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

Development of fungicide resistance is often attributed to practices such as product over-use, product misuse, and poor timing. While applicators assume their practic- es adhere to recommendations for fungicide resistance mitigation, validating those assumptions can be difficult. One approach for validation is broad-scale evaluation and analysis of regional historical fungicide records across multiple farming entities. The Fungicide Resistance Assessment Mitigation and Extension network has been collecting fungicide records from informed and consenting growers in Michigan (MI), Oregon (OR), and Washington (WA) to take a national look at spray practices and identify potential issues contributing to the selection of fungicide resistance. These records span from 2015 to 2019. The mean of yearly applications was seven; by state, the mean ranged from six (WA) to eight (OR). The mean application interval was 14 days; by state, the mean ranged from 13 (OR) to 16 (MI). Using a subset of data from OR and WA with continuous records from 2016 to 2019, we saw a reduction in FRAC3 use (-6% in OR and -9% in WA). There was also a reduction in FRAC 9 (-5%) and FRAC 11 (-4%) fungicide use in WA. We saw an increase in FRAC 7 (SDHI) fungicide use (+1% in OR, +5% in WA), FRAC 50 fungicide use (+4% in OR, +6% in WA), FRAC U06 fungicide use (+1% in OR, +7% in WA), and FRAC M02 fungicide use (+8% in OR,
+12% in WA). This shift in product usage is likely related to increased understanding of known resistance issues in FRAC 3 and 11 fungicides. However, the product shift is also placing resistance development pressure on products such as those in the FRAC 50 and U06 classifications, which have seen resistance development due to over-use in Europe.

Funding Support: United States Department of Agriculture—National Institute for Food and Agriculture—Specialty Crop Research Initiative Award No. 2018-03375