What Are the Caterpillars in My Corn?

Growing corn is a popular summer gardening prospect. Sweet corn is easy to propagate and the stalk as well as the sweet corn on the cob is relished by gardeners and farm stand customers. Generally, corn is plagued by few pests, however, there are two main caterpillar species that will feed on the corn grain head. These pests are similar in appearance, lifestyle and in the damage the inflict on the corn.

The Fall armyworm will infest the corn ear itself. Unlike the corn earworm, this insect will also affect the corn plant as it grows, damaging the leaves and the young corn. The armyworm is a thick worm similar in appearance to a small sausage. The worm is striated in slate gray and oak brown stripes. It has rows of black spots running in rings around its body. Four distinct spots rest at the top of the caudal end.This pest is found in the southern regions but spreads to the zone 6 (and 5) area in summer. Armyworms bore through the corn ear leaving a telltale hole in the corn.

The corn earworm is a light green caterpillar with segments along its body appearing as if they had been tied off with string. A yellow strip runs down the side, and its feet are tiny pointed pins set beneath the segments. These are the most common worms to infest the corn ear itself and are very difficult to control once established. The moth lays the eggs in the silk where they hatch. The corn earworm then bores down through the silk, unlike the armyworm, which enters through the husk. In heavily infested areas corn species with tight ear husks are grown, or the young grain heads are treated with insecticides at first tasseling.

Sprinkle the young corn tassles with diatomaceous earth. Repeat this after heavy rains. Parasitic wasps will attack the larvae, and these predators can be purchased from agricultural stores. Several parasitic flies (generally tachinidae) will kill the larvae. These flies appear similar to typical black flies, but are elongated with wasp- or hornet-shaped bodies. Parasitic nematodes will destroy the pests, and these tiny worms are located in the soil where the caterpillars pupate. Consult organic pest control sites, universities or farming organizations for these products.

Spinosad, carbaryl and other marketed compounds are available for purchase. Consult a farm, garden or agricultural store for the proper pesticide for your area and infestation. All pesticides (and particularly those applied to food plants) carry some risk and specific dosing and application recommendations.