Plant Health Initiative

Frogeye Leaf Spot - Scouting

Frogeye leaf spot is likely to be more severe where trees provide early morning shade and longer periods of dew.

Individuals scouting for frogeye leaf spot should examine soybean plants for symptoms in at least one area for each 10 acres and should be diligent about inspecting plants in areas of a field that are shaded early in the morning because of nearby trees or buildings.

Check for frogeye leaf spot when soybean plants begin to bloom. Leaf lesions may appear on any part of the plant but will usually be on the lower to middle part of the plant. Lesions on the upper part of the plant are more common later in the growing season when day length is shorter and temperatures are lower than in August.

 

Check the lower part of the plant for lesion. Frog eye leaf spot is fairly easy to recognize. Photo credit: A. Wrather, University of Missouri.

The number of lesions on a leaf and the number of leaves with lesions may vary greatly from field to field and even within a field; this variation is most often due to small environmental differences within a field and between fields. For example, disease will likely be more severe on the west side of a north-south oriented fence row with tall trees or wooded area because the trees provide early morning shade so dew remains on the soybean leaves longer in the morning than on soybean not shaded. The extended time dew remains on the soybean leaves can enhance infection by Cercospora sojina and result in more symptoms.