Fresh-picked corn is one of the true pleasures of summer, but for many gardeners, bringing a crop of corn to harvest is a challenge. Corn takes up a lot of space in the garden and must be planted in a block so wind can pollinate it. It is a heavy feeder, requiring frequent fertilizer applications. Several diseases affect corn, and unfortunately, the only control for most of them is to destroy the affected corn plants. Practice good cultural practices, such as crop rotation and proper plant spacing, to increase your odds of a healthy corn harvest.
Corn smut is one of the most unusual diseases to infect the vegetable garden. It is caused by the fungus, Ustilago maydis, and causes large fleshy galls (bumps) to form on the corn ears and stalks. The galls are white to gray when small, but turn brown with black smut when mature. They range in size from 2 to 5 inches wide, and render the corn inedible.
There is no chemical control for corn smut and it spreads readily through spores that move through the air or overwinter in the soil. Rotate corn annually and remove any galls from the stalks as soon as they appear. Discard plant debris in the fall to minimize the spread of corn smut.
Rust is a common corn disease, but rarely causes more than aesthetic damage. It produces red colored lesions on the upper leaves and stalks of the corn plants, but generally doesn’t affect the corn. Plant corn two weeks after the last frost in full sun. Space corn at least 12 inches apart so air circulates freely and water it as needed to keep the soil evenly moist. Healthy corn is less likely to become infected with rust.
Corn Seed and Root Rots
Seeds planted too early in the season in cold, wet soil are prone to rotting due to fungi found naturally in the soil. These seeds fail to germinate or young seedlings may be stunted and grow poorly. Root rot occurs after the plants are growing, but is also caused by fungus and exacerbated by wet, cool soils.
To control seed and root rots, plant high-quality seeds. Buy seeds treated with a fungicide if you live in an area prone to seed rot. Plant corn in loose, light soil to ensure good drainage, and wait until after the last frost to plant.
Virus Corn Diseases
Maize dwarf mosaic virus causes stippled or mottled green blotches on the upper leaves, while maize chlorotic dwarf virus causes pale streaks on the leaves. Both stunt corn plants and reduce yields.
There is no chemical control for these viruses. Remove infected plants immediately and remove all debris after the harvest. The viruses overwinter on nearby weeds and grasses, so removing those as well can prevent the spread of the diseases.
Corn Leaf Blights
Leaf blights cause gray, tan or brown lesions on leaves, and may eventually infect the ears, as well. Buy disease-resistant corn seed if you’ve had problems with leaf blight and rotate the corn crop, waiting three or more years before planting in the same spot again.
Want to learn more about corn diseases?
Corn Crop Diseases from University of Minnesota Extension