Powdery mildew

Symptom

The disease is caused by wind-dispersed fungi. Powdery mildew is not always as noticeable on potatoes as on other plants. Initially, brown lesions of varying sizes appear on the stems and petioles of the potato plant. Lesions coalesce to form short streaks or stippled patches. Unlike many other host plants, the characteristic white, powdery growth of powdery mildew often does not develop on potatoes unless the air is moist. The stems and leaves eventually die off, leaving only the shoot tips green. This results in malformed tubers and a significant reduction in both yield and quality. As the disease progresses, it can spread across entire potato fields. Late in the season, the lesions may exhibit small black specks, which are overwintering fungal structures known as chasmothecia.