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.

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

Introduction

1. Climate change and its impact on grape sunburn