If you see small green worms wriggling around on your corn, chances are they’re corn earworms. Learn how to prevent corn earworm damage and naturally treat infected crops.
This article is part of our Organic Pest Control Series, which includes articles on attracting beneficial insects, controlling specific garden pests, and using organic pesticides.
The most common of sweet corn pests, corn earworm larvae are frequently found feeding in the tips of sweet corn ears. Organic corn earworm controls include choosing vigorous varieties with tight husks, treating ear tips with vegetable oil or a Bt pesticide, or simply breaking off the damaged part. Native to the Americas, corn earworms are now found throughout the world, especially in temperate regions where this sweet corn pest survives winter.
Most gardeners see this sweet corn pest in the first season of growing corn. The corn earworm is the larvae of a mottled tan night-flying moth common throughout North and South America. Corn earworms are most damaging to corn, but they can also bore holes into tomatoes, beans, peppers and a few other garden plants.
Most earworms are muddy-brown caterpillars, but they may be green, yellow, pink, reddish brown or dark gray. Fleshy caterpillars found feeding in the tips of ears of corn are probably corn earworms.
Mother moths lay tiny eggs on the emerging silks of corn ears, and from there the larvae hatch and burrow through the silks and into the tops of the corn ears. When you shuck the ears, one or more caterpillars may be found at the tips. In severe cases, this sweet corn pest feeds on the middles of ears as well.
On tomatoes, earworms feed initially on the foliage and save the juicy fruits for dessert.
Corn earworms overwinter as pupae from Zone 6 southward. When adults emerge in spring, some are transported northward on south winds. A few days after emergence, adult moths begin laying eggs on host plants. Eggs hatch in three to four days, and the larvae begin feeding. The larval stage lasts about two weeks in warm summer weather, or more than a month in spring and fall. This allows time for one or two generations annually in Northern regions, compared to up to seven generations in the far South. After the larvae attain full growth, they burrow into the soil to pupate — a state that can be as brief as two weeks in the summer or as lengthy as six months during winter hibernation.
Many natural controls are at work to offset the phenomenal reproductive capacity of corn earworms. Birds, bats, toads, spiders, and numerous predatory insects inflict a heavy toll on the earworm population. The minute trichogramma wasp is an important parasite, and the earworm helps control itself through cannibalism, especially in severely infested ears.
Many gardeners get good organic control of corn earworms by using eyedroppers or small squirt bottles to place a few drops of canola or olive oil in ear tips, as soon as the silks show signs of drying. You also can use a standard solution of Bt (Bacillus thuringiensis) or spinosad in the same way.
Frequently early corn is more seriously damaged by this sweet corn pest than midseason corn, mostly because robust midseason varieties have tight ear tips that prevent earworms from getting inside. Experiment with varieties and planting dates to find the best combination for escaping earworm damage in your area.
Corn earworms are too high for chickens to reach, but they can be employed to remove larvae that may be overwintering in the soil. You can also feed your chickens earworm larvae found in the tips of your corn.
Corn earworm damage disappears when you pop off the end of an infested ear, so you still get beautiful and delicious sweet corn.
Midseason sweet corn varieties with tight husks naturally resist earworm infestation.
In small plantings, you can open the end of an immature ear, remove the corn earworms with tweezers, and secure the husks back in place at the tip with a clothespin.