Impact
Pink rot is caused by the soilborne fungus Phytophthora erythroseptica. Pythium leak is caused by several species of a closely related soilborne fungus Pythium. Pink rot and Pythium leak sometimes are collectively called water rot or leak. These diseases usually are of economic concern when tubers are exposed to saturated soils for several days in succession during maturation and soil temperatures are above 70 degrees F. Leak and pink rot in susceptible cultivars are most severe in the San Luis Valley when warm, wet conditions prevail late in the growing season.

Pink rot (Robert Davidson).		Pythium leak.

Descriptions and Symptoms
Pink Rot
	The pathogen can enter tubers through diseased stolons. Tuber infections also occur at eyes and lenticels.
	The decay spreads through infected tubers quickly. The advancing margin of the rot is sharply defined by a dark line, which may be visible through the skin.
	Decaying tubers remain intact, are spongy and have a distinct odor. If squeezed, a clear liquid exudes.
	The internal tissue of a cut tuber turns salmon pick after exposure to the air for 15 to 20 minutes then turns brownish black.
Pythium Leak
	Tuber wounds during harvest and handling are the main infection sites for Pythium. The disease begins as a discolored, water-soaked area.
	As with pink rot, the advancing margin of the rot usually is bound by a dark line.
	The most characteristic tuber symptom is an extremely watery condition of diseased tissues, which turn brown or gray.
Integrated Management
	Rotate crops out of potatoes for at least four years to reduce Phytophthora and Pythium levels in the soil. Select well-drained fields and avoid excessive irrigation in the week prior to harvesting highly susceptible cultivars.
	Apply a systemic fungicide on susceptible cultivars when a field has a history of pink rot.
	Delay harvest when pulp temperatures are above 70 degrees F. Pick up windrowed tubers quickly and tarp loads to avoid overheating during warm harvest conditions.
	Store diseased lots separately from healthy lots. Keep temperatures below 45 degrees F. Provide good air flow to dry and cool infected tubers. Market diseased lots quickly to directly from the field.
	If considerable pink rot is present in the field, delay harvest to allow the full development of the symptoms in infected tubers so they can be graded out before the crop is placed in storage.

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.