Annegret Cantu,* Hildegarde Heymann, James Campbell, Martina Galeano, Luis Sanchez, Nick Dokoozlian, Ann-Dorie Romania Webley, Larry A Lerno, Susan Ebeler, Andrew McElrone, S Bagshaw, and Elizabeth Jane Forrestel
*UC Davis Viticulture & Enology, One Shields Avenue, Davis, CA, 95618
(acantu@ucdavis.edu)

Heatwaves, defined as three or more consecutive days above average historic maximum temperatures, significantly impact agricultural crop yields and quality, especially in arid or semiarid regions with reduced water availability during the growing season. In grapevine, excessive heat can lead to crop loss and reduce the quality of berries and the resulting wine. The primary means of mitigating damage from heatwaves is by applying excess irrigation water before and during the heatwave event, thus promoting evaporative cooling by the plant and reducing soil temperatures in the rooting zone and surface. California winegrowing regions, among others, face a future of decreased water availability combined with increased heatwave frequency and intensity. Thus, we require greater understanding of the effects of heatwaves and water use at different times during development on grapevine physiology and berry composition and wine chemistry and quality. In two consecutive years, we evaluated the impact of different pre-heat wave irrigation practices on vine physiology and berry composition across the 2019 and 2020 growing seasons in a commercial Cabernet Sauvignon vineyard in the Northern Central Valley of California (Lodi, CA). Differential irrigation treatments were applied only when a heat event took place and started one or two days before each heatwave and continued until the last day of the heat event. Three irrigation treatments were implemented:

• A control or baseline, which was exposed to deficit irrigation and held at 60% evapotranspiration (ET)
• A second treatment where the irrigation was double the baseline (2× baseline ET)
• A third treatment with triple the amount of water of the baseline (3× baseline ET)

Replicated wine lots were fermented from each treatment following a standard red wine fermentation protocol. Two trained sensory panels characterized the aroma and flavor profiles of the wines. Moreover, the wines’ volatile and phenolic profiles were analyzed and compared to the sensory. Vines could recover from physiological stress caused by heat events, but berry biochemical traits were negatively impacted. Negative effects on berry chemistry resulted from over- and underwatering during heat waves. The sensory results showed how these differences translated to the wines’ sensory properties and chemical characteristics.

Funding Support: Ray and Louise Rossi Endowed Chair Funds, NSF, E&J Gallo Winery