How to Control Corn Earworms
Corn earworms (Helicoverpa zea) earned their name because the moth larvae primarily feed on sweet corn (Zea mays). You might also spot them eating tomatoes (Lycopersicon esculentum), which is why they're also called tomato fruitworms, as well as beans (Phaseolus vulgaris). The caterpillars feed on the shoots, leaves, kernels and fruit of those annual plants, often causing significant damage to tomatoes and beans and ruining the kernels on the tips of corn ears. Combining insecticide applications, oil treatments and the proper mechanical techniques often gives you effective control of corn earworm pests.
Dust With Carbaryl
Applying a thin, even layer of carbaryl dust to the exterior of corn ears helps eliminate earworms. Start treating the ears as soon the silks emerge and repeat applications once a week until the silks start turning brown. Begin treating other plants as soon as you spot the pests, repeating treatments every seven days until the worms disappear. Use the product's shaker bottle to lightly cover the tops and undersides of affected leaves with a thin, uniform layer of dust.
Take note of the preharvest interval days listed on the product's label. Sweet corn ears can be harvested just two days after a carbaryl treatment, but you have to wait up to three weeks to harvest beans. Wear protective clothing and eye wear to reduce your risk of chemical exposure. Apply dust on calm days when no rain is expected for 24 hours following treatment. Keep people and pets out of the treatment area until the dust settles. Carbaryl is highly toxic to honeybees, but you can reduce the risk of harming the pollinators by not dusting any blooming plants.
Treat With Bt
Bacillus thuringiensis, a natural bacterium that occurs in soils, helps control earworm pests on garden vegetables when you dust every three days. Bt targets caterpillars while having no effect on people, animals, plants or beneficial insects. Use 2 to 3 ounces of carbaryl dust for every 50 feet of growing area. Maximize control by thoroughly covering the husks or foliage.
Although Bt isn't as effective as broad-spectrum pesticides, it won't kill the beneficial insects along with the pests. You can also apply Bt up until the day of harvest, but wait at least 4 hours after application to reenter the treatment area. The bacteria break down in hot temperatures and direct sunshine, so wait until after 4 p.m. for optimal results. As always, wear protective clothing and eye wear when dusting with pesticides.
Treat With Mineral Oil
Eliminate earworms that have made it inside of corn ears by suffocating them with mineral oil. Use a medicine dropper or small squirt bottle to apply about 20 drops of oil to the inside tips of ears. Wait until the silks start drying and wilting to treat the worms, however. The oil can interfere with the pollination process if you treat the ears any earlier.
You can also trap young corn earworms before they can enter the ears by applying a few drops of mineral oil to the outside of the silks where they enter the husks. Start treatment when the silks first appear and repeat the process once every seven days until the silks turn brown. Mineral oil treatments can injure some corn varieties, so test the oil on a few ears of corn before applying it to your entire crop.
Use Mechanical Controls
Handpicking pests is a very effective solution for small gardens. Inspect your plants for corn earworms, picking up those you find and dropping them in a container full of soapy water. Prevent the pests from entering corn ears by clamping the ear tips closed with a clothespin or wrapping rubber bands around husk tips. Once corn earworm larvae enter the ears, it's relatively easy to open the end of the ear and remove the worms with a pair of tweezers.
In USDA plant hardiness zone 6 and warmer, overwintering earworms can survive in soil for as long as eight months. Tilling your garden in the fall helps reduce the number of overwintering pests by exposing the worms to hungry birds and the elements.
- Cornell University Growing Guide: Sweet Corn
- Mother Earth News: The Gardener's Predator Insect: The Corn Earworm
- Virginia Cooperative Extension: Corn Earworm on Vegetables
- Harvest to Table: Corn Earworm and Tomato Fruitworm Control
- UC Statewide IPM Online: Corn Earworm
- Cornell University Growing Guide: Tomatoes
- UC Statewide IPM Online: Corn Earworm
- Cornell University Growing Guide: Bush Beans
- University of California IPM Info: Corn Earworms