Corn earworm (Tomato fruitworm)—Helicoverpa zea
The corn earworm or tomato fruitworm is a common caterpillar pest of many vegetables and flowers. Newly hatched larvae have several rows of dark bristles on their backs. Older larvae are striped but their body color varies from green or yellow to brown and is not reliable for identification. Many short, whiskerlike spines cover the body surface.
Identification of species
Early plants are not as seriously damaged by earworms as are those planted for a later harvest. Female moths are attracted to plants in flowering and fruiting stages. They place eggs in a specific position. When available, corn silks are one of the earworm's preferred egg-laying sites; fresh silks are favored over older ones. On tomatoes, eggs are laid on terminal leaflets; in lettuce, a preferred site is the crowns of young seedlings. Eggs are spherical and are laid singly. Newly laid eggs are white, but they develop a reddish brown ring after about 24 hours. Larvae feed on fruit and leaves and drop to the soil to pupate. There are three or four generations per year.
Earworms feed on leaves, buds, and flowers of many vegetable crops. They destroy seedlings, bore into lettuce heads and bean pods, make deep watery cavities in fruit, and leave frass. On corn, larvae eat through kernels of ears and feed on the developing tassels in the whorls of the plant. Damage is usually limited to the first 2 to 3 inches of the ear.
On corn: Early planted corn is not as seriously affected as is late corn. Consider not treating, and simply cutting off damaged ends of corn at harvest. Applying a few drops of mineral oil with a medicine dropper to silks just inside each ear 3 to 5 days after silks first appear may be effective. Applications of insecticides, such as spinosad must be applied on silks within 3 days after first silks appear and at 3-day intervals until silks turn brown. Bacillus thuringiensis, a biological insecticide, may be dusted on silks every 3 days after 5 to 10% silk formation for partial control. Destroy culls and plants immediately after harvest.
On other vegetable crops and fruit: Handpick. Avoid spraying with insecticides. Bacillus thuringiensis, may kill 40 to 60% of the population but must be applied just after eggs hatch and before caterpillars enter fruit. Spinosad may also be effective. Plant early and harvest before late August. Disc or rototill plants immediately after harvest to reduce overwintering populations and prevent migration to neighboring crops.
Important natural enemies of the earworms include Hyposoter and Trichogramma parasites. General predators also feed on eggs and larvae.