Frogeye Leaf Spot Spreads Across Mississippi

Frogeye Leaf Spot has been a major concern for Mississippi farmers for the last several years. In 2014, a study funded by the Mississippi Soybean Promotion Board (MSPB) sampled over 630 soybean leaves from 73 counties and found that frogeye leaf spot strains resistant to the strobilurin class of fungicides was present in at least one field in all 73 counties.

“The 2014 sampling of frogeye leaf spot has provided us with the most comprehensive disease distribution in Mississippi to date,” says Maria Tomaso-Peterson, Ph.D., Mississippi State University plant pathologist. “Documented distribution of frogeye leaf spot may provide informed decision-making in terms of selecting a resistant soybean variety to reduce disease outbreaks as well as monitoring the spread of the pathogen.”

Although fungicide resistance is not as widespread as herbicide-resistant weeds, now is the time for farmers to get ready for it. MSPB member and United Soybean Board Director David Wansley, who farms in Vicksburg, says he’s taking preventative steps now.

“Foliar soybean diseases, such as frogeye leaf spot, can cause significant yield loss,” says Wansley. “Since we are already dealing with the expense of resistant weeds, we sure don’t need a resistance in the soybean-pathogen department. It is important that farmers use best-management practices to keep resistance in check.”

If farmers see frogeye leaf spot on their farm year after year, then management of that disease should become more of a priority. Integrating different practices for disease management will result in the highest level of disease control. Those practices include:

Choosing a resistant variety. Tomaso-Peterson says frogeye-leaf-spot-resistant soybean varieties should be considered as a tool in managing fungicide resistance, along with other best management practices.

Fungicide diversity. If the farmer decides to apply a foliar fungicide, it is important to use a product that contains multiple active ingredients (or tank-mix products) from different chemistry classes.

Crop rotation. The first case of fungicide-resistant frogeye leaf spot documented was from a field that had been in continuous-soybean production for several years, according to Tomaso-Peterson.

Online resources can help farmers who are looking for more information about the problem and how to prevent it. The MPSB website and Mississippi Crop Situation blog contain basic information about fungicide resistance.