Few things irk a tomato gardener more than a promising crop of healthy, juicy tomatoes ruined by fruitworms. The larva of the moth Helicoverpa zea is a major agricultural pest. It can feed on many different plants; hence the species has many common names depending on what the larva is consuming. Tomato fruitworm, when it consumes tomatoes. Cotton bollworm and corn earworm, when it consumes cotton and corn respectively, are its other well known aliases.
Adult moths have yellowish tanned bodies, a tan-colored head and bright green eyes. A solitary dark dot in the middle of each forewing coupled with several dark markings help distinguish them. The hindwings are pale in color and is enveloped by a dark brown border.
The moth lays eggs on the foliage of host plants both on upper and lower surfaces. Eggs are white or cream-colored, slightly flat, spherical shaped that darken before larvae hatch. Depending on the temperature, larvae hatch in 2-10 days.
The larva that hatches from the eggs is yellowish to white in color with a brown head. As the larva matures, its color can change to green, yellow, brown, red or black. Larvae are about 1 ½ inches long, have tan heads and alternating light and dark stripes that run lengthwise on their body. Their skin is coarse and has small, thorn-like projections called tubercles. The voracious larval stage lasts 14-21 days.
When the larvae are done feeding they drop down to the ground, enter the soil and transform into shiny brown pupae. Adult moths emerge from pupae in 10-14 days and start the cycle over. There are 2-5 generations per growing season.
The host plants of tomato fruitworms are a plenty. They love tomato, corn and cotton the most, yet don’t be surprised to see them on eggplant, okra, peppers, soybeans, beans, squash, sunflower and tobacco.
Damage is caused only by the larvae. Although larvae can feed and develop on leaf tissue, the preferred feeding sites in most crops are the reproductive sites, such as tomato fruit and corn ears. On corn, the larvae feed on fresh silk before moving down the ears eating kernels and leaving trails of excrement. In tomatoes, evidence of damage is usually a visible black hole at the base of the fruit stem. They will also eat the flower buds and chew holes in the leaves. It is much the same, though less common, on the other types of plants.
Organic Control and Preventative Measures:
1. Trim tomato plants so that there are no leaves or stems any lower than 12 inches from the ground. This allows ample airflow from ground up and helps keep away many insects from dwelling in your plants and feasting on your precious tomatoes.
2. Look for signs of fruitworm infestations regularly. Adults lay eggs on both sides of leaves, usually close to blossoms. Ridding of eggs can reduce fruitworm populations drastically. Handpick and destroy fruitworm eggs and larvae as you find them.
3. Prevent fruitworms from boring into fruit by covering fruit with fine netting. Better yet, cover plants with floating row-covers to prevent adults from laying eggs on host plants.
4. Avoid growing tomato near corn or any other aforementioned crop, unless your intention is to use them as a trap crop. If one plant gets infested, you could have your garden teeming with fruitworms!
5. Encourage natural predators of the tomato fruitworm. Big-eyed bugs, minute pirate bugs, lacewing and damsel bugs feed on tomato fruitworms. Attract them by planting goldenrod, daisies, alfalfa and stinging nettle. Trichogramma wasps and Hyposoter exiguae wasps parasitize the eggs and larvae respectively. Planting dill, parsley and asters attracts the parasitic Trichogramma wasps. These wasps are available commercially and can be ordered.
6. Bacillus thuringiensis (Bt), a microbial biological control, is effective against tomato fruitworms among several other pests. Use Bt at the first sign of fruitworm eggs. Apply as directed by the product label. Bt works by paralyzing the digestive system and infected fruitworms stop feeding within hours.
7. Neem oil and biodegradable insecticidal soaps have been found to deter fruitworm infestations. Spinosad, a natural, broad-spectrum biological insecticide made from soil microbes works on tomato fruitworms too.
8. Cultural control: Remove and destroy infected plants. Roto-till the soil at the beginning and end of the season to expose and destroy overwintering fruitworm pupae. Rotate crops by planting tomatoes in a different area of your garden each year. Companion planting with garlic has been said to repel many pests.
9. Dusting plants with diatomaceous earth or Rotenone can help deter fruitworms from moving about the plant.