Worldwide distribution. On potato, tomato and relatives, and weeds. An important disease.
Irregular patches of rot on leaves; white cottony growth with spores on undersides. Leaves yellow, shrivel and fall. Tubers rot. Spread in wind and rain and in “seed”.
Cultural control: certified seed; remove volunteers; drainage; 2-3-year crop rotation; spacing to aid air movement; drip irrigation; limit amount of N; early tolerant varieties, avoid cull piles; collect and burn trash after harvest.
Chemical control: chlorothalonil, mancozeb, or copper; alternate with, e.g., dimethomorth, metalaxyl, cymoxanil, or strobilurins. Phosphorus acid either alone or with chlorothalonil.