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Frogeye Leaf Spot

October 2025 |听Written by:听Madeline Henrickson and Dr. Alyssa K. Betts

Pest Background

• Caused by the fungus Cercospora sojina.
• Occurrence and severity of this disease varies across the region.
• Resistance to Group 11 (QoI) fungicides has been widely documented.

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Identification

• Symptoms are not usually visible until after flowering and are first seen in the upper canopy.
• Leaf symptoms include small, irregular to circular lesions with red to brown borders (Fig 1).
• The center of older lesions may become gray to light brown and sporulation may be visible on the underside of the leaf (Fig 2).
• Lesions can coalesce leading to premature defoliation.

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Management

• This fungus survives in soybean residue, infected seed, and can spread by airborne spores.
• Varieties with resistance are available.
• Rotation to non-host crops such as corn or small grains can reduce pathogen survival.
• Foliar fungicides can be applied at the R3 to R5 growth stages following the label.
• QoI fungicide resistance has been documented in the region. Using products with two or more active ingredients from multiple fungicide FRAC classes will be more likely to effectively control disease.

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References

听听听听Crop Protection Network (2022, Jan 25). Frogeye leaf

听听听听spot of Soybean. Retrieved from:

听听听听https://cropprotectionnetwork.org/encyclopedia/frog

听听听听eye-leaf-spot-of-soybean Zhang, G., Allen, T.W., Bond,

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听听听听J.P., Fakhoury, A.M., Dorrance, A.E., Weber, L., Faske,

听听听听T.R., Giesler, L.J., Hershman, D.E., Kennedy, B.S. and

听听听听Neves, D.L., 2018. Widespread occurrence of

听听听听quinone outside inhibitor fungicide-resistant isolates

听听听听of Cercospora sojina, causal agent of frogeye leaf

听听听听spot of soybean, in the United States. Plant Health

听听听听Progress, 19(4), pp.295- 302.

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Authors:听Madeline Henrickson and Dr. Alyssa Betts

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