Keep the leaves dry when watering and avoid overhead sprinkler irrigation. Remove plant debris from the garden after harvest, since many diseases survive on plant debris from year to year. Do not grow potatoes in the same area year after year, but rotate with crops other than tomatoes. Common diseases of Irish potatoes in home gardens are described below. This is a potentially serious disease of potato and tomato, caused by the fungus Phytophthora infestans .
Late blight is especially damaging during cool, wet weather.
The fungus can affect all plant parts. Young lesions are small and appear as dark, water-soaked spots. These leaf spots will quickly enlarge, and a white mold will appear at the margins of the affected area on the lower surface of the leaves. Infected potato tubers have a dry, corky rot that may be brown or reddish. Tubers are symptomless at the initial stages of infection but often develop symptoms in storage.