Plant Health Initiative

Management of Frogeye Leaf Spot

A longer rotation is effective in reducing the amount of the frogeye leaf spot pathogen in soybean fields. Photo credit: University of Nebraska, Crop Watch

Frogeye leaf spot is best managed by planting resistant soybean varieties. Several high-yielding maturity group 4 and 5 varieties have resistance to frogeye leaf spot and are available for planting in the southern U.S.; however few are adapted for planting in the northern U.S.

There are several types, or ‘races’, of the pathogen, Cercospora sojina, that causes frogeye leaf spot in the U.S., and soybean varieties that have the gene for frogeye leaf spot resistance labeled Rcs3 are resistant to all types. This gene for frogeye leaf spot resistance was first available in a maturity group 6 soybean called ‘Davis’. Many maturity group 4-6 soybean varieties have been developed with this gene, and they are resistant to all races of this pathogen. Unfortunately, few maturity group 1-3 varieties have this gene because of the difficulties breeders have had in crossing early- maturing varieties, maturity group 1-3, with late maturing varieties, maturity group 5-7.

Crop rotation may help reduce the severity of frogeye leaf spot, but long rotations may be required. The fungal pathogen will survive in soybean residue until the residue completely decomposes, and this complete decomposition may take more than one year. Therefore, a soybean-corn-soybean rotation may not be useful for frogeye leaf spot management, but a soybean-corn-corn-soybean rotation will be more effective.

Tillage may or may not affect frogeye leaf spot. Because the fungus survives in residue, it is logical to speculate that tilling infested residue will reduce the pathogen population. However, although we know that some soybean diseases are more severe in reduced or no-till fields, some are less severe, and some not affected, no one has yet shown that tillage affects frogeye leaf spot. Experiments are currently underway in the North Central region to determine the effect of tillage on the disease. They will be completed in 2 to 3 years.

Frogeye leaf spot may be effectively managed by application of the strobilurin class of fungicides, Quadris or Headline, to soybean foliage from the R3 to R5 stages of soybean growth, but this method of frogeye leaf spot management is expensive. Fortunately, an application of one of the products in this class will help manage other soybean diseases such as brown spot, Cercospora leaf blight, anthracnose, and pod and stem blight.

 

Plant high-quality seeds relatively free of the pathogen.

 

Contributors

Dr. Allen Wrather, University of Missouri
Dr. Jason Bond, Southern Illinois University
Dr. Kiersten Wise, Purdue University
Dr. Alemu Mengistu, USDA-ARS
Dr. Carl Bradley, University of Illinois
Dr. Alison Robertson, Iowa State University