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Ohio State University Extension


Ask the Expert – Managing Frogeye Leaf Spot with Dr. Carl Bradley

Dr. Carl Bradley

University of Kentucky Extension Specialist Dr. Carl Bradley recently sat down with us to answer our questions on frogeye leaf spot of soybean. Dr. Bradley is a featured speaker at this year’s Conservation Tillage Conference at Ohio Northern University in Ada, Ohio on March 14-15.

Q:  What is frogeye leaf spot?
A:  Frogeye leaf spot is a foliar disease of soybean that is caused by a fungus called Cercospora sojina. It is the most damaging foliar disease of soybean in the U.S. and is most severe when the growing season is warm and humid with plenty of rainfall.

Q:  What are the management strategies for frogeye leaf spot?
A:  Integrating different management practices will provide the greatest control of frogeye leaf spot. The primary management strategies are done through planting soybean varieties with a high-level of resistance to frogeye leaf spot, rotating to non-host crops (such as corn), and applying an effective foliar fungicide during the reproductive stages of soybean development.

Q:  How common is fungicide-resistant frogeye leaf spot?
A:  Since 2010, fungicide-resistant strains of the frogeye leaf spot fungus have been observed in the U.S. These strains are highly-resistant to QoI fungicides (sometimes called “strobilurin” fungicides), and generally are present anywhere in the U.S. where frogeye leaf spot occurs.

Q:  Why should I worry about fungicide resistance?
A:  When a fungal plant pathogen (like the frogeye leaf spot pathogen, Cercospora sojina) becomes resistant to a certain group of fungicides, that group of fungicides will no longer be effective in managing the disease caused by that pathogen. Currently there are only a few different groups of fungicides that are registered for use as a foliar fungicide on soybean. When we lose one of these groups due to fungicide resistance, that leaves fewer effective fungicides available. Overall, this makes management of important diseases much more difficult.

To learn more about managing frogeye leaf spot and amidst widespread fungicide resistance, attend Dr. Carl Bradley’s presentation at the 2023 Conservation Tillage Conference on Tuesday, March 14 at 10:00 a.m. in the Agronomic Crop Management Session. Register and access the full conference schedule at

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.