Foliar fungicide use in agronomic field crops has increased greatly over the last decade. This increased use of foliar fungicides has resulted in an increased risk of development of fungicide resistant strains of important plant pathogens.

With support from the United Soybean Board, the Kentucky Small Grain Growers’ Association, and industry partners, Dr. Bradley’s program evaluates for fungicide-resistant pathogens of soybean and wheat in Kentucky and across the U.S. Working with colleagues from North Dakota and Wisconsin, Dr. Bradley’s research program identified strains of the frogeye leaf spot pathogen of soybean (known as the fungus Cercospora sojina) in those states for the first time ever from soybean leaf samples collected during the 2020 growing season. This brought the total states with fungicide-resistant strains of Cercospora sojina to 21 states, showing that this issue continues to be a developing problem across the entire soybean production region in the U.S.  Locally, Dr. Bradley’s research program has identified these fungicide-resistant strains of Cercospora sojina across most of western Kentucky and in some fields in northern and central Kentucky.

In addition to monitoring for fungicide-resistant strains of soybean pathogens, Dr. Bradley’s research program also has identified fungicide-resistant strains of the pathogens that cause leaf blotch of wheat (known as the fungi Parastagonospora nodorum and Zymoseptoria tritici). In this project funded by the Kentucky Small Grain Growers’ Association, several wheat fields sampled in western Kentucky have strains of these fungi that are resistant to the strobilurin class of fungicides, which is one of the most important classes of fungicides used on field crops in the U.S.

Monitoring and identifying fungicide-resistant strains of important plant pathogens of agronomic field crops helps alert farmers about the risk of fungicide resistance in their area, and helps them make important management decisions that will result in adequate disease management and the best fungicide resistance management practices.