Southern blight of tomato caused by the soil-borne fungus Sclerotium rolfsii. Disease development is favored by a combination of hot weather and high soil moisture. Stem cankers at the base of the plant caused by Sclerotiu rolfsii. The white fungal growth associated with the cankers is a good diagnostic characteristic of this disease.

Plants with southern blight seemingly wilt overnight. This fungus causes a brown-colored canker on the stem near the soil line. The canker develops rapidly and girdles the stem, causing the entire plant to wilt. Note the presence of sclerotia (survival structures) at the base of the plant, which enable the fungus to survive in soil and plant debris for many years. Sclerotium rolfsii also attacks tomato fruit in contact with the ground. Note the abundance of sclerotia, which are initially white but turn brown with age.