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.

Fig 1: Lesions from frogeye leaf spot in soybean

Fig 2: Gray sporulation (conidia) on the underside of a soybean leaf

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.

References

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

spot of Soybean. Retrieved from:

https://cropprotectionnetwork.org/encyclopedia/frog

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

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

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

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

quinone outside inhibitor fungicide-resistant isolates

of Cercospora sojina, causal agent of frogeye leaf

spot of soybean, in the United States. Plant Health

Progress, 19(4), pp.295- 302.

Authors: Madeline Henrickson and Dr. Alyssa Koehler

UD Cooperative Extension

This institution is an equal opportunity provider.

In accordance with Federal law and U.S. Department of Agriculture policy, Cooperative Extension is prohibited from discriminating on the basis of race, color, national origin, sex, age, or disability.