Kaolin foliar application for the vineyard summer heat stress mitigation

In the context of ongoing climate change, this study aimed to evaluate the physiological and productive responses of two white grape cultivars, Carricante and Grillo, to the application of natural protective compound against excessive temperature and radiation. The trial was conducted during the summer 2023, in a commercial vineyard located on the Eastern slope of Mount Etn a (Sicily island, south Italy). At the stage berries groat-size, vines were treated with kaolin (a white clay at 2%). A monthly monitoring was performed, until grape harvest, measuring leaf gas-exchanges and leaf water potential. At harvest, the yield and its traits were measured. Under Mediterranean stressed situation, the application of kaolin preserves the photosynthetic activity in the leaves and saves water, with different intensity depending on the cultivar. The ripening stage can be delayed with beneficial effect on maintaining higher level of titratable acidity and lower soluble solids accumulation. These latter finding is of practical interest in areas most subjected to global warming because counteract the berry shrivelling and the high concentration of the soluble solids in the grapes and consequently allows to obtain wines with low alcohol content, often preferred by the modern consumers. Finally, kaolin is easy to apply, quite cheap and very flexible since it can be used only if necessary, when the air temperature exceeds 35°C for at least 2-3 consecutive days.