Powdery mildew of Potatoes

Powdery mildew is not always as noticeable on potatoes as on other plants. It first appears on potatoes as brown lesions of various sizes on stems and petioles. Lesions coalesce to form short streaks or stippled patches. The white powdery coating typical of powdery mildews on most other hosts frequently does not develop on potatoes, but if the air is moist, diseased leaves eventually may be covered by it.

Leaves and stems are killed, and only the tip of the plant may remain green. In severe cases, vines collapse. Infection and vine collapse may be over large areas of the field. Late in the season, small black specks may develop in the powdery growth. These are chasmothecia, the overwintering fungal bodies.