Biology
Powdery scab is a fungal disease affecting potato roots and tubers. Tubers develop slightly raised, purplish or brown lesions or pustules on the skin. Initially, the lesions are closed and blisterlike. They later split open to reveal powdery, dark brown masses of spores surrounded by the torn edges of the ruptured skin. In storage, a dry rot may be associated with the lesions. Powdery scab lesions are small (less than 1/8" in diameter) and nearly circular. These characteristics help distinguish them from common scab lesions. The roots of potatoes and related species may develop small galls or wart-like structures. Disease development is favored by cool, moist soils. The fungus can survive 3 to 10 years in the soil.
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