Assessment of the Heat-Stress-Mitigating Effect of Kaolin in Grapevine: A Comparative Study in Two Vineyards

Climate change is intensifying summer stress conditions, with significant impacts on vine physiology and grape production. Kaolin is commonly used to mitigate heat stress, though its effectiveness may vary depending on vineyard conditions. This study aimed to compare the effects of kaolin application (K) with an untreated control (C) on Verdicchio grapevines across two distinct vineyard sites differing in environmental conditions over two consecutive growing seasons, focusing on leaf gas exchange, leaf temperature, grape composition and yield, and wine characteristics. Results showed that the effects of kaolin varied between sites. Under high thermal stress and low vine vigor, kaolin application improved gas exchange, sustained higher photosynthetic rates, and reduced leaf temperature. Conversely, in higher-vigor vineyards, the effects were less pronounced and mainly limited to reductions in leaf temperature. Under low-vigor conditions, K resulted in higher berry weight and lower total soluble solids. Wines from kaolin-treated grapes exhibited slightly reduced alcohol content and pH. These findings suggest that kaolin’s effectiveness is strongly influenced by climatic conditions and vine vigor. In Mediterranean regions, where heatwaves and drought are common, kaolin application may be a promising tool to alleviate heat stress, supporting improved grape yield and composition.