Plant Health Initiative

Symptoms of Frogeye Leaf Spot

Leaf lesions are first noticed after plants begin to bloom. These lesions are irregularly circular, with a light-brown center, and a dark-brown to dark-purple border. They are most often the size of the end of a pencil eraser, about ¼ inch in diameter. The spots may be surrounded by a narrow yellow margin. Some leaves may have few lesions, and some may have many, up to 30% of the leaf surface covered with lesions. The lesions caused by the frogeye leaf spot pathogen are easily distinguishable from those caused by most other diseases.

Lesions caused by the frogeye leaf spot pathogen are easily distinguishable from those caused by most other diseases. Photo credit: A. Wrather, University of Missour.

Stem lesions are less common and generally appear late in the season. Lesions on pods are circular to elongate and slightly sunken, with a reddish brown color. As these pod lesions age, they become brown to light gray with narrow dark-brown borders. The pathogen can penetrate through the pod wall and infect the developing seeds.

Symptoms on seeds appear as conspicuous light to dark gray or brown areas that can range from specks to large blotches covering the entire seed coat, and this seed coat may crack or flake.