By Dr. Harold Willis
There are dozens of kinds of insects that attack all parts of the corn plant—roots, stalk, leaves, and cob. As we have said, they are just part of nature’s clean-up crew, eating the sick plants. Healthy plants will have little or no damage and even produce special chemicals that repel at least some pests. One such natural repellant is called DIMBOA, which is formed when corn tissue is injured and which repels young European corn borers, as well as the fungi that cause northern corn leaf blight infection and gibberella stalk and ear rots.
Insect pests also have their own natural enemies: other insects, parasites, and birds that keep them under control—if they aren’t poisoned themselves by over-use of insecticides. If insecticides have to be used to save a crop, effective kill can often still be obtained by reducing the dosage. But many pests can be adequately controlled by non-toxic methods, many of which were used decades ago (see box on next page).
But the same as for weeds, the best long-range pest control is to have good soil which produces healthy, naturally resistant plants. Also, some hybrid varieties are more resistant to certain pests than others, and of course, some genetically engineered varieties contain the Bt gene and are resistant to corn borers.
- Control of insects attacking seeds (seed corn maggot, wireworms, and seed corn beetles): delay planting until conditions are good for rapid germination (wheel-track plant in dry years); replant between old rows if great damage (then cultivate out the worst stand); fall plowing; drain low spots.
- Control of root-eating insects (corn rootworm larvae, corn root aphids, white grubs, and grape colaspis larva): rotate or plant between old rows to escape large rootworm population; early plowing, disking, delayed planting, and extra phosphorus fertilizer for grape colaspis; disking to kill weeds and ant colonies for aphids; fall plowing and milky spore disease inoculant for white grubs.
- Control of insects feeding on underground part of stalk (wireworms, billbugs, sod webworms, and cutworms): plant other crop than corn if breaking sod; early fall plowing; reseed if necessary, then cultivate out worst stand; drain wet areas; early spring plowing and planting for cutworms.
- Control of insects feeding on corn leaves (armyworms, wooly bears, corn leaf aphid, corn flea beetle, grasshoppers, corn blotch leaf miner, chinch bug, cereal leaf beetle, 2-spotted mite, and thrips): early planting and resistant varieties for flea beetle; fall plowing and natural enemies for grasshoppers; don’t plant beside small grains for cereal leaf beetle; natural parasites and fungus disease for aphids; control of thrips, mites, wooly bears, and corn blotch leaf miner seldom necessary; no good control for armyworms (but they will avoid a healthy crop).
- Control of insects feeding in whorl, stalk, and ear (European corn borer, corn earworm, corn rootworm adults, stalk borers, fall armyworm, corn sap beetle, and picnic beetle): plant resistant varieties, midseason planting (not early or late), fall plowing, plow under or pulverize dead stalks, and bacterial disease inoculant (Bt) for European corn borer and stalk borers; plant resistant varieties for corn earworm; control other insects and diseases for sap and picnic beetles (they only feed on injured, unhealthy plants); no good control for fall armyworm (but they will avoid a healthy crop).
Source: How to Grow Top Quality Corn/(Advances in Corn Production, 1966; and Modern Corn Production, 2nd ed., 1975)