Corn smut, also known as common smut, is a common disease of sweetcorn caused by the fungus Ustilago maydis. This disease rarely kills corn plants, but usually causes the production of smaller ears. Corn smut commonly develops on the tassels, ears, leaves, and shoots of corn as a gall. The disease is not systemic, and galls form only where spores land and infect. The fungus survives winter in corn debris or in the soil. Spores produced in the spring are windblown or rain-splashed to healthy plants, where they either penetrate the plant surface directly or enter through natural openings and wounds. Plants are most commonly infected early in the growing season, at the active growing points.
Galls range from the size of a pea to five inches in diameter. Galls on the leaves usually remain small, while those on the ears may be large and fleshy. Galls consist of fungal material and enlarged plant cells. When young, the outsides of the galls are silvery-white to greenish-white with a firm interior. At this stage, the galls may be cooked and eaten, and in some countries they are considered a delicacy. As the galls mature, they turn brown to black and become spongy. Eventually, black sooty spores rupture through the outer coverings of the galls and fall to the soil, where they survive for several years.
There are no chemical controls for infected plants. Control is limited to a few cultural practices. Remove and dispose of smut galls before they rupture and release the black sooty spores. Remove and destroy all plant debris in the fall and practice crop rotation the following year. Avoid plant injury during cultivation, as this promotes disease development.
Chad Behrendt, Crystal Floyd