Fungicide Use Patterns in Select United States Wine Grape Production Regions.

Wine grape production (Vitis sp.) in the United States requires fungicide inputs for disease control. Currently, there is limited data available on vineyard fungicide use patterns. This information is important in developing tailored recommendations for disease management and fungicide stewardship. In this paper, we summarize the wine grape vineyard fungicide use patterns from four major regions, Napa and Sonoma Valleys (California), Willamette Valley (Oregon), Columbia Valley (Washington), and several smaller regions east of the Mississippi River in years 2009-2020. We learned that the average in-season total fungicide applications ranged regionally from 5.6 to 8. The most commonly applied FRAC codes in spray programs were FRAC 3, 13, and M02 across all regions, with some variation to the top four groups in each region. Most applications were made on 14-day intervals; however, shorter intervals (7-day) were favored early season, and longer intervals (21-day) were favored late season. Tank-mixing multiple active ingredients was common east of the Mississippi River during all stages of grape development; this action was typically favored during the bloom period in other regions. In a subset of records that participated in FRAC 11 fungicide resistance testing, the average number of FRAC 11 applications after testing was reduced to either no applications or one application in Napa and Sonoma Valleys. This survey provides regionally specific data related to fungicide stewardship practices that could be a focus for future stewardship messaging and fungicide resistance selection training: total product use (selection events), spray intervals (selection pressure), and tank mixing (selection management).