Tomato fruitworm, Helicoverpa zea
Tomato fruitworm moths are about 1 inch long and are white or tan with irregular wing markings. These moths are nocturnal and can often be found resting beneath foliage during the day. Females lay white or pale green, spherical eggs singly on younger leaves and buds of hemp. As the eggs mature, they become yellow and gray and develop ridges. The eggs are very small, about 0.5 mm (0.02 inches), and each female moth can lay as many as 25 eggs in one day. Young larvae are small and dark with black bristles and, after hatching, are typically concentrated near plant reproductive structures. Later instars are about 25.5 mm (1 inch) long and are green, brown, pink, yellow, or a combination of these colors. They also have alternating dark and light stripes running lengthwise along the top of the thorax and abdomen, and brown or black heads with rows of dark bristles or bumps along the body. Pupae are brown or dark red.
- The tomato fruitworm, also referred to as the corn earworm or bollworm, is a major pest of corn in Colorado. Other susceptible vegetables include asparagus, cabbage, cantaloupe, collards, cowpea, cucumber, eggplant, lettuce, lima bean, melon, okra, pea, pepper, potato, pumpkin, snap bean, spinach, squash, sweet potato, tomato, and watermelon.
- Adults are moths that can travel up to 300 miles in one night. In northern Colorado, tomato fruitworm populations do not survive the winter and are reestablished annually when moths migrate north from suitable overwintering sites.
- Monitoring for tomato fruitworm moths can be done with pheromone traps and is recommended to help growers determine when control measures are necessary.
Caterpillar of tomato fruitworm on peanut. Tomato fruitworm is a highly polyphagous pest that can feed on a wide range of vegetables, hemp, cotton, and ornamental plants. Monitoring for adults and caterpillars can help inform decisions related to pest management. Image credit: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
Adult (left) and caterpillar (right) of tomato fruitworm on soybean. Image credit: John C. French Sr., Retired, Universities:Auburn, GA, Clemson and U of MO, Bugwood.org
Caterpillar of tomato fruitworm feeding on soybean. Image credit: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
Caterpillar of tomato fruitworm feeding on peanut leaf. Image credit: John C. French Sr., Retired, Universities:Auburn, GA, Clemson and U of MO, Bugwood.org
Caterpillar of tomato fruitworm boring into a squash. Image credit: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
Life history and habits
Tomato fruitworm overwinters in southern Colorado as a pupa in soil, though the weather in some areas may reduce survival of overwintering pupae. The temperatures in northern Colorado are not suitable for winter survival and are repopulated each growing season after moths emerge and migrate north from overwintering sites. The moths actively lay eggs on host plants in the summer. There are two generations each year, possibly more depending on temperature.
Caterpillars tunnel into tomatoes and peppers which reduces their quality and makes them less marketable. They also feed on leaves, stems, and flowers, producing holes in these plant structures which can reduce product yield and quality.
Begin inspecting plants for tomato fruitworm eggs, caterpillars, and signs of feeding injury in late June or early July before populations reach peak densities. Tomato is very attractive to this pest and a good plant for initial scouting in fields and gardens. To detect eggs, inspect leaves below the highest cluster of flowers. Caterpillars can be dislodged and counted by shaking the plant over a piece of white paper or cardboard. Visually inspect plants for the presence of excrement (frass), wilting leaves, and tunnelling in buds or fruit, all of which are signs of a tomato fruitworm infestation. Frass may also be present on the ground beneath the plant. Blacklight and pheromone traps can be used to monitor adult densities.
Removing larvae by hand is a time consuming but effective management strategy. Larvae can be killed by crushing or by placing them in a jar with alcohol or nail polish remover. Rototilling or disc tilling after harvest will help reduce the overwintering population.
There are several natural enemies of tomato fruitworm. Insect predators of corn earworm larvae include lacewings, minute pirate bugs, and damsel bugs. Trichogramma wasps are naturally occurring parasitoids that reproduce by parasitizing caterpillars, killing them as a result. While these wasps can be purchased and released in fields, the efficacy of this technique has been limited in neighboring states like Utah. Conserving naturally occurring populations of these beneficial insects is considered a more cost-effective and practical strategy since releasing commercially available Trichogramma wasps requires specific timing and maintenance of wasp populations.
For vegetables other than corn, treating with chemicals is not recommended. The bacteria Bacillus thuringiensis can provide some control when applied after egg hatch and before caterpillars tunnel into fruit.
Alston, D., S. Olsen, J. Barnhill. 2011. Corn Earworm. Utah State University – Extension. Available https://extension.usu.edu/pests/research/corn-earworm
Kuhar, T., C. Philips, H. Doughty, A. Alford, E. Day. 2019. Corn Earworm on Vegetables. Virginia Cooperative Extension. Available https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/3103/3103-1537/ENTO-312.pdf
University of California. (n.d.). Corn earworm (Tomato fruitworm) – Helicoverpa zea. University of California – Statewide Integrated Pest Management Program. Available https://ipm.ucanr.edu/PMG/GARDEN/VEGES/PESTS/cornearworm.html#:~:text=Destroy%20culls%20and%20plants%20immediately,and%20before%20caterpillars%20enter%20fruit.