Early blight – Alternaria solani, fungus
Tubers are not generally attacked by this fungus, but infection can occur when tubers become inoculated with spores before and during harvest. Lesions on the exterior of tubers are irregular in shape and range from I/4 to 2 inches in diameter. These brownish black spots may be slightly sunken (approx. 1 / 16 in. deep) and have a raised purplish border. When tubers are cut through the lesions, they appear as a dry, dark brown rot, which is generally much shallower than that of late blight. Lesions are sharply set off from healthy tissue by a corky layer. Storing tubers below 41 ° F will stop further development of decay, and forced–air ventilation will reduce the chance of spread in storage. Foliar fungicide applications should be made when the disease first appears on leaves. Good vine killing, with a delay of a minimum of 7 days before digging, will also reduce the opportunity for tuber infection.