Frogeye Leaf Spot


Frogeye leaf spot, caused by the fungus Cercospora sojina, has become a significant concern for soybean growers globally.

Frogeye leaf spot can profoundly affect soybean crops in several ways:

While the disease primarily targets leaves, it can also inflict lesions on stems and pods. This can result in defoliation, diminished photosynthetic capacity, and premature plant death. In pods, the disease can degrade seed quality and trigger seed decay.

Yield losses of up to 30% have been reported in severe cases.

(Image Credit: Trey Price, LSU AgCenter,

How to Manage Frogeye Leaf Spot in Soybeans close up

How to Identify Frogeye Leaf Spot

Prompt identification of Frogeye leaf spot is crucial for its effective management and control.

Frogeye leaf spot derives its name from its distinctive symptoms. On soybean leaves, it triggers circular to angular spots that start small and dark. As the disease evolves, these spots expand to about ¼ inch in diameter and develop a gray to brown center with a reddish-purple margin, mimicking a “frogeye” appearance.

A severe infection can cause these spots to merge, leading to large, dead areas on the leaves. The disease can also trigger elongated, dark lesions on stems and pods.

Beyond visual symptoms, laboratory testing can confirm the presence of Cercospora sojina. It's vital to distinguish it from other diseases like Target Spot and Brown Spot, which can exhibit similar symptoms.

Geographic Impact of Frogeye Leaf Spot

The disease thrives in warm, humid environments, making it a common issue in the southern United States and other similar climates. However, it has been detected in nearly all soybean-growing regions worldwide.

(Image Credit: Carl Bradley, University of Kentucky,

Carl Bradley, University of Kentucky,

Timing of Frogeye Leaf Spot

Frogeye leaf spot typically manifests during the reproductive stages of the soybean growing season, although conducive conditions can trigger an earlier onset.

If infection sets in early in the season and conditions favor disease development, Frogeye leaf spot can cause substantial yield losses.

How to Manage Frogeye Leaf Spot in Soybeans

For managing Frogeye leaf spot, consider Thiophanate-methyl 4.50 Value Pick during soybean growth stage R3. While the QoI fungicides — GCS Azoxy — can help reduce disease, there are reports of QoI-resistant populations of the fungus that causes Frogeye leaf spot.


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This content was generated with the assistance of Norm℠, FBN’s artificial intelligence (AI) Ag Advisor, based on a dataset of information containing general industry best practices and research. The AI model did not use specific external sources to generate this content. Our process involves using AI to aid human subject matter experts with the initial drafting and/or refinement of content.

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