Plant Pathology: Extension & Outreach: Plant Disease Library

Rhizoctonia

Important diseases:  Brown patch of turf, Belly rot of squash, Damping off, Web blight

Rhizoctonia is the most important pathogen worldwide. It causes a variety of different disease including damping-off. Seedling stem canker ("soreshin"), tuber and root rots, leaf blight and rots on vegetables and fruit.

Symptoms vary, but usually affected tissue has brown, round to irregularly shaped spots. Spots may be sunken and "dry" in appearance. Infection is often at the soil line or just below. Under warm, wet conditions, Rhizoctonia can cause an aerial or web blight, infecting the interior of densely-growing plants including azaleas and hollies.

Rhizoctonia does not produce spores. It exists as mycelium and sclerotia (hardened, overwintering masses of mycelium). The key to identifying Rhizoctonia are three characteristics of its septate (with cross walls) hyphae: 1) branches at 90 degree angles, 2) constrictions at the base of the hyphal branching, and 3) clear to tan to light brown color.