Soybean Seed Quality Due to Fungal Infections

Host: Joanna Coles, Warren County Extension Agent for Agriculture & Natural Resources

Guest: Dr. Carl Bradley, UK Extension Plant Pathologist

Topic: Soybean Seed Quality due to Fungal Infections

Little rainfall during August and most of September led to poor soybean pod integrity. With the rains that remnants of Hurricane Helene had dropped, along with the warm temperatures, a scenario developed that led to soybean seeds being infected and contaminated with some fungi.  

In general, Phomopsis seed decay (caused by species of a fungus known as “Diaporthe”) and purple seed stain (caused by species of a fungus known as “Cercospora”) have been the two main culprits of poor seed quality this year. Symptoms that are occurring on soybean seeds include shriveled seeds, misshapen seed, seeds that are chalky white or dark brown in color, and seeds with purple blotches or entire seeds that are discolored purple. Again, the primary reason for seeing these problems this year is the timing of the rainfall during harvest as well as the warm temperatures, which were great conditions for the fungi to grow and cause these problems.  

Although application of foliar fungicides will help protect against leaf diseases, their effect on pod and seed diseases is limited, especially when weather conditions become very favorable for fungi to infect seeds during the harvest season. In the future, the primary way to manage this problem is to harvest soybean fields as soon as possible after they become mature.  Being sure that the maturity of the soybean varieties planted match up well with your farming operation is of most importance.