Rhizoctonia seedling blight and root rot of soybean
Rhizoctonia seedling blight and root rot is caused by the fungus Rhizoctonia solani. Pre- and postemergence damping off can occur. Infected seedlings have reddish-brown lesions on the hypocotyls at the soil line. These lesions are sunken and remain firm and dry. The root rot phase may persist into late vegetative to early reproductive growth stages. Symptoms may disappear if infected plants grow out of the root rot problems, although plants may remain stunted. Hypocotyl lesions from Rhizoctonia infection. Image: D. Mueller
Damping off caused by Rhizoctonia seedling blight and root rot. Image: M. Chilvers
The fungus survives on plant residue or in soils as sclerotia. Infection may occur soon after seed is planted. Cool, wet springs followed by hot, dry conditions are conducive to disease. Disease is more severe on light and sandy soils, and can be more common on the slopes of fields. Unfortunately, many strains of Rhizoctonia can infect corn, alfalfa, dry bean, and some cereal crops, negating the effectiveness of crop rotation.
Eliminating stress factors, such as use of herbicides that cause injury to soybean roots, can help reduce root rot problems. Fungicide seed treatments are effective against Rhizoctonia.