Impact
Early blight is caused by the fungus Alternaria solani. Foliar infections can greatly reduce leaf area, limiting tuber yields. Early blight is a common and economically serious disease that occurs annually in the San Luis Valley.

Early blight foliar symptoms.		Early blight tuber symptoms.

Descriptions and Symptoms
	Leaf lesions are circular and dark with a yellow border. As lesions expand, an angular appearance develops due to confinement by the leaf veins.
	Target-like or concentric rings of raised and lowered dead tissue are typical in large lesions.
	Infection usually begins on older, lower leaves and moves slowly into the upper canopy.
	Tubers are infected at harvest by fungal spores on the soil surface.
	Tuber lesions are circular- to irregular-shaped, slightly sunken and dark-colored with a raised purple to brown border. Tuber tissue under the lesion is dark and dry, appearing corky or leathery.
	After extended storage of infected tubers, moisture loss form the lesions can result in shrivelling.
	Early blight spores overwinter in soil, crop residue and on infected tubers.
Integrated Management
	Manage the crop for optimal crop fertility and soil moisture to slow disease development.
	Scout for foliar lesions at emergence and continue weekly.
	Monitor degree-day reports provided by Agro Engineering to determine timing of fungicide application.
	Apply fungicides uniformly to the plant canopy. Fungicides are not available to treat tuber infection on commercial potatoes.
	Minimize tuber injuries to limit tuber infection. Proper skin set is the most important barrier to infection.
	Cool storages rapidly if tuber infections are anticipated. Keep in mind conditions faboring suberization also favor tuber blight development.
	Manage storage to avoid free water on structural surfaces.

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.