Frogeye leaf spot is an economically important disease in the Midwest and mid-southern soybean producing states. Last week, we began observing suspected Frogeye leaf spot in North Dakota for the first time (Sargent and Richland Counties), and believe it may be more widespread. While economic loss is not likely this season (soybeans are too mature), the pathogen overwinters in seed and residue so it is possible that Frogeye leaf spot could become an issue next year. The disease can be managed with fungicides, but the pathogen has become resistant to the FRAC 11 group of fungicides (strobilurins) in some locations in the United States (including Southern Minnesota). This group of fungicides includes some of the most commonly used in agriculture, such as Headline, Quadris, Aproach and pre-mixes of these compounds). It is very important to determine if the pathogen occurring in North Dakota is resistant to FRAC 11 fungicides before making management recommendations next growing season.

1) Determine how widespread Frogeye leaf spot is in North Dakota, and determine if the pathogen is resistant to FRAC 11 (strobilurin) fungicides. This will enable us to make management recommendations to growers in 2021.
2) Evaluate fungicide efficacy to frogeye leaf spot in two fungicide trials conducted in ND
3) Develop & deliver frogeye leaf spot information to growers in ND. Including Extension publication, video, and educational presentations.
4) Develop skills to work with frogeye leaf spot in laboratory, greenhouse and field studies.

Information will be used to help develop management recommendations for North Dakota soybean growers for 2021. Hopefully, the analysis will be completed prior to winter meeting. Recommendations will be distributed by as many means as possible, include through NDSU Extension, media and many partners in the private sector.

Updated December 1, 2020:
2020 Mid-Term Progress Report
Prepared: Sam Markell
Date: 12/01/20

Frogeye Leaf Spot was visually observed in North Dakota for the first time in Sargent County in late August 2020. By the second week of September, members of the broadleaf crop Extension project (Ph.D. student Brandt Berghuis and research specialist Bryan Hansen) had surveyed five fields each in ten North Dakota counties. Each field was surveyed by walking a W-pattern in two different field locations; the first along a shelter belt (where microclimates are most favorable for disease) and the second in an arbitrarily selected location within the field.

Frogeye leaf spot was found in the majority of fields surveyed south of a line from Traill county. Specifically, Frogeye leaf spot was found in; 5 of 5 fields scouted in LaMoure, Ransom, Richland, Sargent and Stutsman Counties; in 4 of 5 fields in Barnes, Cass and Dickey Counties; in 2 of 5 fields in Triall County; and in 0 of 5 fields in Grand Forks County. Severity levels within the fields ranged from approximately ‘trace’ to 10%.

Infected leaves were sent to the laboratory of Dr. Carl Bradley at the University of Kentucky for determination of sensitivity to QoI fungicides (aka, FRAC 11/strobilurins, such as Aproach, Headline and Quadris). Post-doctoral scholar Danilo Lima Das Neves was able to recover approximately 200 pathogen isolates. To date, 45 of those isolates are showing QoI-resistance, based on a discriminatory dose assay (microbiological technique with fungicide-treated agar on petri plates). Molecular confirmation is underway. So far, putative QoI resistance has been found in Barnes, Dickey, LaMoure, Ransom, Richland, Sargent, Stutsman, and Traill counties. Essentially, we must assume that it is widespread throughout the state.

In the next couple months, we anticipate confirmation of QoI resistance, development of Extension materials and management materials on Frogeye leaf spot. Information will be distributed at winter meetings (virtual and/or in-person) and through partners, media and Extension sources. We thank the North Dakota Soybean Council for their support.

This will enable us to make management recommendations to growers in 2021.