Charlotte Oliver and Michelle Moyer*
*Washington State University – IAREC, 24106 N Bunn Rd, Prosser, WA, 99350 (michelle.moyer@wsu.edu)

Fungicide use, especially sulfur, is currently an indispensable part of powdery mildew management in United States winegrape production. Sulfur has a long history of effective use for disease control and there is very low risk of Erysiphe necator resis­tance development. This makes sulfur important for fungicide resistance manage­ment and product stewardship. Understanding how applicators are using sulfur can inform extension efforts and improve use recommendations. The Fungicide Resis­tance Assessment Mitigation and Extension (FRAME) network collected winegrape fungicide records from growers in California (CA, 51 vineyards), Oregon (OR, 43 vineyards), and Washington (WA, 15 vineyards) to take an in-depth look at sulfur use between 2016 and 2020. During this period, on average, sulfur comprised 35% of the total fungicides applied in-season, with a range of 25% (WA) to 39% (OR). On an annual basis, sulfur use increased from 27% (2016) to 41% (2020) of total fungicides applied in-season. The prevalence of sulfur use and application method, alone or in a mix, was dependent on the time of season applications were made. For example, 62% of all first in-season applications were either solely sulfur (46% of total applications) or contained sulfur as a partner in a tank mix (16%). In contrast, only 8% of the last in-season sprays were either solely sulfur (2% of total applications) or contained sul­fur as a partner in a tank mix (6%). This reduced sulfur use late-season is likely due to concerns related to daytime high temperatures or residue carryover into the winery. Preliminary analyses suggest that applicators are using sulfur in ways that align with extension fungicide stewardship recommendations: using it early season as a contact product application, and generally increasing its use between 2016 and 2020 as a tank mix option for fungicide stewardship.

Funding Support: United States Department of Agriculture – National Institute for Food and Agriculture – Specialty Crop Research Initiative Award No. 2018-03375, and in part by: USDA National Institute of Food and Agriculture, Hatch project 1016563