantly decrease the yield (Gambetta et al., 2021).

Symptoms associated with grape sunburn range from the appearance of brown spots on the epidermis of grapes to the entire desiccation of the berries (Suehiro et al., 2014). We can see on Figure 1, both types of sunburn intensity (brown spots on the left and berries desiccation on the right).

Sunburn damages the berry epidermal tissue at the epicuticular and epidermal level. At the epicuticular level, it degrades the structure of the skin waxes causing their degradation and allowing a higher skin permeability, resulting in the dehydration and visual change of the grapes (Bondada and Keller, 2012). At the epidermal level, it destroys chlorophyll - causing a slight discoloration of the grapes - and induces cell compartmentalization, exposing polyphenolic compounds to polyphenol oxidases. As a result, the oxidation of polyphenols leads to the browning of the skin. The browning of the skin is also caused by cell death in the epidermal layers of the exocarp in the skin of the grapes (Olivares-Soto et al., 2020).

Figure 1: Observed symptoms of low-intensity (left) and high-intensity (right) sunburn at Château Margaux in June 2022

Browning can strongly decrease the market value of the crop and cause significant losses in quality of wine grapes. Sunburn mostly affects the skin of the grapes with little to no effect on the pulp, apart from its possible dehydration. However, sunburn can cause uneven ripening of the grape. A study on Cabernet Sauvignon berries showed that temperatures above 30°C can overall flavonoid content, and in particular the anthocyanin concentration, leading to a decrease in anthocyanin concentration, affecting the wine color (Pastore et al., 2013).

Sunburn browning is known to be the result of a combination of both high light and high temperature on the sun-exposed side of the fruit (Schrader et al., 2009). However, other factors can influence the temperature as well as the sun exposure of the fruit during the vegetative period. Those factors were classified in two categories, based on their durability.

2.2 Medium to long term factors of grape sunburn

2.2.1 Temperature: the main cause of grape sunburn

Temperature can affect the plant and the fruit, as it is a major source of abiotic stress. Fruits possess an intracellular signaling mechanism that gets activated in response to heat (Gambetta et al., 2021). Thermal stress mainly targets the photosynthetic apparatus of the plant, causing its modification to adapt to heat. Those changes are usually reversible, unless the heat is excessive, in which case the photosystems can be severely and irreversibly damaged (Araújo et al., 2018).

When exposed to high temperatures, plants can be subject to an imbalance between their light energy absorption and usage. Consequently, the fruit's respiratory mechanisms are modified. Higher temperatures (> 30°C) cause higher levels of respiration that can result in the accumulation of Reactive Oxygen Species¹ (ROS) (Jiang et al., 2015).

Apart from altering the regulation of metabolic pathways, the accumulation of ROS can cause membrane destabilization, protein denaturation, and berry pericarp cell death. High temperatures can cause early cell death, and therefore sunburn (Bonada et al., 2013).

2.2.1.1 Temperature at different scales

Temperature at the regional scale (macroclimate) is a major component of the vineyard (mesoclimate) and fruiting zone (microclimate) temperatures. In order to qualify the climates of viticultural regions and their ability to implant certain grape varieties, climate indices were created.

¹ An unstable molecule type involved in normal metabolism reactions containing two unpaired electrons from dioxygen that can easily react with other molecules in a cell. An excess generation of ROS in plants' cells can react with its DNA and gene expression, ultimately resulting in cell death (Bayr, 2005).

The Winkler Index (WI) classifies regions based on the accumulation of heat summation units, by adding up temperatures above 10°C during the growing season. This index attributes growing degree-days (GDD) to regions during the growing season (Amerine and Winkler, 1944).

The Huglin Index (HI) uses the heliothermic potential, calculating the sum of the temperatures above 10°C from April to September (growing season). It varies from the WI as it takes a the latitude of the location in consideration as it affects the duration of the day, and is therefore more precise (Morata, 2018). The day length coefficient of Bordeaux is 1.04.

Viticultural climates were classified in six categories, based on the HI calculation, from very cool regions to very warm regions (Tonietto and Carbonneau, 2004).

Table 1: Viticultural climates classification based on the Huglin Index (Tonietto and Carbonneau, 2004; Liviu Mihai et al.,

According to the HI, Bordeaux's climate went from temperate between 1956 and 1986 (HI = 1814), to warm temperate between 1987 and 2017 (HI = 2125). Cabernet Sauvignon and Merlot, the principal grape varieties of Margaux, have an HI between 1500 and 2100, and were therefore more adapted to a cool to temperate climate, than to the current warm temperate climate (CNRS, 2020).

The fruiting zone temperature (microclimate) depends on the bunch exposure. Indeed, the unexposed berries microclimate tends to mimic the parcel's under shelter mesoclimate, and is close to the air temperature (Spayd et al., 2002). However, the fruiting zone temperature can be very variable in one vine stock as it is very precise. It can therefore be said that the microclimate of the fruiting zone temperature is primarily defined by the air temperature, then modulated by other factors such as solar radiation, wind or air humidity (Gambetta et al., 2021).

2.2.1.2 Air temperature and its impact on berry temperature

Berry temperature is a function of radiative heat transfer and air temperature. Both factors cannot be separated as the relationship between temperature and absorbed light is linear. Direct sun exposure increases fruit surface temperature by 12 to 15°C above air temperature on the berry's sun-exposed side. Fruit surface temperature can therefore vary depending on the bunch location in the canopy, as well as the level of solar exposure (Spayd et al., 2002).

The berry temperature can also be affected by the bunch compactness, berry size, wind velocity, and its color. Dark-colored berries exposed to the sun and under low wind conditions can be up to 15°C above air temperature, explaining why sunburn mainly occurs during the veraison² stage (Dry, 2009).

Sunburn is mainly observed when berry temperature is above 45°C due to a combination of low wind-velocity, high temperatures, and high light causing radiative heat transfer (Schrader et al., 2009).

2.2.2 Solar radiation

Solar radiation plays an essential role in mechanisms such as plant morphogenesis regulation and photosynthesis. It is one of the most important environmental factors as it represents both a source of energy and information that interact with the plant the most. Solar radiation is capable to raise the temperature of a surface using the energy issued by the sun (Smart and Sinclair, 1976). Consequently, solar radiation and temperature are closely linked variables.

In the vineyard, the solar radiation received by the grapevine can be declined in three components: the direct solar radiation, the diffuse radiation, and the reflected radiation (Riou et al., 1989). The direct radiation comes from the sun and is directly oriented towards the grapevine. Part of this radiation is diffused by gazes and vapor in the atmosphere, while another part can be reflected by the ground to create an albedo (Gutiérrez-Jurado and Vivoni, 2013).

- Ultraviolets (UV): UV-A (400-315 nm) and UV-B (315-280 nm) - Visible: 400-780 nm, including PAR³ (400-700 nm)

According to an article on UV irradiance, the intensity of the components of solar radiation depends on altitude, longitude, season, time of the day and cloud coverage (McKenzie et al., 2003).

Light can act as both a source of heat as well as a driver of photochemical and oxidative reactions for the berry. Photooxidation plays a major role in the appearance of sunburn browning symptoms. In well-shaded bunches in the field, neither sunburn necrosis nor sunburn browning can be observed, meaning that solar radiation is the major actor in the apparition of sunburn symptoms (Rustioni et al., 2014).

Scientifically speaking, light has an effect on berry sunburn as it promotes the production of chlorophyll and reactive oxygen species, both promotors of oxidative stress in the photosystems of the plant and the fruit. Sunburn development is mainly caused by two components of light: PAR and UV.

When highly exposed to PAR, NPQ⁴ increases in order to protect the photosystem of the plant. This process works temporarily, as when the PAR overexposure continues, the NPQ can be photo-inhibited, causing sunburn damages (Glenn and Yuri, 2013).

³ Photosynthetically Active Radiation, amount of light available for photosynthesis, and therefore needed for plant growth (Fondriest, 2010).

⁴ Non-photochemical quenching (NPQ) is a process that takes place in the photosynthetic membranes of plants and algae, in which excess absorbed light energy is dissipated into heat. This mechanism is employed by the plants to protect themselves from high light intensity (Ruban, 2016).

UV being a high-energy form of radiation, it can collapse membrane integrity, depending on the duration, dose, and wavelength of exposure. As previously said, sunburn is mainly caused by the combination of both light and temperature. However, in areas with relatively low average temperatures such as New Zealand and Chile, grape and apple sunburn is mainly due to their high UV index (Schrader et al., 2009).

Additionally, the interaction between PAR and UV can result in greater changes in fruit composition than when separated. Even if PAR plays a bigger role in the degradation of the berry's photosystems, this interaction plays an important part in the apparition of sunburn damage (Glenn and Yuri, 2013).

Finally, no studies have yet reported a potential influence of IR-radiation on the apparition and development of sunburn.

2.2.3 Combination of high temperature and solar radiation

Studies showed that grapevine sunburn that can be observed in vineyard mostly results from the combination of high light and high temperatures. When trying to induce sunburn in a greenhouse by exposing plants to high light intensity but at low-moderate temperatures, little to no damage was observed. However, when those temperatures were raised to 38°C, sunburn damage on Semillon berries was observed at low light intensities and was intensified at high light intensities (Hulands et al., 2014).

2.2.4 Wind and relative humidity

Fruits and leaves temperature is regulated by evapotranspiration, thanks to the heat relieved by water vaporization. Under windy conditions, berry transpiration is increased, and the sun-exposed berries are cooled down by forced convection. Consequently, high wind velocities diminish the appearance of grape sunburn.

When in contact with the plant, wind clears the air of humidity produced by the plant's transpiration, forcing the plant to continue to evaporate and cool down (Pereira et al., 1999). On a ripe berry, fruit surface temperature is on average 5°C lower when wind velocity increases from 0.5 to 2.0 m.s-1 (Smart and Sinclair, 1976).

Relative humidity also has an impact on grape sunburn as it reduces the plant's evapotranspiration, which increases the risks of grape sunburn (Gambetta et al., 2021).

2.3 Short term factors of grape sunburn

Vineyard floor management can contribute to sunburn development. Soil can increase the reflected radiation on grapevine (2.2.2) depending on its characteristics. Indeed, bare and light-colored soils reflect more light and heat than cultivated ones (Dry, 2009), resulting in a potential increase in grape temperature.

Implementing cover crops in the vineyards can reduce the reflected light but might also be a source of competition for water with vines. Replacing light-colored soils or competitive cover crops by dark-colored mulches can reduce both light reflection and water competition (Dry, 2009).

The soil composition also is an important factor as it plays a central role for vine physiology. It conditions the water status for the plant and contains mineral elements that are essential for plant growth. For example, the soil's nitrogen status highly impacts plant vigor proven to impact sunburn sensitivity (Chone et al., 2001) (2.3.3).

The grape variety and the rootstock choice are essential for the adaptation of the cultivar to the terroir. Grapevine cultivars express different abilities to tolerate light and heat stresses. Rustioni et al. (2015) conducted a study on 20 cultivars underlining the central role of radiation in berry sunburn injuries. This study put into light that the response of different cultivars to thermos-radiative stresses varies. The cultivars were then classified based on their radiation susceptibility.

The rootstock choice as well as the cultivar choice can modulate the plant's vigor, affecting the canopy's porosity. When the canopy has a higher porosity, the shading is lighter, increasing the bunches' exposition causing sunburn (Southey and Jooste, 1991).

The grapevine cultivar can also influence the plant's sensitivity to sunburn. To start with, anthocyanin-containing fruits reach higher temperatures than lacking anthocyanins due to a lower capacity to reflect radiation (Smart and Sinclair, 1976), explaining why red grape varieties are often more susceptible to sunburn than white grape varieties.

The cultivar's sunburn susceptibility also depends on the bunch morphology. A study put into light that the berries' size is positively correlated to its temperature, as large berries reach higher temperatures, and are therefore more exposed to sunburn than bunches with smaller berries (Smart and Sinclair, 1976).

By implementing varieties with higher Huglin Indexes into the vineyard, the sensitivity to grape sunburn should be reduced.

Plant vigor can be defined as an observed increase in plant height and density through time (Short and Woolfolk, 1956). Plant vigor impacts grape berries' volume and foliage porosity. Higher vigor also leads to higher vegetation height and canopy density, and therefore a higher degree of shading, allowing to reduce the temperature of the bunch microclimate by limiting the direct received radiation.

As a consequence, plant vigor also modifies grape berry composition by reducing its radiation-induced polyphenol production and increases its sunburn sensitivity (Smart, 1985).

Modifying plant vigor is difficult, nearly impossible. However, in order to mimic canopy density and a higher degree of shading, a solution could be shade netting.

Grape berry sunburn sensitivity varies according to the developmental stages. A study reported that the grape berry susceptibility increases as the bunches develop. The grape berry is less susceptible to sunburn at early developmental stages (Hulands et al., 2014). Sunburn damages can be observed on pre-véraison grapes but at a very low intensity. The highest damages can be observed later, during véraison (Hulands et al., 2014).

In contrast, other studies showed that the berries are supposed to be more susceptible to thermal stresses earlier in the season due to a higher ratio of photoprotective pigments to chlorophylls in the grape berries, that decreases during berry development (Düring and Davtyan, 2002).

However, during the early developmental stages, the plant's photoprotective mechanisms are at their highest due to a high chloroplast activity. This capacity decreases during the plant's development, causing higher sunburn sensitivity (Joubert et al., 2016).

Soil water status plays an essential role in determining the yield potential and quality of crops. Water status of grapevine in the field can be evaluated by measuring the predawn leaf water potential (Williams and Araujo, 2002).

By maintaining a balanced soil moisture in the root zone, plants can optimize their transpiration throughout the day, increasing the relative humidity of the bunch zone (Suat, 2019). Higher canopy transpiration also reduces the fruit surface temperature (Cook et al., 1964), reducing sunburn risk and contributing to sunburn protection.

Important hydric stress promotes the production of ROS by plants. As mentioned before (2.2.1), ROS accumulation weakens the berries and can lead to cell death. Drought stress can also lead to smaller canopies due to reduced vigor, reducing the shading, increasing bunch exposure, and consequently increasing potential sunburn damage (Gambetta et al., 2021).

Implementing irrigation systems into the vineyard could be a solution to reduce water stress.

2.3.6 Vineyard management practices and operations to modulate the sunburn risk 2.3.6.1 Vineyard operations

Vineyard management operations can directly influence the sunburn sensitivity of cultivars (Rustioni et al., 2015). The pruning system determines for example the density of the canopy, which affects the degree of interception of solar radiation by the bunches. In hot winegrowing regions where grapes suffer from sunburn, minimal pruning systems can be employed to offer shelter and protect them (Gambetta et al., 2021). Avoiding excessive pruning and leaf stripping could reduce sunburn by avoiding sudden exposure of the fruit to direct sunlight.

Trellis systems usually used in central Europe were designed to intensify fruit exposure but can consequently increase sunburn damage (Gambetta et al., 2021). However, other suitable alternative trellising systems reducing direct radiation exist, such as: high-wire cordon, head-training, pergola, Geneva double curtain, and closing Y-shaped trellis (Palliotti et al., 2014).

2.3.6.2 Row orientation

Row orientation is an important driver of grapevine sunburn. Still many vineyards are oriented North/South, an orientation known to equally distribute radiation on both sides. Yet, even when light is equally distributed, berry temperature highly differs between canopy sides. As the sun rises in the North-East during summer, the East facing side is sun-exposed during the cool morning hours, while the other side is sun-exposed during the high-temperature afternoons. As a result, the berries are exposed to significantly temperatures according to their exposition, leading to higher sunburn symptoms (Gambetta et al., 2021).

An experimentation at Château Margaux in 2020 brought to light the sunburn symptoms differences between parcels with different orientations. Indeed, other orientations than North/South have unequal light distribution between row sides but globally show lower bunch temperatures. It was found in this study that the most efficient row orientation in order to avoid grape sunburn is the North-East/South-West orientation (Porte, 2020).

2.4 Grape sunburn at Château Margaux

According to the vineyard manager (interview in Annex 2), Château Margaux has faced sunburn for every vintage with high temperatures, such as: 2003, 2005, 2011, 2018, 2020 and more recently 2022. Sunburn represents a significative threat for grapevine production at Château Margaux, as even small damages can cause yield losses, and consequently economical losses. Due to the yield losses

linked with sunburn, some parcels might stop entering the first wine final blend, and will be declassified, resulting in additional economical losses. Moreover, sunburn can reduce the wine quality due to berry degradation caused by sunburn.

Overall, grape sunburn is a physiological disorder causing berry degradation, whose intensity is exacerbated due to climate change. While depending on many short- and long-term factors, its development is mostly correlated to solar radiation and external temperature.

3. Strategic analysis of Château Margaux in a context of climate change 3.1 The business sector of Château Margaux

As it is known around the world, wine is an important part of France's cultural and culinary heritage. Wine was first introduced in France 600 years before Christ, and was quickly propagated through the country, until it became a part of French culture (FranceAgriMer, 2020).

For many centuries, grapevine cultivation was rich, until the phylloxera crisis in 1864. This microscopic aphid pest was accidently introduced on the French territory, causing the near disappearance of the integrity of the French vineyard. In order to solve this problem, every French vine was removed and replaced by grafted French plants on the aphid-resistant American vines. Since then, the integrity of the French vineyard have grafted plants (Berton, 2022).

The French winegrowing sector is spread on 66 departments, and represents nearly 750 000 hectares of agricultural land, which accounts for 10% of the world's agricultural surface dedicated to wine production (CNIV, 2019).

In 2019, France was the 2^nd producer of wine in the world - behind Italy - with an annual production of 4.2 billion of liters of wine, representing 17% of the world wine production (CNIV, 2019). The winegrowing sector is the second contributor in the trade balance - behind the aeronautical sector - with a turnover of 12.7 billion euros in 2019.

France is also the 2^nd biggest wine consuming country in the world - behind the United States of America - with an annual consumption of more than 3.5 billion of bottles consumed (CNIV 2019).

The Bordeaux region is known all over the world for its exceptional wines and its diversity of vineyards. With 115 223 hectares of vineyard in production in 2019, Gironde is the first French viticultural department in terms of land and incomes. It is also the department with the most land under quality signs, representing 26% of the viticultural land under the PDO label in France. So, viticulture is very prominent in this department, as almost half of the used agricultural land is occupied by grapevines in 90% of the municipalities in Gironde (Agreste Nouvelle-Aquitaine, 2020).

Regarding the value of its production, Gironde is at the second position, with a production estimated to 2 billion euros in 2018. This represents close to 80% of the total agricultural production value of the department, and 3% of the French agricultural production (Agreste Nouvelle-Aquitaine, 2020).

The Bordeaux vineyard is diverse and counts many prestigious wine chateaux. To differentiate them, a classification was implemented in 1855, for the 3^rd Paris Universal Exposition. The winemaking chateaux were ranked based on the quality of their wines, based on different criteria. The wines from the Bordeaux region are known and appreciated all over the world, creating market opportunities for wine producers.

As a result of the high wine competition in Gironde, the industry keeps evolving and adapting. More and more consumers are now looking to consume more responsively and to diminish their environmental impact, as do the wine producers. In this context, the wine industry in Bordeaux keeps improving its performances in terms of sustainable development. In 2019, more than 65% of the vineyards of Bordeaux were certified by an environmental approach. Among them, the most popular are organic and integrated viticulture (Terra Vitis, HVE3, ISO 14001, etc.) (CIVB, 2020).

Château Margaux is a first growth in the Médoc Classification of 1855 (« Premier Grand Cru Classé en 1855 »), located in Margaux.

Most of Château Margaux's vineyard is in the Margaux Protected Designation of Origin terroir. This terroir is part of the Médoc, one of the six biggest wine regions in Bordeaux, alongside the left-part of the Gironde estuary. The Margaux PDO is close to 1 490 hectares (Hachette, 2009) and is close to the Atlantic Ocean. Its position allows it to have an oceanic and temperate climate, with an average rainfall of 763.48 mm per year, based on the Margaux Sencrop weather station (average calculated between 1996 and 2015).

Figure 3: Map of the Bordeaux vineyard, and location of the Margaux appellation (red box) (CIVB, 2020)

As it can be observed on Figure 3, the Bordeaux vineyard is wildly spread in the Gironde department and is mainly composed by six winegrowing regions: Graves and Pessac-Léognan, Médoc, Entre-Deux-Mers, Libournais, Blayais-Bourgeais, Barsac and Sauternes (CIVB, 2020). Viticulture therefore is an important part of the Bordeaux region that generates a significant economic activity. From the grape-growing activity to the wine selling activity, this sector is represented in Gironde by not less than 7 555 establishments and 32 000 employees (Agreste Nouvelle-Aquitaine, 2020).

Château Margaux's terroir is diverse, with more than 60 different types of soil, represented in Annex 3.

The main challenge of Château Margaux is to have environmentally and humanly friendly practices while adapting to climate change. Their objective is to develop the company and their practices to keep producing quality grapes that express the terroir typicity.

In this context, the current vineyard management practices can be modified to implement climate change up to a certain point, as long as those practices do not affect berry and wine quality.

The vineyard of Château Margaux represents 262 total hectares of land, in which only 94 hectares are used for grape production. The other hectares are dedicated to forests and meadows, allowing the company to welcome cows and sheep. 82 hectares are located in the Margaux appellation (red varieties), whereas 12 hectares are located in the «Bordeaux Supérieur» appellation.

The vineyard is composed of different grape varieties. For the red wine, the Cabernet Sauvignon is the main variety, holding 52% of the vineyard. Then comes the Merlot in second position with 26% of the vineyard, followed by 7% of Petit Verdot, and 3% of Cabernet Franc. The white wine is entirely made out of Sauvignon Blanc, representing 13% of the vineyard.

Cabernet Sauvignon is preferred by the production team for its adaptability to the Médoc terroir. However, this variety, along with the rest of the vineyard, is subject to grape sunburn.

The parcels are distributed in blocks close to the Château. In total, the property counts 8 blocks of red grape varieties, and 1 block of white grape variety. The map of the vineyard's parcel blocks and grape varieties can be found in Annex 4.

The density of plantation is 10 000 plants per hectare (1m x 1m) for the Cabernet Sauvignon, Cabernet Franc and Petit Verdot, and 6 677 plants per hectare (1.5m x 1m) for the Merlot and Sauvignon Blanc. This density of plantation is kept by complantation⁵.

To combat grape worms, pheromone diffusers were integrated all over the vineyard causing sexual confusion and disrupt mating between male and female butterflies.

At the end of the year (December-March), the vine stocks are pruned using the Medocain method, the most popular pruning method in Bordeaux, for red grapes. This method consists of leaving each vine stock with one cane on both sides of the trunk (double Guyot), each carrying three buds and two spurs, allowing the cutter to continue working easily on the same vine stock the next year without its extension. The additional parts that aren't used are cut, and both canes are bent and attached to the carrying wire. For the white grapes, they use the simple Guyot pruning method (only one cane) with six buds and they alternate the sides for the spur. The cane is then also bent and attached to the carrying wire.

The plowing-down starts from the bud burst stage, followed by the mechanical weeding of the plots, using claws and blades. A second plowing-down takes place during the summer, when the soil under the vine stocks is covered in weeds. Grass covers in the rows are only kept for the Merlot parcels and on clay soils, all year long to better the soil bearing capacity. The property doesn't use herbicides and prefer the use of mechanical weeding methods.

When the plants are growing, different vine treatments are implemented. For the phytosanitary strategy, certified authorized organic products are used as much as possible. Most coverage treatments are done with copper and sulfur-based solutions during the vegetative period. However, the company doesn't want the organic certification, as they consider that copper treatment has its limits and can eventually

⁵ The action of planting new vine-stock where holes are present in the vineyard.

become toxic for their soils. Château Margaux are also experimenting new natural and biodegradable products less toxic than copper and sulfur, and are searching for alternative methods against those treatments, through scientific trials. In 2022, around 11 coverage treatments were done.

At the fruit set stage, the vines are trellised and trimmed. Shoot removal takes place in May, followed by thinning operations in July. Finally, harvests are done manually in 5kg crates brought to the sorting line before being processed. At the end of harvest, there is a hilling done to the plants with a ridging plough.

Consequences of climate change at the scale of Château Margaux are multifactorial. To start with, some lands are expected to be lost in the future due to the vineyard's proximity to the Gironde. Then, climate change will also impact the vineyard management strategies, as alternative solutions to reduce its consequences will have to be implemented to maintain grape quality (interview in Annex 2).

Experimentations are currently being conducted before implementing changes at the scale of the vineyard. Most vineyard management practices have been in place for hundreds of years, so the company wants to make sure that quality wouldn't be affected by new practices before applying solutions to the integrity of the vineyard.

Château Margaux has acquired some knowledge on their practices, vineyard and wine, which is essential for innovation. The main challenge that climate change has brought to the company is to adapt their vineyard management strategies without affecting their typicity, and while assuring at the same time to stay in the PDO.

In this context, they can consider changing the company's practices in the vineyard, up to a certain point. For example, a solution to face climate change might be to change the implanted grape variety based on the Huglin Index adapted varieties. However, this would affect the wine typicity, so it cannot be considered (Leeuwen and Darriet, 2016).

To adapt, one strategy is to delay the vineyard operations in order to defer the maturation date and overcome the consequences of global warming. For example, by performing late pruning (March), the budburst is delayed by a couple of days. Another possibility is to raise the trimming height of the canopy to produce more shade and reduce the temperature.

To overcome the potential water deficit, it can be considered to lower the plantation density to reduce soil water use. As the climate is oceanic, irrigation strategies should only be considered as a last resort.

Climate change will also cause the multiplication of climate events such as hailstorms and drought events. In Argentina, where hailstorms are frequent, anti-hail nets are used at a large scale in the vineyards (Loussert, 2017). Those type of nets can be very useful for the vineyard but are for now unauthorized by the PDO registry.

The property was bought in 1977 by André Mentzelopoulos. Corinne Mentzelopoulos, his daughter, is now the owner and CEO, since her father's death in 1980. The company has two offices: one in Margaux, and another one in Paris. The office in Paris is mainly dedicated to administration and accounting. The site in Margaux comprises: the production (vineyard management, cellar, maintenance, expeditions), the R&D department, IT, visits and external relations.

An organigram summarizing the organization of the company can be found in Annex 5.

Apart from affecting the agricultural management of companies, global warming also impacts, and will keep impacting, companies' global managerial strategies to consider this major change.

The objective of Château Margaux is to maintain their wine quality and typicity, what makes it emblematic. In order to deal with this climate change and maintain both the typicity and quality of their wines, Château Margaux try to find adaptation strategies. The R&D department is therefore very important for the company, at it is financed with the objective to find solutions to current problems, to build tomorrow's company.

What makes Château Margaux different from the other vineyards is their preoccupation about innovation and allocate money to research topics linked with climate change.

3.3 The wines produced by Château Margaux in a context of climate change

The red wines are produced under the Margaux PDO, while the white one is produced under the Bordeaux PDO. The wine that isn't selected for those four bottles is intended to produce two generic wines (one red and one white), sold in bulk.

Figure 4: Wines produced and sold by Château Margaux (Château Margaux, 2022)

270 000 bottles of red wine, and 10 000 bottles of white wine are produced each year. The most produced red wine is their first classified red wine, with 130 000 bottles produced each year.

The first wine of Château Margaux is known for its quality and typicity. Sensorially speaking, the wine is recognizable for its silky tannins, gustatory sweetness, elegance, floral aromas, etc. Those specific features are produced in a certain terroir and climate and cannot be reproduced in different conditions. Undoubtedly, climate change will affect those features, affecting the wine typicity.

The wines produced by Château Margaux are known all over the world for their exceptional taste and quality. In order to understand the effects of global warming on Château Margaux's products, the key factors that condition the quality of their wines need to be defined first.

According to the vineyard manager (interview in Annex 2), the typicity of Château Margaux's wines comes from their terroir. With more than 60 different types of soil units and 3 types of terrasses, Château

Margaux has the potential to produce a more complex blend than its neighbors, enriching the wines' profiles. The soil map of the parcels can be found in Annex 3.

Grape quality is a result of every action in the vineyard. At Château Margaux, all of the tasks are handmade for a higher precision. Every vineyard worker takes care of specific parcels so that they become responsible and precautious of their work.

Pedological studies are done frequently in parcels to identify their terroir specificities and decide in which type of wine the parcel will go. Also, the company keeps records of the parcels' history specifying which type of wine each of them has produced throughout the years. Thanks to that information, and based on the type of vintage, decisions are taken each year regarding the blend.

The vinification process also interferes with wine quality, as the operations are directed to optimize the berry quality through analytical data and tastings.

Climate change will directly impact the wines of Château Margaux. According to the vineyard manager (interview in Annex 2), climate change will impact the quality of the produced wines, as the berries will taste differently due to higher sun exposure.

Climate change might also cause differences in berry taste due to other factors such as drought or even intense rainfall. Château Margaux being renowned in the wine industry for its wine quality and typicity, implementing new practices to reduce the effects of climate change on their vineyard might change the wines profiles and therefore impact the company's popularity.

4. Adaptation strategies to climate change

Climate change can affect the growing conditions of grapevine, and therefore impact the grape yield and quality. In order to overcome those effects, some adaptation strategies can be implemented at the scale of the vineyard. Those solutions can be either short-term or long-term oriented, based on their effectiveness. This part will present different adaptation solutions against climate change.

Some solutions are rather long-term oriented, since grapevine is a perennial plant and cannot be replanted easily and quickly.

As seen earlier in this report (2.3.6.2), row orientation is an important driver of grapevine sunburn. Reorienting the vineyard to avoid grape sunburn can be efficient in terms of yield losses reduction. Based on a conducted study at Château Margaux (Porte, 2020), the best orientation to avoid grape sunburn is the North-East/South-West orientation.

Consequently, changing the row orientation of every parcel would be an ideal solution to diminish grape sunburn. However, this solution is long-term oriented and hardly applicable to perennial plants such as grapevine. Moreover, not every parcel in the vineyard can be reoriented because of practical and geographical reasons, forcing Château Margaux to find both short-term and long-term solutions.

Château Margaux historically implants specific grape varieties in their vineyard, as they produce a certain wine typicity when implemented on their terroir. However, some grape varieties have the capacity to resist to higher temperatures than others, making them more adapted to certain types of climates (2.3.2).

As we can expect that climate change will cause a raise in temperatures, implementing new temperature-resistant grape varieties into the vineyard could represent a potential solution against grape sunburn. However, by doing so, it would affect the wine profile and quality, and therefore change the typicity of the renowned Château Margaux.

Some solutions are short-term oriented due to the fact that they aren't considered as answers to grape sunburn, but as preventive ways to reduce yield and quality losses.

Climate change could impact the water supply for grapevine production. Irrigation based on weather forecasts and water potential measures could be used to meet grapevine's water requirements. If the plant's water needs are met before important heat waves, it could avoid or reduce grape sunburn (Lal and Sahu, 2017).

This solution is already used in other wine regions in the world, where temperatures during the growing season are higher, such as in New Zealand or in the United States of America. However, irrigation isn't yet authorized by the PDO registry, and therefore cannot be implemented at the scale of the vineyard.

Shade netting consists of applying a net at the scale of the vineyard to provide protection from high solar radiation. This solution seems ideal to reduce the radiation received directly by the berries and can also consequently reduce their temperature. Direct sunlight being the primary cause of sunburn (Lal and Sahu, 2017), shade netting could effectively and significantly reduce the damages linked with sunburn.

However, just like irrigation, shade netting isn't authorized by the PDO registry, and cannot be implemented in the vineyard yet.

4.2.3 Kaolin: a preventive solution against different radiative and thermic stresses During summer days, Vitis vinifera photosynthetic activity decreases due to stomatal and non-stomatal limitations (Chaves et al., 1987). In order to mitigate those effects caused by extreme temperatures and high irradiance, organic compounds can be applied to the canopy to increase grapevine physiology, productivity and quality (Ou et al., 2010).

When maturing, the Cabernet Sauvignon grape berries change color. As a consequence, they reflect less light and absorb more, resulting in the raise of temperature of the berry and leading to sunburn vulnerability. To reduce the part of absorbed radiation by the berry, some studies suggest that we can apply a kaolin-based particle film to the canopy.

Kaolin is a white clay made out of aluminum phyllosilicate that, when mixed in water and adjuvant and sprayed on the canopy, is capable of leaving a thin white layer on the leaves and fruits allowing a higher light reflectance capacity (Yazici and Kaynak, 2009). Kaolin increases the reflection of incident radiation on leaves and bunches, and consequently lowers their temperatures, reducing the plant's thermic stress (Brillante et al., 2016).

A study evaluated that kaolin treated plants reflect between 26 to 155% more UV and PAR throughout the growing season of the grapevine than the non-kaolin-treated plants (Lobos et al., 2015). As UV and PAR are the main two components of light that cause sunburn development (2.2.2), their reflection should lower the plant's sensitivity to sunburn. Thanks to this reflective action, kaolin treatment can improve the plant's water conditions, and diminishes its hydric stress (Glenn and Puterka, 2010; Glenn et al., 2010).

Moreover, another study demonstrated that kaolin spraying on leaves can increase the photosynthetic activity of the berries growing under low light conditions inside the canopy due to higher reflection of PAR in the inner zones (Garrido et al., 2019).

The grape berries are partially protected from light and heat stress thanks to their epicuticular waxes. The waxes protect the berries from PAR and UV radiation by reflection, absorption and scattering mechanisms, allowing to reduce the exposure levels in the tissues of the berry. However, the epicuticular wax layer of the berries' capacity to scatter light depends on parameters such as the berry's size and the wax crystals distribution and orientation. There are two types of wax crystals: plate-like and amorphous. The plate-like wax crystals have a tendency to scatter a higher proportion of light than amorphous waxes (Jenks and Ashworth, 2010).

According to a study, plate-like wax crystals prevail in light-exposed grape berries, while amorphous wax crystals prevail in grape berries grown in the shade of the canopy (Muganu et al., 2011). Sunburn causes the degradation of the plate-like wax crystalline structure into amorphous masses, leading to higher levels of dehydration and water permeability of the berry (Greer et al., 2006; Bondada and Keller, 2012).

Other studies evaluated that sun-exposed berries possess thicker cell walls and an epicuticular wax layer than the shaded ones, thanks to their higher capacity to reflect light (Muganu et al., 2011; Rosenquist and Morrison, 1989; Jenks and Ashworth, 1999; Verdenal et al., 2019), proving that early berry sun-exposure can be beneficial against sunburn.

Accordingly to the fact that sun-exposed berries retain more plate-like wax crystals, we can conclude that exposing berries to sun under normal conditions leads to a higher production of plate-like wax crystals, and therefore protects the berries from sunburn by scattering a higher proportion of light.

Besides, the exposure of grape berries to sunlight increases their levels of sugars, anthocyanins and phenolics. Early leaf removal on the canopy allows higher exposure of the berries, and therefore induces their skin thickening, providing more epidermal layers destined to the storage of anthocyanin compounds for protection against sunburn. The increase in sunlight exposure of berries on early defoliated vines also induces the expression of cell wall metabolism, resulting in an increase in berry skin thickness (Pastore et al., 2013).

Consequently, as a response to light exposure, the cuticle of the exposed berries synthetizes and accumulates higher levels of polyphenols. Moreover, light-exposed berries possess a thicker epidermis than shaded berries, due to their increased polyphenols accumulation (Pastore et al., 2013; Solovchenko, 2010), providing protection for the berry against sunburn.

In order to expose the berries to sun rays progressively, we can perform early defoliation on the canopy at a moderate intensity, and on the morning sun-exposed side of the canopy, so that the sun rays remain moderate.

All the presented solutions aim to reduce the effects of climate change. However, two of them are focused on reducing the damages linked with grape sunburn: kaolin and early defoliation. As we decided to focus on the sunburn issue in this report, only those two solutions will be explored.

5. Problem and hypotheses

As mentioned earlier in this report, climate change is causing the recent multiplication of both drought and canicular events during summer in the Médoc region. Therefore, more and more grape sunburn has been observed, resulting in yield and economic losses. Global warming has caused a modification of the typical Médoc climate, forcing the producers to change their production habits. Producers indeed have the choice between choosing to change the way they produce their wines (change the grape variety for example) at the risk of producing wines with different organoleptic profiles, or to adapt to climate change by finding short term solutions to reduce sunburn.

Château Margaux being an iconic figure of the Médoc vineyard, and being known worldwide for its exceptional wines, it seems impossible for them to entirely change their wines profiles. Their only option is to find solutions to adapt at a production level, without affecting their grapes and wines quality.

In the long-term, they plan on reorienting their plots of land to reduce the grapes exposure to the sun on the afternoon. Before being able to do so, they need to find short-term solutions.

The objective of this study is to find short-term solutions to adapt and reduce the effects and consequences of grape sunburn on Château Margaux's wine production.

What short-term solutions can be applied to a Médoc vineyard to significantly reduce its losses linked with grape sunburn?

- Will the spraying of a kaolin-based solution on the grapevine allow to protect the vineyard against grape sunburn?

- Is there a significant difference between the tested methods? Which solution seems to be the most efficient against grape sunburn?

- Will berry quality be impacted by kaolin treatments and early canopy defoliation?

- What effects the implementation of these potential solutions will have on the current vineyard management strategy?

The mission of this report will be to prove the efficacity of two different methods to potentially reduce grape sunburn. Both methods will be tested in the vineyard to evaluate their effect on grape sunburn, for the 2022 vintage.

It can be proposed to test both the use of a kaolin-based solution, as well as the use of early moderate plant defoliation before berry set on the vineyard to evaluate their impact on sunburn.

Based on the bibliographic review conducted, and on the studied problems, different hypotheses were formulated:

A study was therefore conducted at the scale of Château Margaux in order to verify those hypotheses.

For the experimentation to start, different choices had to be made. Among the decisions, the parcel choice and studied modalities were the most important, as they can affect the results of the study. The parameters that affected those decisions will be described in the experimental set-up.

The choice of parcel for this study was made based on different factors. The row orientation, the grape variety, and the frost damage were the main variables that were considered for this choice.

First, to expect some significant results, parcels with a great intensity of sunburn damage from the previous years were chosen, to make sure the results wouldn't be altered by the lack of sunburn.

In 2020, studies were conducted at Château Margaux to evaluate if row orientation had an impact on grape sunburn. As a result, they found that the best orientation to limit grape sunburn was North-East / South -West (Porte, 2020). In order to make sure that the plot chosen for the study would be the worst scenario case, plots with different exposures were chosen, allowing more grape sunburn.

The first parcel chosen is called «Jean Brun Ouest» (JBO) and is oriented East / West. It is part of the «Devant le Château» production block. The second parcel chosen is called «Les 4 Vents Sables» (L4VS) and is oriented North-West / South-East. It is part of the «Plateau» production block. A map with every parcel's orientation is available in Annex 6, and a map with the blocks is available in Annex 4.

Both grapevine parcels produce red grapes from the Cabernet Sauvignon grape variety. Both parcels are planted with a density of 10 000 plants/ha and are older than 10 years old. Those parcels were chosen for their soil homogeneity, to avoid biases.

This specific variety was chosen to study because it represents 52% of the total vineyard and is therefore the most important part of the grape production at Château Margaux. Two parcels were chosen rather than one in case differences in grape sunburn symptoms were observed between orientations.

In order to make sure that the grape production would be homogeneous in the plots chosen, a frost damage counting was performed beforehand. The frosts occurred at the very beginning of April, and the counting was done during this same month, to evaluate if many fruit-bearing bud might be

affected. To do so, a scale from 1 (<30% of buds dead) to 3 (>75% of buds dead) was established. A few rows in the parcels were then chosen where a note to each vine plant was given. Finally, the results were calculated and mapped, so that the company has an idea of which plots were affected by frost.

Both chosen parcels weren't affected by frost, which is an additional reason as for why they were chosen.

For each parcel of land, three modalities were studied. The first is the kaolin sprayed modality (K), the second is the early defoliation modality (ED), and the last one is the control modality (C). To compare modalities, it was decided to combine them all on one same parcel of land, instead of allocating one parcel per study. By doing so, it reduced the uncertainty of the results linked with the homogeneity and type of soil.

To reduce the incertitude linked with the heterogeneity of the plot of land, each modality was repeated 3 times per parcel. By doing so, there were a total of 9 blocks in one parcel, and 18 blocks in total (Figure 6 and Figure 7).

Figure 6: Scheme of the experimental plan of Les 4 Vents Sable, including the repartition of the modalities in the parcel, the
plots chosen, and the captors location

Figure 7: Scheme of the experimental plan of Jean Brun Ouest, including the repartition of the modalities in the parcel, the
plots chosen, and the captors location

Inside each block, a plot of 10 selected plants was followed during the rest of the study. Plots were chosen so that there wasn't any missing plant around and inside the plot, to avoid false results. For example, one missing plant just in front of the studied plot would increase its sun exposure period, and therefore induce error into the results.

The kaolin modality received different sprayings during the season. The spraying solution was prepared with a 20kg/ha dose of kaolin power (Sokalciarbo by AgriSynergie), water, and adjuvant (Vizir by AgriSynergie) at a dose of 20mL/100L of water as advised on the notice. The solution was mixed using a Mixbox mixing tank (Annex 7). The dates of treatment were defined based on the conditions observed. According to the kaolin powder's technical data sheet (Agrisynergie, 2022), the sprayings had to be done between bunch closure and veraison, before any heat wave, and after a leaching above 15mm. The maximum number of sprayings mustn't exceed 4 per year, and the last spraying had to be done at least 15 days before harvest to avoid residues (E-Phy, 2022).

The kaolin sprayings were done on the 14^th of June, the 7th of July, the 22^nd of July, the 29^th of July and the 9^th of August. A calendar is available in Annex 8, and dose calculations were reported in Annex 9.

Figure 8: Photograph of Cabernet Sauvignon leaves before (on le left) and after (on the right) the first kaolin spraying in

For the early grapevine defoliation, a few leaves were suppressed on only one side of the canopy, the North-Eastern side, exposed to sun on mornings. The process was moderate and not drastic, in order to gradually expose the grapes to the sun (Gaviglio 2022). Mostly the side shoots of the plant were suppressed, to allow a better sun exposure, without exposing too much the bunches (Figure 9).

According to bibliography, the defoliation had to be done right after the flowering period, during the fruit setting stage to obtain berries with a higher sun resistance (Serrano, 2018). The defoliation was done in June the 1^st for the Jean Brun Ouest parcel, and June the 2^nd for Les 4 Vents Sable parcel. Early defoliation was performed for both experimental parcels when more than 50% of the parcel was at the fruit setting stage.

For each studied variable, its definition will be reminded, it will be linked with one of the hypotheses/problems, the protocol and the material needed will be presented, and finally the date of data acquisition will be given.

Vintage characterization is done by analyzing the rainfall as well as the different types of temperature for a defined period. The meteorological data will help characterize the 2022 vintage to make sure the conditions were conducive to sunburn.

Meteorological data were provided by Sencrop weather stations located in the «Enclos» and «Plateau» blocks (their location can be found in Annex 4), as well as a global Margaux station. Values of under-shelter temperatures, humidity, rainfall and wind speed were collected for the 2022 growing season.

The following meteorological data: minimum temperature, maximum temperature, average temperature, and rainfall were recorded for each day to characterize the specific conditions of each parcel. Meteorological data collected of each parcel defined the climatic conditions along the growing season.

Based on the collected data, the number of days from March to the end of August with a maximum temperature higher than 30°C was calculated, in order to compare it with the previous years. Sunburn usually happens when temperature is higher than 30°C, so this computation will give information about previous sunburn events. The objective of this measure is to verify the hypothesis that the 2022 weather conditions were conductive to sunburn.

The vegetation zero is the minimum temperature from which a plant can develop. For grapevine, the vegetation zero is 10°C (Ephytia, 2022), meaning that grapevine usually develops faster when temperatures are higher than 10°C. The 10°C base temperature sum is therefore an indicator for grapevine growth over a defined period. Red grape berries are more sensitive to sunburn when mature, due to their darker color, and lower radiation reflectance. The objective of this measure is to verify the hypothesis that the 2022 weather conditions impacted the growth, and therefore the phenological stages precocity of grapevine, resulting in higher sunburn sensitivity.

Since grapevine growing season starts in March, along with the budburst, and ends with harvest, the weather data was only analyzed between March and August 2022.

A plant's phenological stage is characterized by the plant's development during its life cycle. The phenological study of a plant consists of observing the date at which those stages appear (Roussey et al., 2021). The objective of this variable is to define the precocity of both studied parcels, to evaluate their potential impact on the results.

Phenological stages of reference parcels were evaluated using a counting method. The most important stage that needed to be followed for our study is the fruit setting stage when the flowers start to form berries after a successful fertilization.

For the fruit setting stage, the percentage of bunches for one reference plant that were set was counted and calculated. Then, at the parcel's scale, an average was calculated. By repeating this evaluation at different dates, the exact date of the mid-fruit setting stage was defined, to start defoliating the grapevines. The exact same calculation method was done for the other stages.

The results were then compared to previous years, to define the precocity of the 2022 vintage.

Plant vigor is observed by an increase in plant height and density through time (Short and Woolfolk, 1956).

This variable reflects the canopy density and is therefore supposedly negatively correlated with sunburn. This variable was measured to make sure that they weren't any difference between the 3 studied modalities in terms of vigor, that could potentially affect the results.

To evaluate the vigor of the grapevine plants, aerial images were used. The vigor was estimated with an Enhanced Vegetation Index (EVI) based on the exact measurement of reflected light off the plants at different wavelengths, using Vineview (Vineview, 2022). The EVI values range from 0 to 1. Values close to 0 correspond to a bare ground, whereas values close to 1 correspond to a complete vegetation cover (Fraga et al., 2014).

The EVI maps extracted from Vineview dated from May 2022, so that the data was before any kaolin treatment or defoliation.

Vegetation porosity can be defined as the measure of blank spaces in the canopy's vegetation, and is the fraction of the blank portion per the non-blank portion of the canopy (Bélanger, 2017). The higher the porosity, the higher the sun exposure, and the higher sunburn sensitivity (Southey and Jooste, 1991). Vegetation porosity is evaluated by measuring the Leaf Area Index (LAI) for different plants.

The objective of this measure is to control the homogeneity of the followed plots, to make sure that significant differences aren't observed between modalities that could affect the results.

To conduct this measure, the height, length and percentage of blanks in one plant's foliage were evaluated. For each block, this measure was conducted on 1 plant every 3 plants (3 plants out of the 10 reference plants). The measures were done in August the 3^rd, during the grapevine maturation process, when it was evaluated that canopy had stopped its growth.

Grapevine hydric condition can be estimated my measuring the water potential of the vine. There are different types of water potentials. Both potentials are measured using a Scholander pressure chamber (Annex 10). The grapevine water status of the plant is defined by estimating the cell capacity to retain water, using the pressure of a neutral gas applied on the leaf, at different points of the soil-plant-atmosphere system (Ojeda and Saurin, 2014). The more the plant will be stressed, the more pressure will need to be applied to extract sap. The pressure needed represents the current hydric state of the leaf (Dufourcq, 2022; Deloire et al., 2005).

Both measures of water potential will be conducted in order to answer to the hypothesis that spraying kaolin can positively impact the grapevine hydric state in stressing conditions.

Predawn Leaf Water Potential (PLWP) is an estimator to assess soil water availability for species like grapevine at the scale of a parcel (Suter et al., 2019).

This measure gives an estimation of the basic hydric condition of the parcel, to make sure that there are no signs of water stress that could influence results. It is done predawn (from 2am to 6am) and represents a state of balance between the vine plant hydric state and the soil hydric condition. It gives a threshold reference of the current soil water availability for the plants at the scale of the parcel (Deloire et al., 2005).

Only the PLWP for the reference plant of the control modalities of the parcel (3 reference plants) was measured, so that it gives an idea of the evolution of the global hydric condition of the parcel.

For this measure, one leaf of each control modality is cut off the plant, and the petiole is inserted through the lid of the pressure chamber, its cut end remaining exposed. The chamber is then activated, and the petiole is examined until liquid is observed on its surface. When there is liquid, the chamber is turned off and the pressure on the gauge at which water was observed corresponds to the PLWP.

The PLWP measure was taken at different periods during the growing season to obtain an evolution of the water availability through the summer. The PLWP was measured in June the 16^th, July the 11^th and 13^th, and July the 26^th.

The Midday Stem Water Potential (MSWP) is a measure that represents the state of water tension during the plant transpiration, under stressing conditions. This method is usually more precise than the PLWP and is used to compare the hydric constraints of different modalities (Dufourcq, 2022).

The objective of this measure is to compare it between modalities, to define whether or not using kaolin helped reducing the hydric stress of the plant.

This measure is done at the solar noon (around 2pm) after at least 4 days without rain, so it remains precise. The objective of the stem water potential is to give an idea of the grapevine hydric condition during the experimentation period (Dufourcq, 2022).

The chosen leaf is placed in an opaque bag for at least two hours. Then, the leaf is cut off the plant, and the petiole is inserted through the lid of the chamber, its cut end remaining exposed. As for the PLWP, the chamber is then activated, and the petiole is examined until liquid is observed on its surface. When there is liquid, the chamber is turned off and the pressure on the gauge at which water was observed corresponds to the stem water potential.

For this experiment, one reference plant per block for each modality was defined (9 reference plants per parcel). The MSWP of each reference plant was measured, in the Scholander pressure chamber.

Like for the PLWP, the MSWP measure was taken at different periods during the growing season, on June the 13^th, July the 12^th, and August the 11^th.

Leaf surface temperature can be defined as the measure of grapevine's canopy temperature. This measure was proven to be a good indicator of water stress.

Stomatal closure is one of the earliest responses to hydric stress for grapevines. In constant environmental conditions, the leaves' temperatures should decrease because of stomatal conductance increase. The higher the leaves' temperatures, the less the vine plant has access to water (Grant et al., 2016). In normal conditions, grapevine should be able to reduce its leaves temperature with transpiration through stomatal conductance. When the hydric stress becomes important, plant transpiration ceases, and the leaves temperatures rise. Leaves temperature is therefore a good indicator of grapevine water stress (Jackson et al., 1981).

The objective of this measure is to verify the hypothesis that kaolin allows the leaves to reduce their temperatures by reducing the stress of the plant. By comparing the leaf surface temperature between modalities, we can potentially put into light differences of hydric stress.

Additionally, the temperature of sun-exposed leaves was taken during different afternoons in the season, at the bunch level. 30 leaves per modality were randomly chosen (10 leaves per block x 3 blocks) and their temperatures were measured using a manual infrared thermometer (IM8823, iMesure).

For the choice of date to measure the temperatures, the external air temperature should be around 30°C, which is the temperature around which leaves stop their photosynthesis and rise in temperature as they cannot continue to perform evapotranspiration. As kaolin reflects light, studies on grapevine reported that it can reduce the leaves temperature up to 3-8°C (Agrisynergie, 2022), enough for the plant to continue its photosynthesis.

Temperature was measured when kaolin was still present on the leaves, and not after a period of rain where it could have been washed-out. After the first heatwave in June, it rained, washing kaolin off the leaves, not allowing the measure leaf temperature with kaolin. Consequently, this measure was conducted after the other kaolin treatments on July the 11^th to the 13^th, July the 26^th and 28^th, and August the 9^th.

Bunches microclimate was evaluated throughout the season. The main variables evaluated were the bunch temperature and the received luminosity.

The bunch temperature can be defined as the temperature measure of the bunch of grapes at a specific moment of time during the growing season.

Bunch temperature was used in order to verify the hypothesis that applying a kaolin-based particle film on grapes and leaves will reflect a small part of solar radiation, allowing the bunches to get cooler. It was also used to verify the impact of early defoliation on bunch temperature, as no bibliography clearly stated a significant difference.

The microclimate temperature of the fruit zone was measured on the 9 plots of each parcel (3 modalities x 3 repetitions). To measure this temperature, temperature and luminosity captors (HOBO Pendant MX2202, ONSET) were placed on the afternoon sun-exposed side of the row (Figure 10).

The captors were positioned so that they were in the same exposure and temperature conditions as the
studied bunch of grapes. The chosen position of the captors was near bunches of grapes with high

sunburn risk. Those bunches are indeed shady in the morning but exposed on the afternoon. One HOBO captor per block was positioned, representing 9 captors per parcel.

Additionally, 4 under-shelter temperature and relative humidity Tinytag captors were positioned on each parcel. They were placed at different places of the parcel so that they give the mesoclimate of the parcel. Both captor types were programmed so that the data is captured continuously during the season, every 15 minutes. Tinytag captors' results were used to obtain the under-shelter temperature and humidity at a smaller scale than the weather stations to verify if there were differences at the scale of the parcels.

Before activating both the HOBO and Tinytag captors on the parcels, they were calibrated to make sure their data was similar and remove the ones with odd results.

To verify the bunch temperature difference between modalities, the temperature of 30 bunches of grapes per modality was taken with the infrared thermometer (IM-8823, iMesure) at given times. The bunches were chosen randomly and had to be sun-exposed during the afternoon. The measures took place during high-temperature days before and during fruit ripening on the 13^th to 17^th of June, and on the 3^rd of August during maturation, when kaolin was visible on the canopy. Different measures were done in June to calibrate the bunch temperature model at a more precise degree, and later measures were done in August to evaluate the bunch temperature difference after Véraison.

The measure of luminosity can be defined as an estimation of the received luminosity by the bunches of grapes, a factor that can greatly influence the apparition of sunburn symptoms.

The objective of this measure is to give an idea of the received solar radiation for each modality, at the bunch level. This measure should verify the hypothesis that applying a kaolin-based particle film on grapes and leaves will reflect a small part of solar radiation, and that moderate early defoliation will allow sooner and higher sun exposure.

The luminosity data was used to verify those hypotheses, by comparing acquired luminosity between modalities.

Using the HOBO captors, luminosity received by the canopy was measured every 15 minutes of every day of the growing season. This data was used to enrich the bunch temperature calibration model to compare modalities, in order to find for each modality, the correlation degree between luminosity and bunch temperature. The objective of this measure is to give a more precise bunch temperature for each modality, based on the fact that luminosity influences bunch temperature and sunburn symptoms.

Quantifying grape sunburn will help to evaluate the influence of both kaolin and early defoliation on the symptoms. The objective of this measure is to verify if both methods will positively impact sunburn symptoms apparition.

This measure will have the role to verify the hypothesis that the difference in terms of grape sunburn symptoms will be significant between the control modality, the kaolin treated modality, and the defoliation modality.

In order to quantify sunburn symptoms, counts in the vineyard were done throughout the season on both bunches and leaves. For each parcel, 10 grapevine reference plants per block (30 per modality) were observed and their symptoms were evaluated.

Bunch counting is a measure that estimates the number of bunches one grapevine plant will produce. The objective of this measure is to evaluate the average number of bunches per grapevine plant, in order to weight the results, based on the average number of bunches per reference plot.

To do so, for each parcel 5 plots of 10 consecutive plants were defined in different parts of the parcel, and for each plant the number of clusters were counted. By doing so, it gives an idea of the average number of grape bunches per parcel, and therefore an idea of the future yield.

A first count occurred in June the 14^th. Thinning operations took place on both parcels between July the 5th and July the 8^th, leading to another count on July the 13^th.

As mentioned earlier, grape sunburn can lead to two forms of symptoms: the first one being the browning of the berries, and the second one being the withering of the bunch. Bunch sunburn can greatly affect the quality of the berry, as well as the yield, as it can dry up entire bunches.

The objective of this measure is to verify the influence of the modalities on the bunch sunburn symptoms, and to define whether or not the applied methods are working.

To quantify the sunburn symptoms on the bunches of berries, each affected bunch out of the reference plots were counted and the intensity of sunburn symptoms in percentage was visually estimated. The frequency was then calculated by dividing the number of affected bunches by the total number of bunches. Finally, damages caused by sunburn (Frequency*Intensity) were estimated, to give an idea of the losses linked with sunburn.

To obtain the total number of bunches per block, the previously calculated average number of bunches per grapevine plant per parcel (3.4.1) was used. It was then multiplied by 10 (as there were 10 plants per block) to obtain the total number of bunches.

The first bunch sunburn symptoms evaluation counts took place on: June the 22^nd and 27^th. Other visual counts were performed later in July the 20^th and August the 17^th after two main sunburn episodes. In between, another evaluation was performed in July the 8^th and 11^th because thinning was done by hand on the 5^th and 8^th of July for JBO and L4VS respectively.

Although leaf sunburn doesn't have a negative effect on the berry yield and quality, it is a great indicator of heat stress undergone by the plant.

Quantifying leaf sunburn will allow us to verify the effects of both kaolin and early defoliation on the canopy. Under hot and dry conditions, stomata must close to prevent dehydration (Brodribb and Holbrook, 2003). However, as kaolin should reduce canopy temperature by causing stomatal opening, it could potentially cause superior leaf dehydration.

In order to quantify the sunburn symptoms on the leaves out of the 10 reference plants per plot, the number of plants with leaf sunburn were counted and sunburn intensity was visually estimated. By doing so, it gives an intensity and frequency evolution during the followed period of time.

The frequency was calculated by dividing the number of affected plants by the total number of plants per block (10). Just as for the bunch sunburn evaluation, total damages were calculated by multiplying the frequency of leaf sunburn by the average intensity of affected plants. The leaves sunburn symptoms evaluation counts took place on: June the 8^th, July the 26^th, and August the 17^th.

Berry quality evaluation is a process that will help verify the hypothesis that berry quality won't be negatively impacted by kaolin treatments and early canopy defoliation. Quality evaluation will be based on different criteria such as: the berries mass and volume, and the measure of primary and secondary metabolites per modality.

Berries mass represents the weight of the berries while their volume can be defined as the space they occupy.

Because kaolin and early defoliation can significantly reduce sunburn symptoms, they can consequently reduce the number of withered berries, and therefore increase the average berries volume compared to the control modality. However, the volume difference linked with sunburn often isn't significative on grapevine, as berries are small (Brillante et al., 2016).

The objective of this measure is to verify the hypothesis that berry physiology won't be negatively impacted by kaolin treatments and early canopy defoliation.

To evaluate the mass and volume of the berries, the berries that were picked for primary and secondary analysis were used. They were weighted to obtain an approximation of the mass of 100 berries per modality.

The average berry volume was precisely calculated using a Dyostem (by Oenosens). Berries were inserted in the machine for each modality, and their volume was precisely measured.

Grape quality is determined by the contents of the primary and secondary metabolites (Pavlouek and Kumta, 2011).

The objective of evaluating the berries metabolites between modalities is therefore to verify the hypothesis that berry quality won't be negatively impacted by kaolin treatments and early canopy defoliation.

To do so, primary and secondary metabolites have been measured and studied during the maturation phase of the berries, to make sure no significant differences could be observed between modalities.

Primary metabolites come from the primary metabolism that regroups synthesis paths necessary to growth and plant development. Grape primary metabolites involve sugars and organic acids (Chaabani, 2019; Pavlouek and Kumta, 2011).

The objective of comparing primary metabolites levels between modalities is to verify that both treatments won't affect wine quality.

The total acidity of a berry should reduce as it is maturing, while the sugars and pH should increase, as a response to the ripening process. Consequently, the higher the sugar and pH levels, and the lower the acidity levels, the more mature the berry.

To evaluate the primary metabolites per modality throughout the season, tests were run on berries samples. Samples of 200 to 300 berries per modality were collected in plastic freezer bags. Berries were randomly picked on both sides of the canopy, at 4 levels of the bunches.

The samples were then taken to Château Margaux's laboratory where analyses were conducted. The berries were pressed to extract their juice. The pH and density were measured using an automatic titrator. Total and malic acidity were measured using a sequential titrator. Malic acidity measure has a major consequence on the final produced wine acidity. If the measures of malic acidities are significantly different modalities, it will affect the final produced wine.

The sugar concentration in the berries was followed by modality, using the juice density measure.

From July the 21^st to August the 22^nd, analyses were conducted on the berries once a week to follow their evolution until they reach full maturity.

Secondary metabolites come from the secondary metabolism that regroups synthesis paths that aren't necessarily linked with plant growth. Grape secondary metabolites involve phenolic compounds and aromatic substances (Chaabani, 2019; Pavlouek and Kumta, 2011).

As seen earlier in this report (4.2.4), grapevine defoliation is supposed to increase the berry's production of polyphenols and anthocyanins due to a higher sun exposure and protect the berry from sunburn symptoms. To make sure that the berries of the early defoliation modality have a stronger protective skin than the other berries from different modalities, they were analyzed. Measuring the accumulation of polyphenols and anthocyanins in the berries will also give information on potential maturity differences between modalities during the season.

At the same maturity level, the higher the polyphenols and anthocyanins level, the thicker the berry skin.

To evaluate the primary metabolites per modality throughout the season, tests were run on berries samples. Samples of 200 berries per modality were collected in plastic freezer bags. Berries were randomly picked on both sides of the canopy, at 4 levels of the bunches.

The samples were then taken to an external laboratory (Excell) where analyses were conducted. The berries were crushed and centrifuged to analyze their juice using spectrophotometry. For both the anthocyanins and the phenolic compounds, the concentration in the berry was measured, and indexes were calculated. As a result, total anthocyanins, Folin-Ciocalteu index⁶, and total polyphenols / total polyphenols index levels were given.

Analyses were conducted on August the 3^rd and the 10^th, to make sure berries were ripe enough.

When trying to implement new solutions into the current organization, it is important to take into account the managerial and organizational implications linked with these new practices.

The objective of measuring managerial and organizational implications is to answer the following problem: what effects the implementation of these potential solutions will have on the current vineyard management strategy?

To evaluate the managerial implications linked with the implementation of such preventive solutions against grape sunburn, an interview of the vineyard manager of the company was conducted to understand how it will affect the vineyard's activity.

⁶ Measure of optic density based on phenolic compounds oxidation. Reflects the total level of phenolic compounds in berries.

To evaluate the impact of climate change on the production management and on the wine typicity, an interview was conducted with the vineyard manager of Château Margaux.

The interview was completed on July the 19^th, and its content transcribed in Annex 2.

For the characterization of the 2022 vintage, different graphs and tables were produced. To analyze the weather stations data, a graph was modelized representing for each weather station the maximum, minimum, and average temperatures, and rainfall evolution throughout the growing season. To compare the last growing seasons to our results, a table was done to compare the number of days with a maximum temperature higher than 30°C for the last 5 growing seasons. A 10°C base temperature sum was also calculated for the last 5 growing seasons to see when the plant's development was at is highest and lowest, and reported in a graph for comparison. To calculate the 10°C base temperature sum, the average temperatures of each day of the studied period above 10°C were added.

The phenological stages dates results were reported in a table for each parcel, and their results were compared to one another.

To evaluate the plant vigor of out three studied modalities, the EVI values were extracted from the studied plots in Vineview and an average EVI value was calculated for each modality out of their three repetitions. The values were then reported in a table. Then, a one-way ANOVA analysis was conducted using XLSTAT to determine if there are any significant differences between the modalities (XLSTAT, 2022a). If plots were noticed as significantly different from the others in terms of vigor, they were removed from the other results.

For the porosity measure, once the measurements were taken, the Leaf Area Index (LAI) was calculated

The LAI results per modality were reported in a table and a one-way ANOVA analysis was conducted using XLSTAT, to highlight any possible significant differences between modalities (XLSTAT, 2022a). The means resulting from the ANOVA were compared using the LSD function of the Fisher Test on XLSTAT, at a trust level of 0,95.

Both types of water potential measures (PLWP and MSWP) were reported in histogram graphs. Bounds between different hydric intensity values were also implemented into the graph, based on data provided by a study on vine water status (Leeuwen et al., 2009). Differences between MSWP values for each modality were evaluated with a LSD Fisher test at a trust level of 0,95 by conducting an ANOVA, in order to define if values are significantly different between modalities, at different periods of the season.

The leaf temperature data was measured then entered into databases. A one-way ANOVA was then conducted on these measures using a LSD Fisher test at a trust level of 0,95 between the three modalities for each parcel, using XLSTAT, to highlight any significant differences in leaf temperature (XLSTAT, 2022a).

Before implementing HOBO and Tinytag captors into the vineyard, they were calibrated. The calibration consisted in leaving the captors in the same conditions for a few hours, and comparing their results, in

order to make sure that they were homogeneous. The results were modelized in a graph using Excel where we plot the temperature, light and humidity data depending on the time.

The Tinytag captors' data was exported, and the results were plotted using an Excel graph for each parcel. Captors were compared to one another to verify potential intra-parcel temperature differences. The comparison dates chosen (between June the 17^th and the 19^th) correspond to the first heatwave event in June, to make sure that captors data do not differ with high temperatures.

The IR manually taken temperatures between modalities were not only used for the bunch temperature model, but also for punctual comparison between modalities, during hot sunny days. The results were reported in a graph where measured bunch temperatures were compared between modalities for each studied parcel. A one-way ANOVA was also conducted on those results, using XLSTAT, to verify if the bunch temperature was significantly different between modalities (XLSTAT, 2022a).

To acquire the bunch temperature for the studied period of time, the IR manually taken temperatures needed to be compared to the HOBO light and temperature data at given days and hours to produce a database. In the database, data was analyzed by modality and parcel at different stages of the growing season.

Based on the HOBO and IR temperature and light data, multiple linear regression analysis for each modality (6 in total: 3 modalities * 2 parcels) were done using XLSTAT to give the degree of influence of each variable on the bunch temperature (XLSTAT, 2022b). By doing so, XLSTAT gave us correlations between data in order to produce an equation for the bunch temperature. Before using the formula produced, the p-values were checked to make sure they were significant. Once the IR bunch temperature equations were obtained, they were used to produce a bunch temperature calibration model to apply to the HOBO data. The modelized bunch temperatures between modalities were then compared to define if there were significant differences justifying the use of kaolin or canopy defoliation. Those bunch temperatures were compared using a graph in Excel, and the control modality was used as a reference.

The bunch luminosity data was used for the bunch temperature calibration model where it was implemented into the multiple linear regression analysis as a variable.

Bunch counting data was used to be implemented into the calculation of sunburn symptoms frequency and damages on both bunches and leaves. The frequency was calculated by dividing the number of bunches with sunburn in the reference plot by the total number of bunches in the reference plot (calculated by multiplying the average number of bunches per plant by the number of plants by reference plot). The number of bunches was also reported in a table.

The quantification of bunch and leaf sunburn symptoms were processed the same way. Graphs were produced in order to compare the evolution of sunburn frequency, intensity and damages between modalities throughout the season. One-way ANOVAs were also done using XLSTAT and LSD Fisher tests at a trust level of 0,95 were done to verify the damage significance between modalities, to be able to conclude if both methods were actually efficient (XLSTAT, 2022a). The results were reported in tables.

Primary and secondary metabolites, as well as mass and volume data were used to produce graphs using pivot tables in Excel, where the evolution of all measures were plotted throughout maturation. To evaluate the sugar concentration in the berries, a table was used to convert the measured juice density value in sugar level (g/L) (Schaeffer 2018).

The interview conducted for the managerial and organizational implication part was used to report information about the consequences of implementing new solutions in the vineyard practices.

For each LSD Fisher test conducted using an ANOVA in XLSTAT, two groups with no letter in common are considered as statistically different (p-value < 0,001). The values reported in tables in the results regroup the average, the error margin, and the group letter.

After the study was set up, it started along with essential measures for each parameter. The objective of this part is to remind the studied data for every parameter, present the measured indicators, compare the data to references, and finally interpret the data to answer our problems and validate our hypotheses.

Vintage characterization is an essential factor that will help define the conditions of the study and their influence on its results. The 2022 vintage will be characterized based on its weather conditions as well as on the dates of its phenological stages.

To characterize the 2022 vintage weather conditions, two graphs were produced with data from the two weather stations near the studied parcels. Because the data from both weather databases are very similar due to the geographical proximity of both parcels, only the data from the Enclos weather station will be presented on Figure 11, while the data from the Plateau station will be available in Annex 11.

Figure 11: Evolution of the maximum, minimum and average temperatures as well as the rainfall for the 2022 growing
season, from March the 1^st until August the 22^nd, based on the Enclos weather station data.

Based on Figure 11, the 2022 wine growing season in Margaux can be characterized by important rainfall episodes between March and April with low temperatures. The season also faced a frost episode in April between the 3^rd and the 5^th. Those episodes didn't prosper during the season, and temperatures rose until they reached heat waves mid-June, mid-July, and mid-August. Overall, the 2022 growing season can be characterized as rainy until May, then hot and dry from June to September. The maximum reached temperature was 41,4°C on July the 18^th.

From 30°C (red line on Figure 11), the sunburn risk increases (3.1). According to the Margaux weather station database, there were 34 days during the 2022 wine growing season where the temperatures were higher than 30°C and the sunburn risk was growing. Consequently, the 2022 growing season can be characterized as favorable to sunburn development, making this study more significant.

In order to compare the risk of sunburn linked with temperature peaks, the last 5 growing seasons were compared, and the number of days that reached a maximum temperature higher than 30°C were reported in Table 2, according to the Margaux local Sencrop weather station.

Table 2: Comparison of the number of days where the maximum temperature (Tmax) was higher than 30°C, for the last 5
growing season, from March the 1^st to August the 22^th, according to the Margaux Sencrop weather station data

More days above 30°C were observed in 2022 than in the last 5 years. In 2021, the number of days with a maximum temperature above 30°C were lower than the other years, resulting in less sunburn. This could lead to think that the 2022 growing season was more affected by grape sunburn.

To compare and evaluate grapevine's plant growth over the 2022 growing season, the 10°C base temperature sum was calculated for the last 5 growing seasons in Figure 12.

Figure 12: Comparison of the 10°C base temperature sum for the last 5 growing seasons, from March the 1st to August the
22th, based on the Margaux Sencrop weather station data

Based on Figure 12, the 10°C base temperature sum seems to be higher during the 2022 growing season compared to the other seasons. It is higher than the average temperature sum between 1996 and 2015. The 2021 and 2019 seasons seem to be lower in terms of temperature sum than the other years.

Thus, the phenological stages of the 2022 growing season could have been shifted resulting in a higher berry sunburn sensitivity.

Overall, the 2022 growing season in Margaux can be characterized by important heatwaves causing intense plant growth. This season was hotter than the last 5 seasons, and the 10°C base temperature was higher than the other seasons. All the results show that the 2022 vintage meteorological data were conducive to grape sunburn.

The dates of the key phenological stages for the two studied parcels were reported in Table 3. The dates of those stages for the last 4 growing seasons for both parcels were reported in Annex 12.

Based on the Annex 12, the mid-bud burst dates were tardive as temperatures remained low during April and March, but the mid-flowering date was early due to high temperatures in May. A frost-freeze event occurred in April, but no late frost event was observed. The mid-ripening dates were also early, due to the high 10°C temperature sum, compared to the other years. As the mid-ripening stage was shifted, the berries started to change color earlier, and were therefore more sensitive to solar radiation, affecting their sunburn sensitivity.

Globally, both parcels' phenological stages were close to one another. The parcels can therefore be compared without their phenological stages affecting the results.

The EVI maps from Vineview (Annex 13 and Annex 14) show that the Jean Brun Ouest parcel is more vigorous than Les 4 Vents Sable. They also show that there are zones inside the parcels where the vigor isn't homogeneous with the rest. For example, in Jean Brun Ouest, the East part of the parcel is vigorous whereas the West part isn't.

The left of Les 4 Vents Sable parcel is an important non-vigorous zone. To make sure that our observations remain homogeneous, plots with higher EVI values were chosen, apart from this zone, so that it doesn't affect the study. To verify that the EVI differences between modalities were minor, a Fisher Test at a trust level of 0.95 was conducted using the LSD function. The results of this test were reported in Table 4 and Table 5.

Table 4: Results of the LSD Fisher Test on Enhanced Vegetation Indexes (EVI) of the different modalities in the JBO parcel

Table 5: Results of the LSD Fisher Test on Enhanced Vegetation Indexes (EVI) of the different modalities in the L4VS parcel

Based on the averaged EVI data per modality and on the Fisher Test results, the differences of EVI between modalities aren't significant (all modalities were classified in the same group).

Consequently, there are no significant differences in plant vigor between modalities that could potentially affect the results. Plant vigor is therefore homogeneous in the studied plots and won't impact the results of sunburn symptoms.

To make sure that the different modalities were studied in similar conditions, the canopy porosity values calculated from the photographs taken were reported in Table 6 and Table 7.

Table 6: Results of the LSD Fisher Test on Leaf Area Indexes (LAI) of the different modalities in the JBO parcel

Table 7: Results of the LSD Fisher Test on Leaf Area Indexes (LAI) of the different modalities in the L4VS parcel

Based on the results from the Fisher test, there aren't any significant differences between the average vegetation porosities on both parcels (all modalities were classified in the same group).

Consequently, it can be concluded that all the modalities inside both parcels are on average equally exposed to sun. Porosity won't affect the results on sunburn symptoms between modalities.

To determine the hydric state of the grapevine plants, two types of indicators were used to evaluate the potential impact of kaolin spraying and vine defoliation: water potentials, and leaf temperature.

To start with, the Predawn Leaf Water Potential measure was evaluated throughout the season, and the values were reported in Figure 13.

Because of the weather conditions of the 2022 vintage, the hydric constraint grew at the scale of the parcel from June to August. The JBO parcel has on average a higher water deficit than the L4VS parcel.

Both parcels were in stressing conditions by the end of the growing season. Consequently, it can be concluded that there were signs of water stress during the season, that could potentially influence the results.

Then, the Stem Water Potential was evaluated throughout the season as well, and the values were reported in Figure 14.

For every modality on both parcels, the water constraint was initially low and became moderate to high later in the season.

By comparing this variable between modalities, it shows that for both parcels the water constraint is on average lower for the kaolin modality, in stressing conditions. To verify this hypothesis, an LSD Fisher test was conducted, and its results were reported in Table 8 and Table 9.

Table 8: Results of the LSD Fisher Test on August the 11th Stem Water Potentials (SWP) of the different modalities in the

Table 9: Results of the LSD Fisher Test on August the 11^th Stem Water Potentials (SWP) of the different modalities in the

Based on the Fisher test results, the kaolin modality is significantly less stressed than the early defoliation modality for the L4VS parcel. However, based on the PLWP results, the JBO parcel was more stressed than the L4VS parcel, making it harder for kaolin to improve water use.

Consequently, it can be concluded that both water potential measures validated the hypothesis that spraying kaolin can slightly improve the grapevine hydric state up to a certain degree of stressing conditions.

The leaf temperature data was taken with an IR thermometer for each modality and the results were reported in Figure 15.

Figure 15: Leaf temperature per modality for both parcels, taken with an infrared thermometer, between July the 11th and

Figure 15 shows slight differences in leaf temperature between modalities. It can be observed that the kaolin modality is on average cooler by 2 to 3°C than the other modalities. However, based on the uncertainty bars on Figure 15, the temperature differences do not seem to be significant.

In order to verify this hypothesis, an ANOVA was conducted using an LSD Fisher test, and its results were reported in Table 10 and Table 11.

Table 10: Results of the LSD Fisher test on leaf temperature of the different modalities in the JBO parcel

Table 11: Results of the LSD Fisher test on leaf temperature of the different modalities in the L4VS parcel

Based on the ANOVA results, leaf temperature measurements showed a significative difference between modalities based on their group classification. Overall, it can be observed that the kaolin modality is significantly lower in leaf temperatures than the two other modalities for most measurements. Significative differences in terms of leaf temperature between the early defoliation and the control modalities were rarer, and both modalities were considered close.

Consequently, this does prove that kaolin reduces significantly leaf temperature, and validates the hypothesis that kaolin allows the leaves to slightly reduce their temperatures by reducing the stress of the plant, even by just a few degrees.

As seen earlier in this report (4.2.3), kaolin-spraying can influence bunches temperature, due to a higher reflection of the radiation. To verify if kaolin significantly reduces the bunch temperature, bunch temperature was measured during the growing season to conduct statistical comparisons between modalities. Moreover, those measures helped calibrate a bunch temperature model for the growing season.

In order to diminish the risks of error, the captors chosen to be placed in the plots were calibrated to make sure they wouldn't produce wrong values. The IR thermometer, the HOBO captors, and the Tinytag captors were all calibrated to reduce risks of errors.

To reduce the risks of error of berry and leaf temperature between modalities, all the measures were conducted with the same thermometer. For one given parcel, only one person was in charge to take all the measurements, to avoid the uncertainty linked to the observer.

Before implementing HOBO captors in the reference plots to acquire data, they were calibrated. Two additional captors were ordered in case some weren't working. The results of the temperature and light data were reported in Figure 16 and Figure 17.

Figure 16: Comparison of temperature data between 20 potential usable HOBO captors, on the 2^nd and 3^rd of June

Figure 17: Comparison of light data between 20 potential usable HOBO captors, on the 2nd and 3rd of June

Based on those graphs, results are overlaid, and the maximum difference in temperature between captors was 0.002°C, and 0.01 for the luminosity data. No captor showed values significantly different than the others, so the captors needed for the reference plots were randomly chosen.

Consequently, all differences between values under 0.002°C and 0.01 luminosity will not be considered as significant for interpretation.

Before starting the study, there were 10 TinyTags but the study only needed 8. This calibration helped to determine which ones were going to be used and which ones weren't.

The temperature and humidity data were plotted on Figure 18 and Figure 19 using an Excel pivot chart.

Figure 18: Comparison of temperature data between 10 potential usable TinyTag captors, on the 23^rd and 24^th of May

Figure 19: Comparison of relative humidity data between 10 potential usable TinyTag captors, on the 23^rd and 24^th of May

Based on the results, the values of the TinyTag number 7 were too different from the rest of the captors. Captor number 7 was therefore not included in the study.

When comparing all the other values, excluding captor number 7, a maximum difference of 0,458°C and 4,553%RH was observed between captors. Captor number 10 was also excluded, whose temperature values were slightly under the rest of the lot.

Therefore, all differences between values under 0,458°C and 4,553%RH will not be considered as significant for interpretation.

The parcels under-shelter temperature and humidity were measured using Tinytag captors at different positions. As both parcels results were similar, only the results from JBO were reported in Figure 20, and the rest of the results are available in Annex 15.

Figure 20: Tinytag captors temperature and humidity results on the JBO parcel between July the 17th and the 19th

Based on Figure 20, no significant differences were observed between captors in terms of temperature and humidity at the scale of the parcels.

Consequently, this verifies the hypothesis that the under-shelter temperature and humidity values are homogeneous and couldn't have affected the measured temperature differences between modalities.

The bunch temperature was punctually manually measured for each modality at different moments of the growing season. The infrared measured temperatures were compared at one precise moment for the three modalities during warm and sun-exposed days, and the results were reported in Figure 21.

Figure 21: Comparison of average bunch temperature per modality at different times of the day, on the sun-exposed side of
the canopy, taken by an infrared manual thermometer, between June the 13^th and August the 3rd

At the beginning of the measures, a slight difference in temperatures was observed between modalities. During the berries ripening, the same tendency was observed, but the differences stayed minimal.

The defoliation of the grapevine reduces its porosity. Consequently, the early defoliation modality should have higher bunch temperatures than the other modalities, because of the higher sun exposure. Based on the graph, the bunch temperatures differences do not seem significantly different between modalities.

In order to verify this hypothesis, the significance of the values was evaluated by conducting an ANOVA using the LSD Fisher test method. The results of the Fisher test can be found in Table 12 and Table 13.

Table 12: Results of the LSD Fisher test on bunch temperature of the different modalities in the JBO parcel

Date	Kaolin		Early Defoliation		Control
June the 13th	27.75	#177; 0.31 A	26.83	#177; 0.31 B	27.71	#177; 0.31 A
June the 15th	36.70	#177; 0.34 A	36.07	#177; 0.34 A	36.70	#177; 0.34 A
June the 16th	22.12	#177; 0.24 A	22.01	#177; 0.24 A	22.43	#177; 0.24 A
June the 17th	30.06	#177; 0.35 A	30.30	#177; 0.35 A	30.64	#177; 0.35 A
August the 8th	39.36	#177; 0.34 B	41.35	#177; 0.34 A	40.68	#177; 0.34 A

Table 13: Results of the LSD Fisher test on bunch temperature of the different modalities in the L4VS parcel

The results show that the punctual bunch temperature measures weren't always significantly different between modalities as they were often classified in the same group. There aren't enough measures where the kaolin modality was significantly lower in bunch temperature than the other modalities to conclude that kaolin reduces significantly bunch temperature. When the measures are significantly different, the differences are very low (1 to 2°C).

Consequently, it doesn't verify the hypothesis that applying a kaolin-based particle film on grapes will reduce bunch temperature, due to the lack of measures. The result might have been significant if measures were done continuously for one day. To verify this hypothesis, the bunch temperature model measured temperatures all day long.

To obtain the precise bunch temperature model for each modality, the model was first calibrated, then applied to data during heatwave events in the season.

To produce a bunch temperature simulation, the bunch temperatures weren't measured during nighttime, and only the daytime temperatures differences will be taken into account. The model is based on the pre-véraison bunch temperatures.

To model the average bunch temperature for each modality at different moments of the day, the followed equation was synthetized by XLSTAT:

CTemp_HOBO: Coefficient Temp_HOBO given in the model's parameters CLight_HOBO: Coefficient Light_HOBO given in the model's parameters Temp_HOBO: Temperature of the bunch microclimate recorded by the HOBO captor Light_HOBO: Light of the bunch microclimate recorded by the HOBO captor

For every of the 6 produced models, the HOBO temperature and light variables of the bunch microclimate were considered in the model as being significative.

Figure 22 represents the result of the bunch temperature model for the control modality of the L4VS parcel. The other results of the significant linear regressions can be found in Annex 16 to Annex 20.

Figure 22: Multiple linear regression model from XLSTAT between the IR thermometer bunch temperature and the HOBO
captor recorded light and temperature data for the control modality in the Les 4 Vents Sable parcel

Figure 23: Evolution of bunch temperature on the JBO parcel between the 17th and the 19th of June 2022

Figure 24: Evolution of bunch temperature on the JBO parcel between the 12th and the 15th of July 2022

The bunch temperature models for each modality were applied to different periods during the 2022 summer where temperatures were high, and sunburn happened. The results for three heatwaves were graphically represented on Figure 23, Figure 24 and Figure 25. The results on both parcels were similar, so only the JBO parcel results will be analyzed in this part, and the L4VS results can be found in Annex 21.

Figure 25: Evolution of bunch temperature on the JBO parcel between the 10th and the 12th of August 2022

For the JBO parcel, the followed bunches of grapes were exposed on the South part of the canopy and reached a temperature peak between 2 and 4 PM. During the first heat wave (Figure 23), the bunches reached a maximum of 38,8°C for the kaolin modality, 43°C for the early defoliation modality, and 40°C for the control modality.

During the second heatwave (Figure 24), the bunches reached a maximum of 39,2°C for the kaolin modality, 45,8°C for the early defoliation modality, and 43,9°C for the control modality.

Lastly, during the August heatwave (Figure 24), the bunches reached a maximum of 40,08°C for the kaolin modality, 46,47°C for the early defoliation modality, and 42,89°C for the control modality.

Nevertheless, when comparing where the temperatures reached a plateau, it can be observed that the early defoliation modality and the control modality values are very similar, and only the kaolin modality is significantly cooler.

Overall, the differences between modalities were similar before and during véraison. The bunch temperature difference between the highest temperature of the control and the kaolin modalities is 1,2°C for the June heatwave, 4,7°C for the July heatwave, and 2,81°C for the August heatwave.

Those results verify the hypothesis that applying a kaolin-based particle film on grapes and leaves will reflect a small part of solar radiation, allowing the grapes to get cooler.

Sunburn symptoms were evaluated on both bunches of grapes and leaves. The measure of bunch sunburn symptoms will verify the influence of the modalities on berry sunburn, and therefore will help to define whether those methods can save grape yield and quality or not. Additionally, the leaf sunburn measure is an indicator of the sunburn pressure as well as the hydric state of the plant.

Due to grape thinning operations in July, two counts occurred. The results were reported in Table 14.

Table 14: Evolution of the bunch number per parcel before and after thinning operations

Based on the results, the final number of bunches per plant was reduced to obtain similar values. Consequently, the number of bunches per plant isn't significantly different between modalities.

The first evaluation of bunch sunburn symptoms took place in June, after a high-temperature week where the ambient temperature went up until 42°C. Other visual counts were performed after each high-temperature episode. The frequency as well as the intensity of bunch sunburn were represented for both parcels for each modality in Figure 26.

Figure 26: Evolution of bunch sunburn frequency and intensity on JBO and L4VS, from June the 22nd to August the 17^th

On Figure 26, the bunch sunburn symptoms seem to have decreased mid-July. This is due to thinning operations that took place on July the 5^th on JBO and the 8^th on L4VS. A lot of bunches affected with sunburn were removed, explaining the differences between the first and the second measure.

The frequency as well as the intensity of bunch sunburn rose for all the modalities of JBO and L4VS from the 8^th and 11^th of July until the 17^th of August. The control, early defoliation and kaolin modalities frequencies respectively rose by 12%, 1,9%, and 1,9% for JBO and 9,2%, 4,3%, and 3,1% for L4VS during this period.

From these measures, it could be concluded that overall, the kaolin and the early defoliation modalities had a noticeable effect on reducing bunch sunburn frequency.

In order to evaluate the losses linked with sunburn for each modality, the bunch damages (frequency*intensity) were calculated and represented on Figure 27.

Figure 27: Evolution of damages linked with sunburn on bunches per modality, from June the 22^nd to August the 17^th

According to Figure 27, yield loss (damage) estimation due to grape sunburn seemed to be significantly reduced by kaolin spraying and by early plant defoliation by the end of the season. By August the 17^th, losses due to sunburn were estimated to 0,69% on JBO and 2,25% on L4VS for the control modality, 0,52% on JBO and 0,51% on L4VS for the kaolin-sprayed modality, and 0,31% on JBO and 0,51% on L4VS for the defoliated modality.

As seen on Figure 27, the results are more significant on the L4VS parcel due to higher intensity and frequency. Only the L4VS parcel will therefore be analyzed.

On L4VS on the 27^th of June, early defoliation seemed to have reduced sunburn symptoms by 85%, while kaolin reduced symptoms by 67%. If the 11^th of July results are taken as a base zero due to thinning operations, new damages on the 20^th of July are evaluated to: 0,22%, 0,12% and 1,02% for respectively early defoliation, kaolin and control modalities. On the 20^th of July, early defoliation therefore reduced damages by 78%, while kaolin reduced them by 88%.

With the 11^th of July results as a base zero, damages on the 17^th of August are evaluated to: 0,3%, 0,22% and 2,14% for respectively early defoliation, kaolin and control modalities. On the 17^th of August, early defoliation reduced damages by 86%, while kaolin reduced them by 90%.

An ANOVA was conducted between modalities, to make sure that the damage differences were significant. The results were reported in Table 15 and Table 16.

Table 15: Results of the LSD Fisher test on berry sunburn damages of the different modalities in the JBO parcel

Table 16: Results of the LSD Fisher test on berry sunburn damages of the different modalities in the L4VS parcel

While a significant difference can be observed between the control modality and the others (they were classified in different groups), both the Kaolin and early defoliation modalities weren't classified as significantly different.

Consequently, this verifies the hypothesis that kaolin as well as early defoliation both have a positive impact on grape sunburn.

After each heatwave of the growing season, evaluations of leaf sunburn damages was performed additionally to the bunch sunburn evaluation. The evaluations took place between July the 8^th and August the 17^th. The frequency as well as the intensity of leaf sunburn were represented for both parcels for each modality in Figure 28.

Figure 28: Evolution of leaf sunburn frequency and intensity on JBO and L4VS, from June the 22nd to August the Xth

On Figure 28, the leaf sunburn symptoms seem to have globally increased between July and August. The frequency as well as the intensity of leaf sunburn rose up for all the modalities of JBO and L4VS from the 8^th and 11^th of July until the 17^th of August.

Overall, all the modalities seemed to all have been subject to intense leaf sunburn due to the high-temperatures and low rainfall episodes.

Figure 29: Evolution of damages linked with sunburn on leaves per modality, from June the 22^nd to August the 17^th

According to Figure 29, leaf damage estimation due to grape sunburn doesn't seem to be significantly different between modalities, even if small differences can be observed between modalities. By the end of the season, leaf sunburn damages were estimated to 26% on JBO and 16% on L4VS for the control modality, 22% on JBO and 10,5% on L4VS for the kaolin-sprayed modality, and 19% on JBO and 16% on L4VS for the defoliated modality.

An ANOVA was conducted between modalities, to verify if the damage differences on leaves were significant. The results were reported in Table 17 and Table 18.

Table 17: Results of the LSD Fisher test on leaf sunburn damages of the different modalities in the JBO parcel

Table 18: Results of the LSD Fisher test on leaf sunburn damages of the different modalities in the L4VS parcel

According to the ANOVA, no significant difference (they were all classified in the same group) can be observed between the three modalities. Therefore, leaf sunburn symptoms were overall the same for each modality.

Consequently, kaolin and early defoliation do not have a significant impact on leaf sunburn symptoms. And while kaolin reduces leaf temperature and berry sunburn, it does not significantly cause higher leaf dehydration.

As a result to both measures, even if all the modalities faced different bunch sunburn damages, their leaf sunburn symptoms were similar. This can be interpretated the fact that in the same stressful environment where sunburn should thrive, the kaolin and early defoliation modalities are efficient to protect the berries.

For each modality, the mass and volume of 100 berries were measured from Véraison, to evaluate any potential difference. The results from both parcels being similar, only L4VS results were reported in Figure 30. The JBO results are available in Annex 22.

Figure 30: Evolution of mass and volume of 100 berries between July the 21st and August the 22nd, for the L4VS parcel

Based on Figure 30, the berries' size and volume seem to be different between modalities by the end of the season. The peak of volume hasn't been reached yet, as berry maturity usually stops later in September.

Indeed, the kaolin modality seems to present bigger berry sizes and volumes. Theoretically, the use of kaolin should lower the berries temperature during hot days, reducing the berries transpiration resulting in a berry volume rise of 7%, as it has been studied on Sauvignon Blanc and Merlot (Coniberti et al., 2013; Shellie and Glenn, 2008).

Consequently, the mass and volume measures verify the hypothesis that berry physiology wasn't negatively impacted by kaolin treatments and early canopy defoliation. On the contrary, kaolin treatments significantly increased the berries' size and volume.

Primary and secondary metabolites were measured during the berry maturation on both studied parcels for each modality. The results of those measures and analyses were reported in graphs. The analysis results from the external laboratory (Excell) are available in Annex 23Annex 23.

As both parcels had similar results in terms primary metabolites, only L4VS results were analyzed in this part, and results from the JBO parcel were reported in Annex 24.

Figure 31: Analysis results of berry maturity per modality, between July the 21st and August the 22^nd, for the L4VS parcel

As it can be observed on Figure 31, by the 22^nd of August, the modalities levels of pH, sugar, malic acid, and total acidity are similar.

On the 29^th of July, it can be observed that the early defoliation modality seemed more advanced by the others, due to its higher values in pH, and lower acidity. However, no significant difference can be observed by the end of the maturation process.

Consequently, this verifies the hypothesis that kaolin sprayings and early defoliation do not impact berry maturity, and therefore wine quality.

The total phenolic compounds were evaluated using the Folin Index. The polyphenols and anthocyanins levels were measured and the TPI was calculated. The results were reported in Figure 32.

Figure 32: External laboratory analysis results of anthocyanins and phenolic compounds per modality, between August the

According to the results, neither the total phenolic compounds nor the total anthocyanin concentration significantly differ between kaolin and control modalities, meaning that kaolin spraying did not have a significant effect on both compounds. However, early defoliation levels seem slightly higher than other modalities for both metabolites, but the difference isn't significant.

Globally, it can be concluded that the measured physico-chemical characteristics on the different modalities weren't significantly influenced by neither the kaolin spraying, nor the early defoliation of the canopy. Consequently, both potential solutions against grape sunburn won't affect the quality of the harvested berries, and therefore the quality of the produced wines.

However, it has been observed that early defoliation increases polyphenol and anthocyanins production in berry skin, validating the hypothesis that exposing plants to solar radiation sooner helps forming a stronger protective skin that will be able to resist sunburn, without affecting grape quality.

Assumed from the results of this study, grape sunburn adaptation comes with important management changes and implications. Including sunburn preventive solutions into the vineyard work calendar represent additional workload that needs to be managed. For example, implementing kaolin sprayings and early defoliation imply to free some time, and reduce time allocated with other types of tasks.

Thanks to the interview conducted with the vineyard manager (Annex 2), early defoliation could be included in the existing work calendar, if it is done early and at the good phenological stage, to make sure that the bunches have enough time to adapt to sun exposure. Kaolin sprayings could also be managed if it is proven that it doesn't affect the organoleptic parameters of the wines. However, both solutions will necessitate additional work as they cannot be merged with other existing tasks. For example, kaolin powder cannot be implemented inside their regular vineyard treatments they already conduct, as it might affect the application process.

In terms of expertise, processes, and workforce, the limits that Château Margaux will face to implement those solutions are: workforce availability, machinery availability, weather conditions, and workload conducted at the same time.

In terms of managerial adaptation, this means that the company will be most likely to hire supplementary working force to complete this job.

Overall, both solutions will induce management changes, will come with challenges, and will be time and cost-bearing.

The study took place during the 2022 growing season. The conditions, results, as well as the limits of the study were reminded in order to conclude on the efficiency of the studied potential solutions against grape sunburn.

Regarding the conditions of the study, weather conditions as well as the parcels homogeneity were two main factors that have impacted the results, and that differ between vintages.

Weather conditions can greatly influence this study. For example, this study was already conducted in 2021 with three modalities: control, kaolin spraying on bunches and leaves, and kaolin spraying on bunches only. However, the 2021 weather conditions weren't keen to sunburn development, as it rained a lot, and there wasn't any heatwave.

Consequently, it was harder to decipher a significant difference between modalities, as they weren't much affected by sunburn, and it was harder to define a good date to apply kaolin on the canopy. It is however important to conduct this study on different types of weather conditions, so that it can be adapted and improved.

The results found in this study on weather conditions confirm the bibliography results linking higher sunburn intensity with higher light and temperature conditions (Schrader et al., 2009; Gambetta et al., 2021; Araújo et al., 2018). It also confirms the link between temperatures higher than 30°C and sunburn (Pastore et al., 2013), based on the results from the last 5 growing seasons.

Rain can also greatly affect this study on the kaolin modality, as the kaolin clay can be washed away by rain.

High temperatures such as the ones faced during the 2022 growing season were perfect for this study, as they surely caused sunburn on both parcels. However, the season was dry, and caused water deficit, intensifying the sunburn symptoms, even on the kaolin and early defoliation modalities, as it was found in bibliography (Cook et al., 1964; Gambetta et al., 2021). Additionally, a climate like the 2022 vintage reflects the potential climatic conditions the Médoc vineyard will face in the future due to climate change.

For the 2022 study, as the rain episodes were rare between June and August, the kaolin sprayings lasted for long periods of days. Visually, both the leaves and bunches were covered by kaolin on both sides of the canopy, and the defoliation allowed the bunches to be significantly more sun exposed than the control modality.

The results of porosity and EVI clearly show that the modalities were homogeneous in terms of plant physiology, reducing uncertainties limiting biases.

The EVI values between modalities weren't significantly different, which reflects a global homogeneity in terms of plant vigor for both studied parcels.

However, those results do not consider the zones of the parcels where the vigor was low, and only considered the studied plants. It can therefore be imagined that significantly different EVI values could have been observed if the studied plots were chosen differently.

No link between vigor and sunburn were found, as opposed to what was found in other studies (Smart, 1985), due to the homogeneity of the studied plots.

Regarding the vegetation porosity values, the Leaf Area Indexes (LAI) between modalities weren't significantly different either. The studied plots were consequently equally exposed to sun, limiting biases linked with sun exposure, as it was found in bibliography results (Southey and Jooste, 1991).

It can be said that homogeneity between modalities was hence controlled based on the porosity and EVI values, limiting biases linked with plant growth.

Overall, the results of the study were conclusive and showed that both kaolin sprayings and early defoliations had an impact on grape sunburn. Both solutions being however different, they affected grapevine physiology as well as berries quality differently.

In this part, the effects of both studied solutions against grape sunburn on grapevine physiology will be discussed. More precisely, their consequences on the plants' hydric state and sunburn symptoms will be resumed.

Based on the measures of both water potentials and leaves temperature, the kaolin sprayings have significantly improved grapevine hydric state, by reducing its temperature. The results found confirm the bibliography results, showing that kaolin can diminish hydric stress (Glenn and Puterka, 2010; Glenn et al., 2010). Kaolin sprayings can therefore be considered as a good solution against grapevine hydric stress. However, early defoliation only seemed to have increased water stress, by increasing canopy porosity due to removed leaves.

In this study, kaolin reduced leaf temperature between 2 and 3°C on average, which is low, as the bibliography results predicted a 3 to 8°C reduction (Agrisynergie, 2022).

Consequently, it can be concluded that kaolin was the best modality out of the two studied solutions to reduce water stress and improve grapevine physiology.

The bunch temperature results showed significantly differences between modalities, contrarily to leaf temperature. However, when the bunch temperature model was applied to high temperatures episodes, differences in temperature peaks were observed between modalities. The kaolin modality was the coolest, while the early defoliation modality was the hottest.

As grape sunburn is mostly a result of high solar radiation and temperatures, it could have been expected that the early defoliation modality had more sunburn symptoms. However, based on the sunburn evaluation results, the control modality was significantly more affected than the two other modalities. The results helped validate the hypothesis that both kaolin and early defoliation can reduce grape sunburn symptoms on bunches by acting differently on grapevine physiology.

According to studies, kaolin sprayings should increase light reflectance and reduce the plant's sensitivity to sunburn (Yazici and Kaynak, 2009; Lobos et al., 2015). On the other hand, early defoliation should increase sunlight exposure, resulting in higher skin thickness and lower sunburn sensitivity (Pastore et al., 2013; Solovchenko, 2010).

The results found in this study confirm both hypotheses, as damages linked with sunburn were significantly reduced by both kaolin sprayings and early defoliation.

In order to verify the potential impact of the modalities on berry quality, some analyses were conducted, and results were analyzed.

Based on the results, kaolin sprayings had a positive effect on grapevine physiology. Indeed, kaolin increased berry size and volume compared to other modalities.

The early defoliation modality, due to a higher and sooner berry sun exposure, presented a slightly higher anthocyanin and polyphenols concentration than the other modalities. However, the difference between modalities being unsignificant, other factors might have helped reduce sunburn sensitivity for this

modality. For example, the aeration of the canopy linked with defoliation could have potentially helped reduce bunch temperature and therefore sunburn.

When looking at other primary and secondary metabolites, no significant difference can be observed between the three modalities. It can therefore be imagined that based on those results, neither kaolin nor early defoliation have negatively impacted berry quality. However, no conclusion can be taken on the final wine quality, as other parameters are to be taken into account, such as unmeasurable compounds and berry taste, that can only be evaluated by conducting tastings.

As a conclusion on the study results, it can be said that both methods worked differently on grapevine physiology but were both efficient on grape sunburn. While kaolin proved to improve the plant's hydric condition and reduce bunch temperature, early defoliation built up the berries' tolerance to sun exposure.

Both studied solutions at the scale of the vineyard can present some technical challenges linked with their application.

Kaolin sprayings are made using a kaolin clay powder mixed with water and adjuvant. When preparing the mix, the solution had lumps that were hard to incorporate. Homogeneity was reached eventually after adding kaolin powder gradually, to avoid lump formation. To incorporate the powder into the solution, it had to be mixed longer. Consequently, the adjuvant caused the appearance of bubbles. For a prepared volume of 200 liters, an estimated additional volume of 150 liters of bubbles was formed, reducing the part of the product that could have been used. The bubbles formation also made it harder to see the level when filling the sprayer tank.

The sprayer nozzles weren't clogged by the solution, as kaolin was rarely used. However, when applied at the vineyard scale, there is a risk that the nozzles get clogged due to the thick and abrasive property of the mix. This can cause a technical problem as the solution could be to change the nozzle size between regular and kaolin treatments, being time consuming.

Regarding early defoliation, no specific technical problem was observed. However, it is important to define the degree of defoliation to be reached, or it can result in drastic bunch exposure leading to more sunburn symptoms. The defoliation needs to be moderate to only increase the exposure enough to strengthen the berries. Defoliation also needs to be done at a specific phenological stage to ensure higher sun exposure for newly formed berries. If defoliation is completed too late in the season, it can result in sudden berry sun exposure, leading to higher sunburn symptoms.

Another technical limit linked with early defoliation is the row orientation of the parcel. As the vineyard is composed by differently oriented parcels, it makes it harder to define the defoliation intensity for each parcel.

There is also an uncertainty linked with the worker, leading to more or less leaves left on plants.

Picking berries for quality evaluation was done by different samplers, resulting in a possible bias in results. A solution to reduce this bias could be to only assign one person to sample the integrity of the modalities. However, this solution is time consuming, especially at the scale of two parcels, making it almost impossible to implement.

To limit this bias as much as possible, the company is implementing a specific picking protocol, so that gaps between samplers are minimized.




^{Costs linked with kaolin sprayings}
^{Dose kaolin (kg/ha)}	⁸⁰
^{Price of kaolin per kilo (€/kg)}	^1,6
^{Price of kaolin per hectare (€/ha)}	¹²⁸
^{Spraying time for 0,3 ha (h/0,3)}
^{Cost of sprayer driver per hour (€/h)}
^{Cost of kaolin per hectare (€/ha)}

^{Profits linked with kaolin sprayings}
^{Number of plants per hectare (ha)}	¹⁰⁰⁰⁰
^{Number of bunches per grapevine plant}	^5,35
^{Average weight of a Cabernet Sauvignon bunch (kg)}	^0,15
^{Estimated yield (kg/ha)}	⁸⁰²⁵
^{Damage difference between control and kaolin} (%)	^0,20%
^{Yield gain (kg/ha)}	^16,05
^{Berry mass per bottle of wine (kg/0,75L wine)}	¹
^{Berry mass per litter of wine (kg/L)}	^1,33







^{Profits linked with early defoliation}
^{Number of plants per hectare (ha)}		¹⁰⁰⁰⁰
^{Number of bunches per grapevine plant}		^5,35
^{Average weight of a Cabernet Sauvignon bunch (kg)}		^0,15
^{Estimated yield (kg/ha)}		⁸⁰²⁵
^{Damage difference between control and defoliation} (%)		^0,40%
^{Yield gain (kg/ha)}
^{Berry mass per bottle of wine (kg/0,75L wine)}
^{Berry mass per litter of wine (kg/L)}

In terms of management, the feasibility of both solutions was evaluated to make sure that it could be implemented at the scale of the vineyard.

Overall, kaolin sprayings management at the scale of the study wasn't time consuming. The mix preparation took about 30 minutes for a 200 liters volume. However, if kaolin sprayings are applied at the scale of the vineyard, they will represent additional work and will be harder to manage. The first management limit will concern the use of the sprayers, as they are also used at the scale of the vineyard to perform other tasks such as tillage or canopy trimming during the growing period. Managing how and when the sprayers are going to be used might be time consuming but is necessary to ensure the efficiency of the vineyard work management.

The dose and dates of treatments will also have to be reasoned based on weather conditions, canopy coverage, and workload. It might also represent additional work and time to make sure the conditions are optimal to spray.

Finally, as kaolin must be evenly sprayed on both sides of the canopy, it requires two sprayer passages, increasing the treatment time by 2.

Regarding early defoliation at the scale of the vineyard, the work itself do not represent a management problem. However, it will require hiring seasonal workers to defoliate but will also require the presence of employees to oversee their work.

Overall, for both kaolin sprayings and early defoliation methods, time and workload management represent the main limits in terms of project feasibility.

In order to make sure that using kaolin and early defoliation methods on the vineyard are worth it in terms of loss reduction, an economic study was conducted. The objective of this study was to define if the cost of kaolin and early defoliation would overcome the economic gains linked to sunburn reduction.

The gains were estimated based on the calculated yield difference between the control modality and the other two modalities. The yield gain was then converted in number of produced bottles. As both studied parcels produce Pavillon Rouge wine, the average price of a bottle was calculated based on their selling price.

The results of this study can be found in Table 19 and Table 20, where costs and gains of both methods were reported, based on the latest damage results on both studied parcels.

Table 19: Estimated economic margin made from both studied modalities based on the results on the JBO parcel

Table 20: Estimated economic margin made from both studied modalities based on the results on the L4VS parcel

^{Costs linked with kaolin sprayings} ^{Spraying time for 0,3 ha (h/0,3)} ^{Profits linked with kaolin sprayings} ^{Damage difference between control and kaolin} (%) ^{Yield gain (kg/ha)} ^{Margin (€/ha)}
^{Costs linked with early defoliation} ^{Profits linked with early defoliation} ^{Damage difference between control and defoliation} (%) ^{Yield gain (kg/ha)} ^{Margin (€/ha)}

¹⁰⁰⁰⁰ ^5,35 ^0,15 ⁸⁰²⁵ ^1,80% ^144,45 ¹ ^1,33 ^108,61 ¹²⁵ ^13576,13

According to both tables, the gains linked with sunburn reduction overcome the costs of both studied

methods. Early defoliation seems to be more expansive than kaolin, therefore less profitable for the

Overall, the results show that both methods are profitable when applied at a larger scale. Even if the

damages results on the JBO parcel weren't significant, kaolin sprayings still manage to help gain

However, those results can highly vary based on the vintage weather conditions. Indeed, if the damage

difference between modalities is lower, it could potentially induce economic losses. Moreover, due to

some parcels' orientation, both methods might not work at the scale of the entire vineyard.

Consequently, those results need to be pondered as they highly depend on row orientation and could

vary based on which parcel is studied, the size of the sprayer used, and the planting density.

This study highlighted the effects on sunburn symptoms of two short-term solutions. However,

due to the limited duration of the study, it hasn't been possible to define the impacts of both kaolin and

In order to have been more precise on the organoleptic consequences of kaolin and early defoliation on

Château Margaux's wines, it would have necessitated to continue to conduct this study longer.

If the study had lasted longer, we would have been able to define whether those solutions can be applied

at a large scale in the vineyard, without affecting the typical profile of Château Margaux's wines or not.

conduct Berry tastings could also have been implemented to define the impact of kaolin and defoliation

However, in continuity to this study, the company will vinify the modalities separately, so that they will

be able to conduct tastings to compare the effects of the studied modality on wine organoleptic profile.

Additionally, the study size was limited. The studied plots represented 30 plants per modality per parcel,

which hardly represents the integrity of the parcels. There is consequently an additional uncertainty

Based on the study's results and limits, propositions have been formulated. For each proposition, the objectives, means, costs and risks have been discussed.

To overcome the study duration limit, it can be advised to continue the study on the 2022 vintage. The primary and secondary metabolites analysis will continue until harvest to make sure that no significant differences are observed.

It can also be advised to harvest and vinify separately the modalities of each parcel to produce different wines. When they will be ready, the wines could later be blind tasted and compared to one another to define if there is a significant organoleptic difference between the three studied modalities. If there aren't, then it means that both solutions can successfully be applied to the integrity of the vineyard, without affecting the typicity of Château Margaux's wines.

The 2022 study wasn't the first conducted on grape sunburn by Château Margaux but is part of a longterm project to reduce grape sunburn at the scale of the vineyard. It can therefore be advise to prolongate the study to the 2023 and 2024 vintages in order to make sure that kaolin and early defoliation work on different types of climates.

To continue and perfect the study on grape sunburn, it can be advised to reconduct the study for the next growing seasons, by improving the experimental set-up. The objective of this proposition is to increase the study precision and improve the knowledge and management capacities linked with sunburn solutions.

To do so, the study could be applied at a larger scale of the vineyard, on different grape varieties and parcels orientations. By also choosing more reference plants per modality to study, it will increase the representativity of the results at the scale of the vineyard.

Moreover, the intensity of both methods can be modulated, and trials can be conducted. For example, different defoliation intensities could be tested as different modalities, based on the parcels' orientations. For kaolin sprayings, it could be advised to test different concentrations based on weather conditions. By doing so for a few years, the applied dose can be modulated so that time management becomes optimal.

The cost of this proposition will be close to this year's study cost, but the investment return will be larger as it should help at a long-term scale to significantly reduce/avoid berry sunburn.

The only risk linked with this proposition is the absence of sunburn linked with bad weather conditions, and therefore the inability to evaluate the efficiency of the studied methods.

Based on the positive results of the studied, it can be proposed to extend the solutions at the scale of the vineyard. While early defoliation results mainly depend on row orientation, kaolin sprayings can be easily applied at the scale of the vineyard independently from row orientation.

The objective of this proposition is to reduce sunburn at the scale of the vineyard, and reduce economic losses linked with this issue.

To implement this proposition, visual observations will have to be done to define which parcels need to be treated with kaolin. Based on the results, a kaolin mix will be prepared and sprayed depending on weather conditions.

The cost of this proposition will be estimated at 13 614,02€/ha, what kaolin sprayings cost for this study multiplied by the number of hectares of the vineyard (94ha). Regarding the investment return of this proposition, it can be estimated as the return obtained with the kaolin sunburn study multiplied by the number of hectares treated (= at least 13 614,02€/ha).

However, the risk of this proposition is that kaolin sprayings might not work as well on the integrity of the vineyard as they worked on the two studied Cabernet Sauvignon parcels. It can be imagined that other grape varieties are less sensitive to sunburn, and that the investment return will be less important,

if not negative. In order to overcome this risk, it can be advised to first continue and improve the experimental set-up at a larger scale before extending it at the scale of the vineyard.

To overcome technical limits linked with kaolin sprayings and early defoliation, technical resources propositions have been formulated.

For kaolin sprayings technical limits, filters can be included in the sprayers to limit the risk of nozzle clogging. Rather than having to change nozzles before each treatment, implementing filters is less time consuming, as they can be left for regular treatments too.

Regarding the adjuvant bubbling property, it is linked with air incorporation during the mixing process. To overcome this issue, it can be advised to reduce the mixing speed and to incorporate kaolin into the mix slower and in lower quantities.

To overcome technical problems linked with early defoliation at the scale of the vineyard, two propositions can be made. The first one being to conduct a trial on defoliation based on row orientation, in order to link ideal defoliation intensity with sun exposure. The second proposition is to provide the correct formation for seasonal workers so that they understand the degree of defoliation that is supposed to be reached, reducing problems linked with intense defoliation.

Managing time and workload is essential to continue this study or apply it at a larger scale. As seen previously (7), kaolin sprayings as well as early defoliation solutions need to be correctly managed.

Based on the vineyard workload, sprayers and workforce might not be available to perform kaolin sprayings during the growing season. Consequently, two solutions exist. Either the vineyard manager can decide to reduce time allocated with other tasks such as tillage or canopy trimming, and prioritize kaolin sprayings in the work calendar, either kaolin sprayings can be performed by external workers. While the first solution seems more complicated in terms of time management, it is less costly as it doesn't necessitate to spend additional money by hiring workforce and lending material. In comparison, there are no direct economical losses linked with tillage and canopy trimming, even if they are essential to perform, while economical losses linked with sunburn are significative.

To manage the dose and dates of treatments, different solutions can be implemented. First, the weather conditions of the season will need to be followed. If long high-temperature episodes are predicted, a kaolin treatment must be done in prevention. Then, observations can be performed at the scale of the vineyard based on weather conditions, to verify if kaolin has been washed out of the canopy depending on rainfall events. The dose of treatment will also depend on the weather conditions. If high temperature periods are predicted before a rain episode, then the dose could be divided by 2, as it is expected to be washed out and renewed after rain. Kaolin treatment management should therefore be as precise as possible, to ensure higher protection of the vineyard.

Finally, managing early defoliation will necessitate hiring and overseeing seasonal workers, representing additional money and work. However, vineyard employees are usually already busy completing other tasks, and do not have time to oversee early defoliation. Like for kaolin sprayings, solutions include reducing time allocated with other tasks to free some time for defoliating or hire external workers to complete their tasks while they oversee early defoliation.

To continue the study on grape sunburn, other types of experiments could be conducted such as evaluating the consequence of different inter-row cover crops on grape sunburn.

Cover crops can absorb an important part of solar radiation (Varlet-Grancher et al., 1989). Consequently, when implemented in the vineyard's inter-rows, it can reduce part of the reflected solar radiation, diminishing direct reflection on bunches of grapes.

To do so, different types of cover crops should be implementing at the scale of the vineyard, and measures should be conducted in order to evaluate their reflection degree, and therefore their impact on sunburn.

In terms of budget, this trial will have costs linked with the purchase of specific seed mixes, soil preparation and cultivation, as well as tools used to evaluate reflected radiation. However, if the study significantly diminishes canopy temperature by finding the ideal inter-row cover crops, the investment return could be important.

Nevertheless, this solution only works on specific types of soils. If the soil type is lighter than the cover crop, then it is useful to implement it, as the nude soil's solar radiation reflection will increase radiation received by the canopy.

Moreover, this solution has limits. Implementing cover crops could potentially result in higher competition between the grapevine and the crops in terms of soil nutrients.

Climate change will bring new challenges to wine production. The 2022 vintage is a good example of this hypothesis, as long heatwave episodes caused severe drought and grape sunburn, affecting both the yield and quality of the production.

In order to overcome the future effects of climate change, institutional changes seem necessary. For instance, the evolution of the appellations' system to include technical and agronomical innovations is inevitable to limit losses and quality changes linked with climate change. It can therefore be imagined that the PDO specifications as well as the national legislation will evolve to allow for instance shade netting and vineyard irrigation up to a certain level at the scale of the Médoc vineyard. Insurance systems for environmental induced losses (such as frost and hail) could also be implemented to strengthen the vineyards capacity to face climate change.

However, if the PDO specifications do not evolve in the next few years, it can be advised that Château Margaux should stop being part of the PDO and start using alternative methods to limit the consequences of climate change without affecting their wine typicity. Thanks to their renown, Château Margaux won't necessarily be affected in terms of sales and profits by their declassification, due to their already existing notoriety.

Conclusion

The study was conducted on two parcels of Cabernet Sauvignon grapevine and highlighted the reduction of sunburn symptoms on both the kaolin-sprayed modality, as well as on the early defoliation modality, while being exposed to high temperatures and solar radiation. This study meets the need of Château Margaux to find short-term solutions against grape sunburn, waiting to be able to reorient their parcels.

The 2022 vintage has been hot and dry, favorable to grape sunburn. There has been less rainfall in 2022 than in 2021, resulting in a higher canopy porosity, and exposing more bunches to solar radiation.

On average, the kaolin-spraying solution helped to decrease by 90% the symptoms on the bunches of grapes, meanwhile the early defoliation solution decreased sunburn by 86% by the end of the growing season. The sunburn observation as well as the bunch temperatures model brought to light that the kaolin particle film is efficient on the canopy whenever the temperatures exceed 30°C. In this condition, sunburn symptoms start to appear, and bunch temperature rises above 40°C. It also brought to light that early defoliation can increase bunch temperature by diminishing the bunch coverage, without significantly increasing its sunburn symptoms.

Thanks to the calibration model and the manually taken infrared temperatures, we have observed a significantly cooling effect of kaolin on both bunches and leaves. We can therefore establish a link between the sunburn protection and the bunch/leaves temperatures reduction.

Globally, grapevine physiology doesn't seem to have been negatively impacted by kaolin and early defoliation during the 2022 vintage, even under the constraining weather conditions. Indeed, we can even highlight that the kaolin particle film has had a positive effect on the thermo-radiative stresses of the plant, as well as on its water efficiency.

On the contrary, the early defoliation modality increased the plant's stresses by increasing its porosity, but still managed to reduce the symptoms of sunburn on bunches, by increasing its synthesis of metabolites.

Regarding the berries, it doesn't seem that kaolin and early defoliation affected their quality negatively, as the results weren't significant. Both alternatives could be a potential short-term solution to tackle the issue of grape sunburn, as they do not seem to affect the organoleptic quality of the harvest. However, Château Margaux should continue this study by implementing berry and wine tasting between modalities to make sure both modalities do not affect the wine organoleptic profile.

This study emphasizes promising results for both kaolin and early defoliation against sunburn, after three years of test on the vineyard. Nevertheless, the use of both methods needs to be evaluated in the long run to make sure that it won't affect the physiology of the vineyard, in the context of the Château Margaux's terroir.

In a context of climate change, where drought events and heat waves are becoming more recurrent, the 2022 vintage happened to be a good example of how global warming can affect grape production and helped us justify the relevance of using alternative methods to reduce its effects.

Therefore, to continue this study, we would advise choosing parcels with other grape varieties and/or orientations, to verify that both methods will work in any situation within the vineyard. Additionally, it could be interesting to modulate the kaolin sprayings, by reducing the dose but increasing the number of applications for the vintages with higher rainfall.

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Relative humidity Measure of water vapor in air as a percentage of the amount needed

Figure 1: Observed symptoms of low-intensity (left) and high-intensity (right) sunburn at Château

Figure 3: Map of the Bordeaux vineyard, and location of the Margaux appellation (red box) (CIVB,

Figure 4: Wines produced and sold by Château Margaux (Château Margaux, 2022) 19

Figure 6: Scheme of the experimental plan of Les 4 Vents Sable, including the repartition of the

Figure 7: Scheme of the experimental plan of Jean Brun Ouest, including the repartition of the modalities

Figure 8: Photograph of Cabernet Sauvignon leaves before (on le left) and after (on the right) the first

Figure 11: Evolution of the maximum, minimum and average temperatures as well as the rainfall for the 2022 growing season, from March the 1^st until August the 22^nd, based on the Enclos weather station

Figure 12: Comparison of the 10°C base temperature sum for the last 5 growing seasons, from March

the 1st to August the 22th, based on the Margaux Sencrop weather station data 41

Figure 13: Evolution of predawn leaf water potential for both studied parcels 43

Figure 15: Leaf temperature per modality for both parcels, taken with an infrared thermometer, between

Figure 16: Comparison of temperature data between 20 potential usable HOBO captors, on the 2^nd and

Figure 17: Comparison of light data between 20 potential usable HOBO captors, on the 2nd and 3rd of

Figure 18: Comparison of temperature data between 10 potential usable TinyTag captors, on the 23^rd

Figure 19: Comparison of relative humidity data between 10 potential usable TinyTag captors, on the

Figure 20: Tinytag captors temperature and humidity results on the JBO parcel between July the 17th

Figure 21: Comparison of average bunch temperature per modality at different times of the day, on the sun-exposed side of the canopy, taken by an infrared manual thermometer, between June the 13^th and

Figure 22: Multiple linear regression model from XLSTAT between the IR thermometer bunch temperature and the HOBO captor recorded light and temperature data for the control modality in the

Figure 23: Evolution of bunch temperature on the JBO parcel between the 17th and the 19th of June

Figure 24: Evolution of bunch temperature on the JBO parcel between the 12th and the 15th of July

Figure 25: Evolution of bunch temperature on the JBO parcel between the 10th and the 12th of August

Figure 26: Evolution of bunch sunburn frequency and intensity on JBO and L4VS, from June the 22nd

Figure 27: Evolution of damages linked with sunburn on bunches per modality, from June the 22^nd to

Figure 28: Evolution of leaf sunburn frequency and intensity on JBO and L4VS, from June the 22nd to

Figure 29: Evolution of damages linked with sunburn on leaves per modality, from June the 22^nd to

Figure 30: Evolution of mass and volume of 100 berries between July the 21st and August the 22nd, for

Figure 31: Analysis results of berry maturity per modality, between July the 21st and August the 22^nd,

Figure 32: External laboratory analysis results of anthocyanins and phenolic compounds per modality,

Table 1: Viticultural climates classification based on the Huglin Index (Tonietto and Carbonneau, 2004;

Table 2: Comparison of the number of days where the maximum temperature (Tmax) was higher than 30°C, for the last 5 growing season, from March the 1^st to August the 22^th, according to the Margaux

Table 4: Results of the LSD Fisher Test on Enhanced Vegetation Indexes (EVI) of the different

Table 5: Results of the LSD Fisher Test on Enhanced Vegetation Indexes (EVI) of the different

Table 6: Results of the LSD Fisher Test on Leaf Area Indexes (LAI) of the different modalities in the

Table 7: Results of the LSD Fisher Test on Leaf Area Indexes (LAI) of the different modalities in the

Table 8: Results of the LSD Fisher Test on August the 11th Stem Water Potentials (SWP) of the different

Table 9: Results of the LSD Fisher Test on August the 11^th Stem Water Potentials (SWP) of the different

Table 10: Results of the LSD Fisher test on leaf temperature of the different modalities in the JBO parcel

Table 11: Results of the LSD Fisher test on leaf temperature of the different modalities in the L4VS

Table 12: Results of the LSD Fisher test on bunch temperature of the different modalities in the JBO

Table 13: Results of the LSD Fisher test on bunch temperature of the different modalities in the L4VS

Table 18: Evolution of the bunch number per parcel before and after thinning operations 52

Table 14: Results of the LSD Fisher test on berry sunburn damages of the different modalities in the

Table 15: Results of the LSD Fisher test on berry sunburn damages of the different modalities in the

Table 16: Results of the LSD Fisher test on leaf sunburn damages of the different modalities in the JBO

Table 17: Results of the LSD Fisher test on leaf sunburn damages of the different modalities in the L4VS

Table 19: Estimated economic margin made from both studied modalities based on the results on the

Table 20: Estimated economic margin made from both studied modalities based on the results on the

Annexes

- Macroclimate: the climate of a region, generally described by weather stations data. Is independent of local topography, soil type, and vegetation but is determined by the geographic location. The macroclimate usually can extent over hundreds of kilometers and defines a particular grape growing region, such as Bordeaux.

- Mesoclimate: the climate of a site or large vineyard. It varies from macroclimate as it takes into consideration topography and can extent up to several kilometers.

- Microclimate: the climate within a vineyard. This climate depends on the vineyard cultural

practices and can vary by a few centimeters due for example to the presence of leaves.

Annex 2: Interview of Julien C., Vineyard Manager of Château Margaux, in French, on the 19^th of July 2022

Célia M. : Bonjour Julien. Dans le cadre de mon mémoire de fin d'études, je vais vous poser des questions sur différents thèmes, dans l'objectif de mieux comprendre la typicité du vin produit, et les effets du changement climatique sur vos méthodes de production et de management.

Pour commencer, que fait, à votre avis, la typicité du produit du Château Margaux, justifiant sa valeur économique ?

Julien C. : Je dirai que la typicité des vins de Margaux et du domaine provient surtout de leur terroir. On a la chance d'avoir 60 unités pédologiques différentes, avec trois types de terrasses différentes, qui forcément apportent un assemblage beaucoup plus complexe que les domaines voisins qui n'ont pas forcément d'argilo-calcaire et d'autres terroirs que seulement nous avons sur l'appellation.

Célia M. : Quelles actions au vignoble justifient pour vous le plus la qualité des raisins ?

Julien C. : L'intégralité des tâches. A Château Margaux, toutes les tâches sont réalisées à la main, c'est du travail d'orfèvre. Chaque vigneron s'occupe de ses parcelles qui représentent à peu près 30 000 pieds et ça les rend responsables et « propriétaires » de la parcelle, et y apportent donc plus d'attention que du travail en équipe ou de prestation.

Célia M. : Quelles variables au vignoble vous font choisir une parcelle plutôt qu'une autre pour un certain type de vin ? Par exemple, comment évaluez-vous qu'une certaine parcelle entrera une année dans le grand vin, puis la suivante dans le générique ?

Julien C. : La première des choses ce sont les études pédologiques où chaque fois qu'il y a une parcelle d'arrachée on effectue une fosse pédologique pour vraiment identifier le terroir, ou les terroirs différents de la parcelle. La deuxième chose c'est la chance qu'on a ici d'avoir des bases de données énormes depuis 100/200 ans où chaque maître de chai, chaque chef de culture, chaque responsable d'exploitation a noté à un moment donné où la parcelle irait dans les différents vins.

Célia M. : Quels sont les facteurs de production fixes au vignoble que vous estimez ne pas pouvoir changer pour continuer de produire ces vins, malgré l'évolution des tendances de consommation et le changement climatique ?

Julien C. : Changer de cépage veut dire changer la typicité des vins de Margaux et du Médoc. On a la chance par rapport à Saint Emilion d'avoir un encépagement majoritairement Cabernet Sauvignon qui fait des degrés d'alcool encore tout à fait raisonnables comparés à du Merlot, qui monte rapidement à 15-16° dans les années les plus chaudes, alors que lorsqu'on monte à 13,5-14° pour du Cabernet Sauvignon c'est déjà le grand maximum. Changer de cépage pourrait être mal vu par les consommateurs qui ne retrouveraient pas l'identité d'un vin médocain et de surcroit d'un vin de Château Margaux. Adapter les pratiques agronomiques sur l'orientation des rangs pourquoi pas. Mettre en place de l'irrigation, tant que les instances de l'INAO nous disent pas que c'est ok dans des décrets

d'appellation, ce sera compliqué. Au niveau pratiques agronomiques, il y a des choses à faire sur les semis temporaires de couverts végétaux, sur les pratiques d'échardage, d'effeuillage, sur la résistance des porte-greffes à la sécheresse car certains résistent mieux que d'autres. Mettre plus de sélection massale que de clonale pour avoir une diversité génétique. Il y a donc encore des choses à faire au vignoble.

Célia M. : Quelles conséquences ce changement aura-t-il sur vos pratiques, si vous estimez qu'il aura un impact ?

Julien C. : Les conséquences seront multifactorielles, le Médoc est une presqu'île, c'est un isthme, et on aura forcément un jour la Gironde qui va monter encore plus haut que ce qu'elle n'est déjà. Il va sûrement y avoir des terres qui vont être perdues. Ensuite, il faudra trouver des solutions autres qu'agronomiques tels des filets de protection pour amener de la vendange la plus saine et la plus qualitative.

Célia M. : Pourriez-vous envisager l'incorporation de pratiques comme l'effeuillage ou le kaolin dans l'agenda des travaux de la vigne, ou cela posera-il un soucis par rapport à la charge de travail des vignerons à cette période ?

Julien C. : L'effeuillage pourrait être incorporé s'il est fait au bon stade phénologique ; nouaison / début fermeture. Après c'est trop tard car la grappe n'a pas le temps de s'adapter aux coups de chaud. Le kaolin pourquoi pas s'il n'y a pas de modifications des paramètres organoleptiques des vins. Employer du calcaire pur type Megagreen qui possède près de 40% de calcaire et les processus silices qui sont aussi importants pour rendre les feuilles plus résistantes à la chaleur.

Cela posera forcément problème par rapport à la charge de travail car ces produits ne sont pas forcément miscibles avec nos traitements actuels dont nécessiteraient une charge de travail supplémentaire.

Célia M. : Quels seraient les limites ou challenges d'implémenter ces solutions en termes d'expertise, de procédés, et de main d'oeuvre ?

Julien C. : Dans l'ordre, les limites sont : 1. Les hommes, 2. Les moyens (tracteurs), 3. Climato, 4. Les travaux qui sont gérés en même temps. En termes de main d'oeuvre, cela impliquerait des charges de travail supplémentaires et donc potentiellement l'embauche d'intérimaires.

Célia M. : Quels sont pour vous les risques directs du changement climatique sur le vignoble de Château Margaux ?

Julien C. : Il y aura forcément des impacts au niveau qualitatif car on aura des baies qui auront un goût de cuit, et il faudra faire plus de nettoyage de grappes dans les éclaircissages. Il faudra donc adapter nos pratiques agronomiques au changement climatique.

Célia M. : Serait-il envisageable dans les années à venir de changer l'encépagement du vignoble pour y implémenter des variétés plus résistantes aux stress hydrique et thermique ?

Julien C. : La principale personne à convaincre serait la propriétaire, car si elle n'est pas d'accord pour ce type de changement, on ne fera pas grand-chose.

Célia M. : Depuis combien d'années environ observez-vous de l'échaudage sur les vignes du Château Margaux ?

Julien C. : Combien d'années c'est difficile à dire mais tous les millésimes où on a eu des coups de chaud ; 2003, 2005, 2011, 2018, 2020 et 2022. Ce sont que des millésimes où on a eu des pics de chaleur qui causent des symptômes d'échaudage.

Célia M. : L'échaudage représente-t-il un risque significatif pour votre production ? Julien C. : Sur le rendement oui.

Célia M. : Jusqu'où estimez-vous pouvoir aller en production viticole pour éviter l'échaudage et conserver un volume et une qualité de vin suffisants ?

Célia M. : C'est tout pour moi, je vous remercie pour le temps que vous m'avez accordé et vous souhaite une bonne fin de journée !

Julien C. : Avec plaisir, n'hésitez-pas à me contacter si vous avez des questions supplémentaires.

Annex 3: Soil map for the different parcels of Château Margaux, based on soil analyses, 2015

Annex 4: Repartition of the grape varieties in the vineyard of Château Margaux, and its reference blocks

Annex 5: Organigram of the company summarizing the different services and managerial levels

Annex 6: Map of Château Margaux's parcels and their row orientation, in red the studied parcels

Annex 7. Photographs of the kaolin mix preparation in the Mixbox, and of the sprayer used




					^{Kaolin spraying preparation}			^{Real product usage}
	^{Dose (kg/ha)}	^Application	^Mix	^L4VS	^JBO	^Total	^L4VS	^JBO	^Total
^14/06/2022	²⁰	^2*10kg	^{Water (L)}	^93,33	^106,67	²⁰⁰	^43,16	^47,26	^90,42
^14/06/2022	²⁰	^2*10kg	^{Kaolin (kg)}	^6,22	^7,11	^13,33	^2,88	^3,15	^6,03
^14/06/2022	²⁰	^2*10kg	^{Adjuvant (mL)}	^18,67	^21,33	⁴⁰	^8,632	^9,452	^18,08
^07/07/2022	²⁰	^2*10kg	^{Water (L)}	^93,33	^106,67	²⁰⁰	^43,16	^47,26	^90,42
^07/07/2022	²⁰	^2*10kg	^{Kaolin (kg)}	^6,22	^7,11	^13,33	^2,88	^3,15	^6,03
^07/07/2022	²⁰	^2*10kg	^{Adjuvant (mL)}	^18,67	^21,33	⁴⁰	^8,632	^9,452	^18,08
^22/07/2022	¹⁰	^2*5kg	^{Water (L)}	^93,33	^106,67	²⁰⁰	^43,16	^47,26	^90,42
^22/07/2022	¹⁰	^2*5kg	^{Kaolin (kg)}	^3,13	^3,57	^6,7	^1,44	^1,575	^3,015
^22/07/2022	¹⁰	^2*5kg	^{Adjuvant (mL)}	^18,67	^21,33	⁴⁰	^8,632	^9,452	^18,08
^29/07/2022	¹⁰	^2*5kg	^{Water (L)}	^93,33	^106,67	²⁰⁰	^43,16	^47,26	^90,42
^29/07/2022	¹⁰	^2*5kg	^{Kaolin (kg)}	^3,13	^3,57	^6,7	^1,44	^1,575
^29/07/2022	¹⁰	^2*5kg	^{Adjuvant (mL)}	^18,67	^21,33	⁴⁰	^8,632	^9,452
















^Parcel	^{28.0-2 Les 4 Vents Sable}	^{85 Jean Brun Ouest}
^{Surface of one block (6} + ^{2 1/2 ranks) (ha)}	^0,05	^0,05
^{Modality surface (3 blocks) (ha)}	^0,14	^0,16
^{Number of passages per treatment}	^1,00	^1,00

Annex 10. Photographs of the Scholander pressure chamber used to measure water potentials

Annex 11: Evolution of the maximum, minimum and average temperatures as well as the rainfall for the 2022 growing season, based on the Plateau weather station

Annex 12: Key phenological stages for the last 4 growing seasons for both studied parcels

			Key phenological stages
			Mid-bud burst	Mid-flowering	Mid-ripening
Parcel	Les 4 Vents Sables	2022	09/04	22/05	31/07
		2021	29/03	03/06	07/08
		2020	08/04	22/05	28/07
		2019	31/03	01/06	08/08
	Jean Brun Ouest	2022	11/04	24/05	31/07
		2021	29/03	04/06	06/08
		2020	09/04	21/05	25/07
		2019	08/04	06/06	07/08

Annex 13: Map of JBO's enhanced vegetation index values for each grapevine plant, Vineview

Annex 14: Map of L4VS' enhanced vegetation index (EVI) values for each grapevine plant, Vineview

Annex 15: Tinytag captors temperature and humidity results on the L4VS parcel between July the 17th and the 19th

Annex 16: Multiple linear regression model from XLSTAT between the IR thermometer bunch temperature and the HOBO captor recorded light and temperature data for the kaolin modality in the Jean Brun Ouest parcel

Annex 17: Multiple linear regression model from XLSTAT between the IR thermometer bunch temperature and the HOBO captor recorded light and temperature data for the early defoliation modality in the Jean Brun Ouest parcel

Annex 18: Multiple linear regression model from XLSTAT between the IR thermometer bunch temperature and the HOBO captor recorded light and temperature data for the control modality in the Jean Brun Ouest parcel

Annex 19: Multiple linear regression model from XLSTAT between the IR thermometer bunch temperature and the HOBO captor recorded light and temperature data for the kaolin modality in the Les 4 Vents Sable parcel

Annex 20: Multiple linear regression model from XLSTAT between the IR thermometer bunch temperature and the HOBO captor recorded light and temperature data for the early defoliation modality in the Les 4 Vents Sable parcel

Annex 21: Analysis of bunch temperature evolution on the JBO parcel for the 2022 growing season heatwaves

For the L4VS parcel, the followed bunches of grapes are exposed on the West part of the canopy and reach a temperature peak between 3 and 5 PM.

During the June heat wave, the bunches reached a maximum of 42,9°C for the kaolin modality, 46,9°C for the early defoliation modality, and 43,9°C for the control modality. During the July heat wave before véraison, the bunches maximum temperatures were: 40,5°C for the kaolin modality, 44°C for the early defoliation modality, and 41,8°C for the control modality. In the August heat wave during maturation, the bunches reached a maximum temperature of 39,4°C for the kaolin modality, 46,3°C for the early defoliation modality, and 44,9°C for the control modality.

The difference between the highest bunch temperature of the kaolin and the control modalities was on average between 1,01°C and 5,5°C for the JBO parcel. Consequently, it can be concluded that for the JBO parcel, kaolin sprayings helped significantly reduce bunch temperature.

Annex 22: Evolution of mass and volume of 100 berries between July the 21st and August the 22nd, for the JBO parcel

Overall, between July the 21^st and August the 22^nd, it can be observed that the mass and volume of the kaolin modality berries are more important than the other modalities.

On the 22^nd, the kaolin modality 100 berries weight was more than 30 grams higher than the control modality, while their volume was 0,2 mL more important. Regarding the early defoliation modality, the berry mass and volume was closer to the control modality, than to the kaolin.

Consequently, on both parcels, kaolin significantly improved berry physiology, while early defoliation slightly improved it.

Annex 23: Excell laboratory analysis results by modality, for the Xth of July, and the 10th of August

Annex 24: Analysis results of berry maturity per modality, between July the 21st and the 22^nd of August, for the JBO parcel

Based on the modelized graphs, the differences in pH, sugar, total acidity, and malic acidity levels between modalities on the JBO parcel aren't significatively different between modalities.

On July the 29^th, the acidity of the control modality was slightly more important while the pH was lower, but by the end of the maturity (August the 22^nd), the values stabilized to reduce the gap between modalities.

Overall, it can be concluded that neither the kaolin nor the early defoliation modalities significantly affected berry primary metabolites.

Annex 2: Interview of Julien CAZENAVE, Vineyard Manager of Château Margaux, in French, on the 19^th

Annex 3: Soil map for the different parcels of Château Margaux, based on soil analyses, 2015 89

Annex 4: Repartition of the grape varieties in the vineyard of Château Margaux, and its reference blocks 90

Annex 5: Organigram of the company summarizing the different services and managerial levels 91

Annex 6: Map of Château Margaux's parcels and their row orientation, in red the studied parcels 92

Annex 7: Photographs of the kaolin mix preparation in the Mixbox, and of the sprayer used 93

Annex 10: Photographs of the Scholander pressure chamber used to measure water potentials 94

Annex 11: Evolution of the maximum, minimum and average temperatures as well as the rainfall for the

Annex 12: Key phenological stages for the last 4 growing seasons for both studied parcels 95

Annex 13: Map of JBO's enhanced vegetation index values for each grapevine plant, Vineview 96

Annex 14: Map of L4VS' enhanced vegetation index (EVI) values for each grapevine plant, Vineview 97

Annex 15: Tinytag captors temperature and humidity results on the L4VS parcel between July the 17th and

Annex 21: Analysis of bunch temperature evolution on the JBO parcel for the 2022 growing season

Annex 22: Evolution of mass and volume of 100 berries between July the 21st and August the 22nd, for the

Annex 23: Excell laboratory analysis results by modality, for the Xth of July, and the 10th of August 102

Annex 24: Analysis results of berry maturity per modality, between July the 21st and the 22^nd of August, for