First Detection of Frogeye Leaf Spot in Soybean Fields in North Dakota and the G143A Mutation in the Cytochrome b Gene of Cercospora sojina

Frogeye leaf spot, caused by Cercospora sojina, is an important foliar disease of soybean (Glycine max) in the United States. Application of quinone outside inhibitor (QoI) fungicides has been an important tool available to farmers to help manage this disease, but in 2010, C. sojina isolates with resistance to QoI fungicides were first discovered in Tennessee and then additional states in the years to follow. During the 2020 growing season, C. sojina isolates collected from North Dakota soybean fields were tested for QoI resistance using laboratory and molecular assays. The results of these assays showed that QoI fungicide-resistant C. sojina isolates are present in North Dakota. Similar to previous findings in other states, these QoI-resistant C. sojina isolates contain the G143A mutation. Soybean farmers in North Dakota will need to use an integrated approach of cultural practices, genetic resistance, and fungicides with multiple modes of action to manage this disease in light of QoI-resistant C. sojina isolates being present in the state.