The disease was initially reported in Ohio 20 years ago and was first noticed in Iowa in 1997. Foliar symptoms of this disease occur during the reproductive stage of soybean plants in August, but the fungi associated with the disease can cause damage during the seedling stage. In the 1998 growing season, we received reports and questions from producers on the occurrence of black lesions on cotyledons. In this article we provide information on seedling disease caused by the same fungi that caused these lesions. These fungi produce abundant spores that are dispersed by wind and rain onto soybean plants.
Infected seedlings are noticeable by the presence of dark lesions on the cotyledons.
In some fields, more than 90 percent of the seedlings can be found with infected cotyledons. If the infection occurs early under favorable weather conditions, especially with high precipitation, the potential damage is seedling damping-off. Lesions on a cotyledon. In most plants that we observed, the infected cotyledons dropped without subsequent seedling damping-off. The fungi, however, may remain in the plants without causing symptoms until plants are stressed.