Crop & Pest Report

Accessibility


| Share

Soybean Frogeye Leaf Spot Update (09/24/20)

During the week of September 7th, we conducted a survey to determine the prevalence of Frogeye Leaf Spot in North Dakota soybeans.

During the week of September 7th, we conducted a survey to determine the prevalence of Frogeye Leaf Spot in North Dakota soybeans. The disease was observed in the state for the first time in late August in Richland and Sargent counites, and it was very important to determine how widespread it was before the growing season ended. We thank the North Dakota Soybean Council for supporting the effort.

We visited the eight Southeastern counties (Richland, Sargent, Ransom, Dickey, LaMoure, Stutsman, Barnes and Cass) plus Traill and Grand Forks. In each field, we surveyed two locations for Frogeye, and assessed five clusters of plants by walking a W-pattern at each location. The first was near a shelterbelt (whenever possible) which provides a more favorable environment for infection (longer dews) and the second was randomly selected within the field. We estimated prevalence and severity by visually assessing signs and symptoms, which included small circular gray lesions with a reddish-purple margin on the upper side of the leaf, and gray fungal growth on the underside of the leaf (Figures 1 and 2).

We observed Frogeye in nearly all the fields we visited in Southeastern North Dakota (Figure 3). Disease severity was low in the majority fields and yield loss to the disease is not expected. Only trace levels of Frogeye were observed in Trail County and in just two fields, and Frogeye was not observed in any field surveyed in Grand Forks, suggesting a Northern limit of occurrence. Due to the freeze on September 9th we did not survey west of the Stutsman/LaMoure/Dickey line.

It is possible that the pathogen causing Frogeye (Cercospora sojina) will overwinter in North Dakota. However, it is somewhat unclear if the disease will be a concern next summer.

ppth.soybean frogeye.1 2

.Disease development next year will be heavily dependent on a favorable environment, which include high summer temperatures, high humidity and frequent rains. More information on Frogeye will be developed this winter.

ppth.iowa grower

We thank the North Dakota Soybean Council for supporting the effort, and thank the agricultural media for helping us get the word out quickly about Frogeye leaf spot.

 

Sam Markell

Extension Plant Pathologist, Broad-leaf Crops

 

Brandt Berghuis

Graduate Research Assistant and Ph.D. Student

NDSU Plant Pathology

 

Bryan Hansen

Research Specialist

NDSU Plant Pathology

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

USDA logo

Creative Commons License
Feel free to use and share this content, but please do so under the conditions of our Creative Commons license and our Rules for Use. Thanks.