Physoderma brown spot is caused by the chytridiomycete fungus, Physoderma maydis (syn. P. zeae-maydis), which is closely related to the oomycete or water mold fungi, such as the downy mildews. This disease is normally an infrequent, minor disease in corn that we observe during most years to a low degree in Nebraska.

What is Physoderma brown spot?

Physoderma brown spot is a minor disease found in most areas where corn is grown and the leaf blight phase of the disease rarely affects yield. Numerous small, round, purple lesions on leaves, leaf midribs, leaf sheaths, or husk leaves are the typical symptoms.

Why are there brown spots on my corn?

Physoderma brown spot is caused by the fungus Physoderma maydis. Symptoms of Physoderma brown spot usually appear on mid-canopy leaves. Leaf lesions are numerous, very small (approximately ¼ inch in diameter), round to oval, yellowish to brown in color, and usually occur in broad bands across the leaf.