Answer: The symptoms sound very much like "Black Scurf", a fungal disease caused by Rhizoctonia. This disease causes hard, black lesions on the surface of the tuber. It doesn't affect the quality of the tubers, but they may not store as well as tubers uninfected by the disease. Rotate your potato crop, avoid overwatering, especially early in the season, and be sure to purchase certified disease-free seed potatoes.
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