Resistance to Quinone Outside Inhibitor Fungicides Conferred by the G143A Mutation in Cercospora sojina (Causal Agent of Frogeye Leaf Spot) Isolates from Michigan, Minnesota, and Nebraska Soybean Fields

Frogeye leaf spot, caused by Cercospora sojina, is an eco- nomically important foliar disease of soybean (Glycine max) in the United States. The estimated average annual soybean yield losses caused by frogeye leaf spot in the United States and Ontario, Canada, from 2010 to 2014 ranged from 101,432 to 493,880 metric tons (Allen et al. 2017). Historically, frogeye leaf spot has been more prevalent in the southern United States, but the incidence and estimated yield losses caused by frogeye leaf spot in the northern United States have increased recently. For example, total estimated yield loss for northern states between 2010 and 2014 was 689,782 metric tons, but it increased to an estimated 2,172,059 metric tons between 2015 and 2019 (Crop Protection Network, Soybean Disease Loss Calculator, https://cropprotectionnetwork.org/). From a perspective of relative rank among other diseases, frogeye leaf spot was never in the “top 10” diseases for estimated losses in northern states from 2010 to 2014 (Allen et al. 2017), but it was in the top 10 for northern states three times from 2015 to 2019, with the greatest estimated losses in these states occurring in 2018 (1,283,750 metric tons) (https://cropprotectionnetwork.org/).