University of Illinois Extension
Change Language

Corn Smut


Corn smut (Ustilago maydis) is a common problem on sweet corn. This disease over-winters as spores on the soil. In the spring these spores are splashed by rain onto the corn seedlings. Injury of any kind (insects, cultivation and so on) to the corn plants improves infection. The disease also infects better when the corn is grown on soils high in nitrogen (source can be either inorganic or organic).

During the summer the disease can spread and infect other sweet corn plant parts. The disease gets into the corn kernels via the silks. The infected kernels swell and cause the “popcorn like” appearance when weather conditions are suitable (usually dry, with temperatures between 79 and 93 degrees Fahrenheit). The smut at this stage is often eaten (used as a thickening agent in soups, stews and casseroles). Eventually the infected kernels rupture. The rupturing releases spores that fall to the soil to wait for next year’s planting. In home gardens, pick and destroy (burn or bury 1 foot or more deep) the infected ears before the infected kernels rupture.


Corn smut is a common problem on sweet cornCorn smut after infected kernels ruptured

Corn smut is a common problem on sweet corn