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.

Sunflower rust, caused by Puccinia helianthi, is an economically and globally important disease of sunflower. Two types of sunflowers are produced in the US Northern Great Plains; the oilseed type and the confection type. Although approximately 80% of the acreage in this region is planted as the oilseed type sunflower, fungicide efficacy and timing studies have been conducted primarily on the more rust-susceptible confection type. A total of ten sunflower rust efficacy field experiments were conducted on oilseed type and confectionary type hybrid trials from 2016-2018. Eleven fungicides from three FRAC groups were evaluated for efficacy and protection of yield. Severity differences among fungicide treatments were identified in both confection and oilseed type sunflower trials. A combined analysis of all confection field trials (five) indicated that rust severity was lower in all fungicide treatments as compared to the non-treated control. Despite rust severity levels below the fungicide action threshold for confection sunflower, seven of the eleven fungicide treatments had yield higher than the non-treated control. In oilseed trials, rust severity was lower in all fungicide treatments as compared to the non-treated control, similar to the findings of the confection type. Rust severity was too low to detect yield differences in oilseed trials. Additional work is needed to elucidate yield-loss potential on oilseed type sunflower and refine the fungicide action threshold on confection type sunflower.