Sunscreen for Grapevines: Kaolin Clay Use in Pacific Northwest Vineyards
Cody Copp,* Aidan Wiggins, and Melinda Cramp
*Oregon State University, 418 N Main Street, Milton-Freewater,
OR, 97862 (cody.copp@oregonstate.edu)
Short-term climate change effects like extreme heat threaten grape production in the Pacific Northwest. Extreme temperatures inhibit photosynthesis, reduce yield, delay ripening, and promote fruit sunburn. Kaolin clay is used in other crops to reduce heat stress and sunburn. Additionally, other labeled (insect suppression) and experimental (wildfire smoke exposure) uses distinguish kaolin as a viticultural tool to mitigate climate change-related risks.
Multiple field experiments were established in 2022 and 2023 in commercial vineyards near Milton-Freewater, Oregon to optimize kaolin application (i.e., rate, timing, adjuvant use), observe fruit sunburn effects, and measure effects on leafhopper populations. In one block of Vitis vinifera L. cv. Syrah, kaolin was applied between fruit set and harvest at varying rates (0, 11, 22, or 45 kg/ha), at different times (pre- and postveraison), and with commercial adjuvants. The effect on sunburn was tested with fruit zone leafing on the afternoon side of Syrah and Tempranillo vines with label rate kaolin application to half of clusters prior to a postveraison heat event (three days above 41°C). At a second site, kaolin was applied to organic Cabernet Sauvignon and populations of Erythroneura elegantula adults and nymphs were monitored from bloom until harvest.
In 2022, kaolin at 45 kg/ha improved stomatal conductance above Ψleaf of -1.4 mPa, increased fruit yield by 5%, and slightly improved anthocyanin concentration. In 2023, tannin and anthocyanin concentrations increased with application rate and were greater with preveraison application. Visual assessment indicated that all adjuvants dramatically improved dispersion and deposition of kaolin on berries. Application prior to a heat event reduced the impact of sunburn on marketable yield and quality; treated clusters had 52 to 85% fewer shriveled berries and up to 25% higher anthocyanin concentration. Kaolin application reduced the peak population of second generation E. elegantula nymphs by 54%.
Funding Support: Agricultural Research Foundation, Oregon Wine
Research Institute
