Rhizoctonia fungi are natural soil inhabitants that colonize and live on dead organic matter. Under the right environmental conditions, they are often able to attack living plants, including alfalfa. Under warm, wet conditions, Rhizoctonia fungi can cause just about every conceivable type of alfalfa disease. Important examples are listed below. Another soilborne fungus, Rhizoctonia crocorum , causes decayed roots to appear cinnamon brown to violet in color.
Infected tissues appear dark brown to black.
Foliage of infected stems wilts and turns yellow, sometimes with reddening. During morning dews, cobwebby fungal strands may be evident on infected tissues. Rhizoctonia diseases of alfalfa are very common in Kentucky, as our warm, humid climate is very favorable for these fungi. Poor drainage and excessive growth can also favor these diseases. Another factor that favors Rhizoctonia diseases is undecomposed organic matter, particularly if it is high in nitrogen.