The disease can be found in an average of more than 30 percent of soybean in central Illinois. The slower spread of this disease in Iowa may be due to Iowa growers' efforts in monitoring and preventing this disease. The Iowa Soybean Promotion Board and seed companies have devoted considerable effort in education of disease prevention since the disease was found in Iowa. Symptoms of the disease occurred after the mid-August. Initial symptoms of top dieback are yellowing and death of leaves in the upper portion of the plant canopy followed by discoloration of internodes.
Plants die prematurely when the disease is severe.
A preliminary study indicated that symptoms of this disease can be enhanced by nutrient deficiencies in soybeans. Northern stem canker occurred in higher frequency this past summer not only in Iowa but also in neighboring states. The same fungus that causes top dieback also may cause northern stem canker. Infected plants, noticeable because of leaf necrosis at the top of the plant, may be scattered or found in patches within the field. Like top dieback, this disease is seedborne and infected seeds are small and shriveled.