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.
The fungus produces a foul odor when infection is severe. Fungal spores are spread between plants and gardens by rain and wind. A combination of daytime temperatures in the mid-70 s with high humidity is ideal for infection. Keep foliage dry. Locate your garden where it will receive morning sun.