Charles Obiero* and Markus Keller
*Washington State University, 24106 N Bunn Rd, Prosser, WA, 99350 (charles.obiero@wsu.edu)

Frequent drought episodes during fruit development threaten sustainable production of premium winegrapes in the western United States. During an extreme drought event, the irrigation water supply to vineyards may be shut off and growers often remove fruit to ensure vine survival. This study investigated the idea that fruit removal during drought enhances vine survival in Cabernet Sauvignon and Riesling. In 2022 and 2023, irrigation water was shut off either at fruit set or at veraison, and 0, 50, or 100% fruit was removed at the start of each drought period. The outcomes were compared with standard regulated deficit irrigation (RDI), with and without fruit removal. Drought from fruit set or veraison lowered the vines’ water status alike, and the effect was greater in vines with no fruit removed in both cultivars. Canopies of vines exposed to drought stress from fruit set were up to 5.6°C warmer than the RDI vines. Drought starting at fruit set depressed yield more than drought starting at veraison in both cultivars. Vines exposed to drought from fruit set had more than 45% (Riesling) or 60% (Cabernet Sauvignon) less yield than RDI vines. Drought and fruit removal had no clear influence on fruit composition. Compared to the RDI vines, there was more than a one-third reduction in early-season shoot growth and a 40 to 50% drop in the number of flowers in vines exposed to drought stress the previous year, even if fruit had been removed from those vines. Our findings demonstrate that extreme drought will have a long-lasting effect on vine growth and productivity, regardless of fruit removal.

Funding Support: USDA Northwest Center for Small Fruits Research