Gardening Articles: Care :: Pests & Problems
Corn Diseases, Insects, and Pests
by National Gardening Association Editors
Most of the trouble gardeners have with corn is easily controlled. Diseases aren't much of a problem, and insects can easily be kept in check. Birds and four-footed visitors who want to share your corn harvest can be kept out with any number of scare-off devices and fences. Prevention can be 100 percent of the cure. If you sow your corn in well drained soil that has balanced nutrient levels, youre on the road to having healthy plants. Healthy plants can withstand nibbling or insect damage better than weakened ones. In many cases, a crop that's healthy will often be spared disease and insect attack altogether.
A very important step you can take for disease-free corn is to clean up all the cornstalks as soon as the harvest is over. Till healthy cornstalks into the soil as additional organic matter, or, if you prefer, shred, compost or simply discard them. Dealing with old cornstalks will prevent many diseases and insects from overwintering, which is crucial to the health of crops grown in future seasons.
Stewart's Bacterial Wilt can affect sweet corn at any stage, but is most harmful to young plants. It causes dwarfing and wilting of the plants, and the tassels often develop early and die without completing pollination. Leaves develop yellow-brown streaks and wavy edges. The leaves of young plants may dry out, and the stem eventually dies. This wilt is often characterized by a yellow slime on the inner husks and in the stem. Bacteria overwinter in the gut of the corn flea beetle. This disease is prevalent after a mild winter, when more disease-carrying flea beetles have survived. To prevent an outbreak, clean up all crop residues, rotate your corn crop each year, plant resistant varieties and control corn flea beetles.
Root Rot is caused by fungi in the soil and shows up as stunted plants or irregular plants with rotten roots. You risk root rot when planting seed in cold, damp soil. Use treated seed, plant on raised beds if soil drainage is a problem and wait until the soil temperature is 55° F before planting.
Corn Smut is caused by a soil fungus, and can strike corn anywhere its grown. Smut looks awful, but its not a disastrous condition. Smut is edible and actually is sought after by gourmet chefs. In the early stages of the infection, grayish white, spongy growths called "galls" usually appear on the corn ear or tassel. As these galls ripen, they turn black and eventually burst open, releasing powdery spores that spread the smut. The disease thrives in hot, dry weather and often infects weak or injured plants first. To prevent, rotate crops, and if you notice any galls, pick them and burn them before they blacken and burst. This will halt the smut's spread and is often all it takes to keep the disease in check from one season to the next.
Southern Corn Leaf Blight is another fungal disease. It is characterized by tan streaks or lesions on the leaves, and may cause early seedling death, mold-covered kernels or rotten cobs. A similar disease, northern corn leaf blight, results in grayish green or tan lesions on the leaves and reduced yields. These fungi overwinter in infected seed and plant debris. Plant resistant varieties, using healthy, certified disease-free seed. Rotate crops and remove or till under crop debris. If the disease has been severe in your area, check with your local Extension agent for a preventive fungicide program. In 1970 this blight reached epidemic proportions, wiping out 15 percent of the total United States corn crop, for an estimated loss of one billion dollars.