Impact
Rhizoctonia canker and black scurf are caused by the soilborne fungus Rhizoctonia solani. The fungus survives in soil as mycelium associated with decomposing plant residues. In addition, the sclerotia can survive on infected tubers and can persist free in soils for extended periods. Rhizoctonia is sporadic throughout the San Luis Valley depending on environmental conditions.

Descriptions and Symptoms
	Bacteria are carried on seed tubers, mainly in the lenticels, in a dormant state. When environmental conditions are favorable, disease expression may occur.
	High soil temperatures and bruising of seed tubers, or cool, wet and poorly aerated soils at planting, favor seed piece decay and pre-emergence blackleg. Cool, wet soils at planting, followed by high temperatures after emergence, favor post-emergence blackleg. Fusarium seed piece decay may predispose developing plants to infection by the soft rot Erwinias, resulting in increased soft rot of seed pieces and early-season blackleg.
	In severe cases, entire seed pieces and developing sprouts decay prior to emergence, resulting in uneven stands.
	In post-emergence blackleg, the basal stem area of diseased plants typically exhibit an inky black to light brown decay.
Integrated Management
	Conduct a thorough sanitation program throughout the entire farming operation.
	No resistant cultivars are available. However, cultivars vary in susceptibility to the disease.
	No pesticide control is available.
	Plant high quality, tissue-culture derived, certified seed to minimize seedborne contamination.
	Plant undamaged, whole seed tubers that are less susceptible to bacterial seed piece decay. When cut seed is used, thoroughly clean all seed-cutting and handling equipment between seed lots to minimize the spread of bacteria. Warm seed tubers to about 45 to 55 degrees F before cutting. Wound healing and suberization are critical for prevention of infections by soft rot Erwinias.
	Plant seed pieces in adequate soil moisture when termperatures are at least 50 degrees F at a 6-inch depth.

This material is based on work supported by the San Luis Valley Water Quality Demonstration Project Best Management Practices Advisory Committee, Colorado State University Cooperative Extension, Farm Service Agency, Natural Resources Conservation Service, and the U.S. Department of Agriculture under authorization as 1991 U.S. Department of Agriculture Water Quality Demonstration Project.