Kaolin treatments on Pinot noir grapevines for the control of heat stress damages

he aim of the study was to verify if vineyard kaolin application during the 2017 hot summer could reduce the negative effects of high temperatures and heat stress on canopy physiological processes, yield and fruit quality. The kaolin was applied once at the beginning of August, at 3% concentration, in a Pinot Noir vineyard. The application was performed only to the west side of the rows, where the vines were more subjected to heat stress. The 2017 summer was very hot, with maximum air temperature higher than 35 °C for several consecutive days in June, July and August and with heat waves that reached 42.3 °C in August. The kaolin coating works by significantly reducing leaf temperatures in comparison to untreated vines, with an average of about − 4 °C and up to −6 °C. Moreover, it maintains high the photosynthetic activity preventing irreversible photoinhibition phenomena, whereas untreated vines exhibit a marked physiological damage with chlorotic and necrotic leaves, dehydrated berries and sunburn damages. At harvest, 30-35% of the untreated vines were affected by severe water stress symptoms and produced unmarketable fruits. In comparison to the untreated vines, those sprayed with kaolin showed a higher yield (+27%), higher anthocyanins (+35%) and higher concentration of organic acids (+11%)