Corn Earworm / Tomato Fruitworm
Corn earworm (sometimes called tomato fruitworm) (Helicoverpa zea) larvae feed on all plant parts, but prefer tomato and pepper fruits especially. Larvae bore deeply into the fruit to feed, resulting in watery internal cavities filled with cast skins and frass (feces). Unlike on corn, where one larva is found per ear, a single larva can enter several fruits during feeding and development.
Corn earworm eggs are small, round, and are almost transparent white in color. The larva is a brown-headed caterpillar with alternating dark and light stripes running lengthwise on the body. Adult moths are tannish brown with a 1 ½-inch wingspan.
In Utah, there are up to three generations of corn earworm each year. The first generation of moths either come from overwintering pupae (southern and central Utah), or migrate each season from the south. After mating, females lay eggs on fresh leaves. The larva feeds on leaves or crawls into the fruit, and feeds for 10 to 14 days, then exits and drops to the ground. They burrow 2 to 5 inches deep into the soil and pupate, and moths emerge to form the second generation. Pupae formed in late summer may overwinter in warmer climates, otherwise they are killed by cold winter temperatures.
- Tunnels in kernels
- Direct damage to stem
- Premature fruit ripening
- Fruit rot from secondary fungi
- Unmarketable fruit
Monitoring early in the season (starting in early summer) is important to prevent damage. Inspect leaves above and below the highest flower cluster for eggs. When fruit is present, check for damage and presence of larvae. Check several plants in 4-5 locations.
Avoid planting tomato, pepper, and eggplant near post-silking corn fields. When corn silks turn brown, fruitworm moths will seek out other nearby hosts for egg-laying.
Disk, plow, or remove plant debris, cull fruits, and weeds, to eliminate overwintering host sites and to destroy infested fruits and pupating larvae.
Natural enemies include parasitic wasps (Trichogramma spp.) which parasitize fruitworm eggs, and generalist predators such as lacewings (Chrysopa spp. and Chrysoperla spp.), big-eyed bugs (Geocoris spp.), damsel bugs (Nabis spp.), and minute pirate bugs (Orius spp.) which attack eggs and young larvae. Trichogramma pretiosum is available from commercial insectaries.
Although larvae may remain partially unprotected in the fruit and be exposed to insecticides when moving from fruit to fruit, it is best to target treatment towards eggs and newly hatched larvae before they enter the fruit in large numbers.
Residential options include: Bt (Bacillus thuringiensis), spinosad, or pyrethrins
Commercial options include: Bt, spinosad, chlorantraniliprole, and many others