Corn Earworm Control
Description: Common in vegetable gardens throughout North America, the corn earworm (Helicoverpa zea) is one of the most destructive insect pests attacking corn. Damage occurs when the caterpillar feed on the tips of the ears, devouring the kernels and fouling them with excrement, sometimes destroying the silks before pollination is complete. The results are ears that are deformed and susceptible to mold and disease. The corn earworm is also a serious pest of cotton where it is known as the cotton bollworm. On tomatoes it is known as the tomato fruitworm.
Full grown larvae (1-1/2 inch long) are lightly striped and vary in color from a light green or pink to brown or nearly black. Adults are night-flying, dull greenish gray or brown moths (1-1/2 inch wingspan) with irregular darker lines and spots near the outer margins of the fore and hind wings. During the day they hide in nearby vegetation, but may occasionally be seen feeding on nectar.
Note: Adult moths are good flyers, and able to move long distances. Each year they migrate from warm southern areas to northern states where they do not overwinter successfully.
Life Cycle: In areas where this insect survives the winter, pupae hibernate in the soil. Adult moths emerge anywhere from February through June, depending upon temperatures, and deposit their eggs singly on corn silks and other plant parts. Each female can lay up to 3000 eggs, which hatch in two to ten days. When larvae emerge, they burrow directly down through the silks into the ear tip, becoming fully grown in 3-4 weeks. Corn earworm are extremely cannibalistic, which tends to limit the number of larvae to one per ear. Surviving larvae then leave the ear and enter the soil where pupation takes place. Usually two generations develop in the north, with as many as six in the extreme south.
Corn Earworm Control: Fall and spring tilling helps by exposing the pupae to wind, weather and predators. Use pheromone traps to determine the main flight period for moths, then release trichogramma wasps to destroy eggs. Beneficial insects, such as lacewings, minute pirate bugs and damsel bugs feed on corn earworm eggs and small larvae. Spray or inject silks weekly with Beneficial Nematodes to control larvae. Apply Dipel Dust (Bacillus thuringiensis) or Monterey Garden Insect Spray (Spinosad) to silks at 5-10% formation and continue weekly until tassels turn brown. Use botanical insecticides if pest levels become intolerable.
Tip: Squeeze an eyedropper full of mineral oil into the tip of each infested ear to suffocate feeding larvae. Some gardeners will include a botanical insecticide to this mix as an added punch.