Worldwide distribution. On maize and sweet corn. There are two kinds, both may occur on maize at the same time. Oxalis species (woodsorrels) are also hosts. Important disease, more severe on sweet corn.
Round, oval and irregular pustules, powdery, brown, becoming darker as the plant matures, on leaves, leaf sheaths and stems. The pustules are most common on the leaves where they are scattered on both surface.
Spread is by wind-blown spores.
Cultural control: resistant varieties; weed, especially Oxalis; remove volunteer plants; collect and burn trash after harvest.
Chemical control: not needed on maize; on sweet corn use chlorothalonil or mancozeb.