Field Guide     Crop Diseases     Frogeye Leaf Spot

Frogeye Leaf Spot


>Frogeye Leaf Spot

Family: Mycosphaerellaceae

>Frogeye Leaf Spot >Frogeye Leaf Spot

About Frogeye Leaf Spot

Life Cycle

Frogeye Leaf Spot is a fungal disease caused by the fungus Cercospora sojina. This pathogen is able to overwinter in soybean plant debris and seeds, carrying the disease over from season to season. Plants are initially infected by the spores on plant debris, which are spread further through splashing water and/or wind. Additionally, plants can become infected through lesions on plant tissue. Disease symptoms are typically visible shortly after plants begin to bloom. When the season is over, spores will overwinter in plants materials and seeds, repeating the cycle for next season.

Frogeye Leaf Spot Identification and Habitat


Initially, the most identifiable symptom of frogeye leaf spot is the small, angular, water-soaked spots on the leaves of the plant. These spots appear as dark brown, with light brown centers. As the spots age, the lesions may coalesce to cover a large amount of surface area of the leaf. In severe cases, leaves can wilt and fall prematurely. Stem lesions can also be affected, showing reddish brown lesions that are slightly narrower than those on leaves. On pods, lesions are similar to those on the leaves. If the fungus breaches the pod wall, seeds can be discolored and cracked.


In terms of weather conditions, warm and humid weather favor the development of frogeye leaf spot. In this weather, the disease causes the most severe damage (e.g. defoliation). Intermittent rains help to spread the disease from plant to plant through splashing water. Young leaves are more susceptible to infection from splashing water transmission. Infection is most common to occur after plants begin to flower. Higher leaves on the plant are more likely to be affected by the pathogen, but all leaves are vulnerable.

Frogeye Leaf Spot Management and Control Methods

Cultural Control

Avoiding frogeye leaf spot is the most effective way to deal with the disease. Plant disease-free seeds to avoid introducing the pathogen to new locations. Tillage of crops can limit the amount of plant debris on soil, which greatly reduces the chances of the infection being spread from plant to plant. Planting resistant varieties of soybean is a great way limiting further infection of crops and reducing spread of the pathogen. Another way to break the disease’s cycle is to rotate crops. This is a simple and common way of reducing chance of infection for the next growing season. Remove any diseased plants and/or plant materials from the soil to stop spores from dispersing easily.

Chemical Control

The risk of infection can be reduced through the use of fungicides. Seed treatment is a good idea, especially if nearby crops have been affected by frogeye leaf spots in previous seasons. As the plants begin to flower, fungicide spray can be applied to reduce disease severity. Applications in the beginning pod stage (R3) are considered to be the most effective deterrents. Before using fungicides, read labels for safety procedures and application guides.