A soilborne disease caused by the fungus Thielaviopsis basicola and usually occurs early in the season. Favorable conditions include cool conditions early in the season and it is more often found in fields with damaging levels of nematodes. Thielaviopsis root rot has been reported in Michigan and southwestern Ontario as well as Arkansas and Mississippi.
Symptoms include stunting and shortened internodes as well as yellow spots along the leaf veins. Thielaviopsis root root is also referred to as black root rot because roots are infected by the fungus causing black discoloration of the taproot and rotting of the hypocotyl. Plants infected often have shallow root systems more susceptible to moisture stress.
Discoloration of soybean taproot and hypocotyl caused by Thielaviopsis root rot. Image: S. Monfort.
Cotton and tobacco are hosts of the pathogen which overwinters on crop residues.