Song Yan, George Zhuang, Qun Sun, and Anita Oberholster*
*Department of Viticulture and Enology, University of California at Davis, 595 Hilgard Lane, Davis, CA, 95616 (aoberholster@ucdavis.edu)

Smoke exposure can negatively affect grapes and resulting wines by absorption of smoke-related phenols released into the air during wildfires. Currently, studies inves­tigating the impact of canopy management on volatile phenol absorption have been inconclusive, with no clear benefit from pulling leaves after smoke exposure or thicker canopies to protect grape bunches during smoke events, even though it has been shown that translocation of volatile phenols between leaves and grapes is possible. The main objective of this study was to determine the interactive effect of water defi­cit and mechanical leafing on canopy structure and grape smoke exposure risk. The field experiment was conducted at a commercial Cabernet Sauvignon vineyard (clone 08) on Freedom rootstock planted in 2013 in Madera County, CA. The vine spacing is 4’ × 10’ (vine × row), with the row planted at a 45° angle on a Northeast-Southwest orientation. This experiment was a two (sustained deficit irrigation/regulated deficit irrigation) × three (leaf removal at bloom ~400 GDD/fruit set ~630 GDD/no leaf removal) factorial design with five replicated blocks. Sample analysis for both grape and wine free and total volatile phenols was conducted using liquid-liquid extraction (LLE) combined with gas chromatography-mass spectrometry (GC-MS). There were two large wildfires in 2020 in the vicinity of the experimental vineyard, the River Fire (from 16 Aug to 4 Sept) and the Creek fire (from 4 Sept to 24 Dec 2020). In 2020, there were 14 days with an AQI >150 during the growing season, compared to an average of <1 day in the previous three years. Results indicate that smoke impact was generally low, resulting in relatively small differences in the volatile phenol composi­tion of the grapes and wine. Further studies under more extreme conditions are need­ed to determine the potential impact of canopy on smoke exposure risk.

Funding Support: The Wine Group (TWG) JASTRO & SHIELDS GRADUATE RESEARCH AWARD