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Sweet Corn Pests - Corn Earworm
by Don Janssen, UNL Extension Educator
Sweet corn season is here, and there's nothing like eating freshly harvested ears – unless you find a worm when peeling back the husks! That unwanted intruder is usually the corn earworm, a caterpillar that eventually grows to 2 inches long. They vary in color, and may be green, brown, pink, black or various shades between these colors, with light and dark stripes along its sides and back. The head is always a yellow or light brown color, without any spots.
The adult corn earworm is a grayish-brown, night-flying moth with a wingspan of about 1 1/2 inches. Female moths prefer to lay their eggs on fresh corn silks, but will also choose buds and growing tips of young corn if silks aren't available. The tiny, light yellow eggs are laid singly. By the time the eggs hatch in a few days, they have turned to a dark brown. The little caterpillars crawl down the silks to the end of the ear to feed on the maturing corn kernels. Since they are cannibalistic, you typically will only find one in each ear of corn.
There are a number of options for controlling corn earworm in the home garden. There are some sweet corn varieties that show resistance to corn earworm damage. These include Country Gentleman, Stay Gold, Victory Golden, Silver Cross Bantam, and Silvergent. You may choose to plant mid-season varieties that will mature between moth flights so the ears will be less likely to be injured.
Chemical insecticides can also be used to protect the ears, but once the caterpillar has entered the ear, there is no effective control. To be effective, you need to completely cover the end of the ear so that when the eggs hatch, the young caterpillars will immediately contact a lethal dose of insecticide. Treatments must be reapplied every 3 to 4 days from when silks first appear until they become brown.
If you'd rather not treat the ears, you can always just cut off the damaged parts of infested ears, as the portion not fed on by the caterpillar is still perfectly good.
There are a number of natural enemies that attack corn earworm eggs. A number of tiny wasps parasitize the eggs, while minute pirate bugs eats the eggs and there is a virus that may infect and kill the eggs. There are also wasps that attack corn earworm larvae and pupae, however, these beneficial insects are not numerous enough to provide acceptable control.
Corn earworm has a wide range of tastes besides just corn. Other vegetables it will consume include tomatoes, beans, cabbage, and soybeans. It is referred to as the tomato fruitworm when found on tomato. Corn earworm prefers corn, but late in the season when corn plants are not as attractive, it may damage tomatoes and snap beans by eating into the fruits or pods.
University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office
Contact InformationUniversity of Nebraska-Lincoln
in Lancaster County
Web site: lancaster.unl.edu
444 Cherrycreek Road, Suite A,
Lincoln, NE 68528