Early Blight Of Potato. Early blight or target spot is caused by alternaria solani, an opportunistic fungus that attacks older leaves as the plant ages or when the plant is under stress. The disease affects leaves, stems, and tubers, and can reduce yield, tuber size,.

Early blight is a very common disease of both potato and tomato. Early blight is caused by the fungus alternaria solani and thrives in warm, humid conditions.