Gardening Articles: Edibles :: Vegetables

Corn Diseases, Insects, and Pests (page 2 of 4)

by National Gardening Association Editors

Insects

These are the insects most likely to affect corn, along with the best control measures for the home gardener.

Corn earworm is also known as the tomato fruitworm or cotton bollworm. This 1- to 2-inch-long caterpillar ranges from light green to purplish brown. Moths lay eggs on corn plants in early summer and larvae feed first on the silks, then on the kernels at the tip of each ear. The insect can prevent pollination, and it opens kernels to fungus invasion. To discourage this pest, select varieties with tightly closed husks. Earworms can be controlled somewhat by squirting mineral oil into each ear after silks have started to dry, using half a medicine dropper per ear. You can also spray the plant and silks with Bt. If earworm damage occurs, clip off the tip of the ear and any affected kernels. The rest of the ear should be fine to eat.

European corn borer is a 1-inch-long tan or brown caterpillar sporting rows of dark brown spots and a dark brown head. The moths fly mostly at night and lay eggs on the undersides of corn leaves in early summer. The hatched larvae bore into cornstalks and ears to feed. Broken tassels, bent stalks and "sawdust" around corn are all signs of borer damage. If you catch it in time, you can often cut out the borer from the stalk with no permanent damage. To prevent infestation, treat ears and leaves with Bt as soon as silk has partially emerged. Spray with an organic pesticide at five-day intervals from the time you first spot borer activity or when the tassels begin appearing. Make at least two applications for best results. Be sure to till or spade under crop residues at the end of the season so the borer has no place to overwinter.

Corn Sap Beetles are small, black beetles that spawn maggot-like larvae that eat into the kernels of roasting corn. Larvae are whitish and up to 1/4 inch long. The beetles are attracted to the scent of damaged corn, so preventing feeding by other pests helps keep them at bay. To prevent, plant resistant varieties and clean up all crop residues. Southern corn rootworms are small, yellowish grubs of the spotted cucumber beetle. They weaken corn plants by feeding on roots, causing the stalks to blow over easily in wind or heavy rain. Adults lay eggs around roots of cornstalks in the fall. The eggs hatch in spring. You can avoid damage from corn rootworms by tilling under cornstalks and rotating crops each year.

Corn Root Aphids are tiny, light green insects that feed on corn roots, causing the plants to be stunted and yellowed. The aphids overwinter in the nests of cornfield ants. The best way to control this pest is to plow the garden in the fall, destroying ant nests. Corn Flea Beetles are small but dangerous. Only 1/16th of an inch long, these jumping black beetles chew corn foliage and transmit Stewart's bacterial wilt. The pests abound during cool, wet periods and after mild winters. They hibernate in weeds and plant debris over the winter, so keep the garden and surrounding areas clean. Many of the later-maturing white corn varieties are resistant to wilt. To repel flea beetles, sprinkle a light dusting of wood ash over plants and soil.

Wireworms are slender, yellowish or brown larvae of click beetles. These 1/2- to 1 1/2-inch-long worms resemble a jointed wire. They damage corn plants by feeding on the roots. These pests are most often present in newly worked sod. Rotate crops and till or spade your garden thoroughly in the fall. Heavy infestations may require soil treatment with beneficial nematodes before planting.

Seed corn maggots are cream-colored and legless. The 1/2-inch-long larvae bore into sprouting seeds and prevent further growth. When early corn is planted in cool, wet soil, the slower germination makes the seeds more susceptible to maggot attack. If maggots are a problem in your area, delay planting until weather warms.

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