Field Facts: Frogeye Leaf Spot
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Frogeye leaf spot is a perennial threat in many states, especially in the South and Midsouth. However, this disease can appear anywhere and at any time that weather conditions are right. Frogeye leafspot is known to account for yield losses of up to 35%, so customers will want to watch out for this disease in soybean fields — especially during periods of warm, wet weather.
- Common name: Frogeye leaf spot
- Scientific name: Cercospora sojina Hara
- Symptoms: The most common initial signs are small, yellow spots on leaves. The spots enlarge to a diameter of about ¼ inch. Lesion centers become gray to brown and have reddish purple margins and are often mistaken for herbicide drift or other leaf diseases.
- Conditions for development: Temperatures in the high 70s and 80s F, frequent rain and high humidity
Fast facts
- Frogeye leaf spot is caused by the fungus Cercospora sojina. Unlike other soybean diseases, it produces disease on younger upper foliage, rather than older foliage at the base of plants. Diseased plants tend to have a layered appearance because infection is more severe on young leaves.
- Field infection risk is increased by conservation tillage, continuous soybean production and overreliance on a single fungicide mode of action.
- Frogeye leaf spot that is resistant to quinone outside inhibitor (QoI) fungicides has been confirmed in Illinois, Minnesota, Missouri and most southern soybean-growing states.
- The first signs of frogeye leaf spot usually occur after flowering but can occur at any stage. Check tops and undersides of leaves for tan-brown elliptical lesions with brown to purple borders.
- Spores are spread by wind and rain. Under humid conditions, inspection with a hand lens may reveal long, silver, spore-bearing hyphae extending from black dots on the underside of leaves.
Control tips
- Like many other diseases, the best way to control frogeye leaf spot is to keep it from developing in the first place. A timely fungicide application can help prevent frogeye leafspot.
- Aproach® Prima fungicide offers two powerful modes of action that provide preventive and curative action against the disease.
- Begin fungicide applications prior to disease development and make a second application on a 7-to-14-day interval, depending on the targeted disease. Use the higher specified rate and shorter interval when disease pressure is high.
- Scout fields often, as lesions don’t start to appear on leaves until about two weeks after infection sets in.
- Encourage customers to plant resistant soybean varieties, rotate crops and till fields to promote decomposition of infected residue.
- The Corn & Soybean Disease ID Guide from Corteva Agriscience provides further information about frogeye leaf spot and other common soybean diseases.
Aproach® Prima is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.