Corn Smut
Ustilago maydis
A fungal disease of corn that swells kernels and other plant parts into bizarre tumor-like galls filled with sooty black spores. It is the most widespread disease of sweet corn, more startling than serious in a home garden, and the young galls are even eaten as a delicacy called huitlacoche.
🔎 How to spot it
Look for swollen, tumor-like galls, from small to several inches across, on ears, tassels, stalks, or leaves. The galls start firm and silvery-white to greenish, then darken and rupture into masses of powdery, dark olive-brown to black spores. Galls that replace kernels on the ear are the largest and most obvious; those on leaves and tassels are smaller.
🥀 Damage it causes
Galls that replace kernels reduce the yield of the affected ears, and badly infected plants produce little usable corn. In a home garden the overall loss is usually minor and scattered, affecting a few plants or ears rather than the whole patch, though it looks dramatic.
🔬 What causes it
Corn smut is caused by the fungus Ustilago maydis, whose spores survive in the soil and crop debris for years and are carried by wind and splashing water to the plant. The fungus enters through wounds and through the silks, so injury from cultivation, hail, or insects raises the risk. It is favored by warm weather, 78 to 93 F, and by both low fertility and excessive nitrogen.
🛡️ Prevent it
Plant resistant or tolerant sweet corn varieties where available, and rotate corn to a new spot. Avoid wounding plants during weeding and cultivation, since wounds are entry points, and keep soil fertility balanced rather than over-applying nitrogen. Clean up and remove infected stalks and debris at season end.
🧯 If it is already here
There is no spray that cures corn smut, so the response is to cut out and remove the galls while they are still firm and pale, before they rupture and release spores, and destroy them rather than compost them. Removing galls early both limits the next spore load and lets you harvest them for the kitchen if you wish.
💡 Good to know
Corn smut is famous as much for the plate as the patch: the young, firm galls, known as huitlacoche, are prized in Mexican cooking. In the garden it is mostly a curiosity and a minor loss rather than a serious threat. Removing galls before they burst is the key to keeping spores from building up in the soil for future years.
🌱 Plants it affects
4 plants in the library can be affected by this problem
For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.