Plant Pathology: Extension: Plant Disease Library

Sclerotium

Important diseases:   Southern Blight, Southern stem rot of Peanut

Sclerotium infects almost all plants except field crops such as corn, sorghum, wheat and oats.



Fruits touching the ground, vegetables with fleshy roots (carrots, beets, etc.), bulbs and rhizomes are the most susceptible to Sclerotium infection. Infected plants wilt and die. Low growing ornamentals are particularly susceptible such as Ajuga where the whole plant may turn black and die quickly. Woody ornamentals like Aucuba will rot at the crown and then die back or topple over. The first sign of infection is white tufts of mycelium (fungal thread-like material) at the base of plants that may spread over the ground in wet weather.


Sclerotium lacks fruiting structures and spores. It produces profuse white hyphae (thread-like material) on the infected plant tissues that radiates across the tissue in a fan-like pattern. The white hyphae is often diagnostic of the fungus. Microscopic examination of hyphae shows "bridge-like" structures (clamp connections) above the hyphae cross walls.


Another diagnostic feature is the production of numerous small yellow, tan, brown to black, hard sclerotia (survival structures) that resemble mustard seeds and are formed on the surface of infected tissue.