Treating Frogeye Leaf Spot
Posted August 2019
From article posted August 19 by Tamra Jackson-Ziems, Extension Plant Pathologist
Northeast Nebraska has reported moderate to severe frogeye leaf spot on soybean. This may also be in other parts of Nebraska on vulnerable soybean types. Before choosing a treatment option, scouting is advised to know the occurance and severity of the disease.
QoI, also called strobilurin fungicides, are proven to work best to control frogeye leaf spot. Pathogen resistance has occurred to this class of fungicides and has been widely reported in other states as well as South Dakota and Iowa counties.
To protect your fields from frogeye leaf spot, look for a fungicide with two or more active ingredients originating from a variety of fungicide classes. In the case of the disease occurring after a fungicide is applied, you can have a sample tested for resistance. Contact by email at tjackson3@unl.edu or via Twitter at @tjcksn. For the sample, put affected leaves in one gallon food storage bag and refrigerate it. Then contact Jackson-Ziems for testing or send to the UNL Plant and Pest Diagnostic Clinic in Lincoln. For more information on testing, visit the UNL Plant and Pest Diagnostic Clinic website.
The most common occurance of frogeye leaf spot is after flowering. However, it can happen at any time during soybean development. You are likely to spot it in the upper canopy of the crop. In the beginning, dark spots appear on the leaves of the plant. They start small and grow to approximately ΒΌ inch wide. The middle of the spots change in color to gray or brown with a reddish-purple surrounding it. These spots will appear in patterns.