Affected stems on plants with sclerotium s … Affected stems on plants with sclerotium stem rot first show a moist decay at or slightly below the soil surface where infection is initiated. Stem lesions expand up and down the stem, and all plant parts can be infected. Stem infection leads to wilting and yellowing of the foliage. Tubers are typically infected by way of stolons. The fungus quickly grows over the tuber surface and invades, resulting in a moist cheesy decay. Portions of infected plant parts and nearby soil often are covered with the white, radiating mycelium of S. rolfsii. The mycelium generates small spherical sclerotia (about 1 to 2 mm in diameter) that are white when young and brown when mature. re white when young and brown when mature.