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.

Frogeye leaf spot lesions generally begin to appear after soybean plants begin to bloom. Leaf lesions caused by frogeye leaf spot may appear on any part of the plant but will usually be on the lower to middle part of the plant. These lesions may be on the leaves of the upper plant especially during the later part of the growing season when day length is shorter and temperatures are lower than in August.

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.

Information on these pages is from the cooperative effort of researchers throughout the North Central states. Information from this site can be copied and distributed for educational use. Please credit the source with our name and URL: NCSRP Plant Health Initiative at www.planthealth.info. Please do not use copyrighted photos without permission.