If you’ve ever grown tomatoes, chances are good that you’ve dealt with these green caterpillar pests. There are two main garden pest species, tomato hornworms and tobacco hornworms, which can be found in most regions of the U.S. and in southern Canada. Both species can ruin your tomato crop in record time! They also feed on other plants in the Solanaceae (nightshade) family: eggplants, peppers, tobacco, and potatoes. They blend in quite easily with the green foliage and feed non-stop, creating spotty and chewed leaves and fruit.
They consume entire leaves, small stems, and sometimes chew pieces from fruit. Despite their large size, hornworms are often difficult to spot because of their protective coloring. Growers will often find large areas where feeding has occurred before they see this garden pest. Damage is most often noticed in midsummer and continues throughout the remainder of the growing season
Tomato Hornworm Control
- Because they are so large hornworms are most often controlled in home gardens by handpicking. Once removed from the plant, they can be destroyed by dropping them into a bucket of soapy water.
- Beneficial insects including lacewings, braconoid and trichogramma wasps and ladybugs attack the eggs. For best results, make releases when pest levels are low to medium.
- If populations are high, use a least-toxic, short-lived natural pesticide to establish control, then release predatory insects to maintain control.
- Both Safer Garden Dust (Bacillus thuringiensis, var. kurstaki) and Monterey Garden Insect Spray (Spinosad) are very effective, especially on the young caterpillars (larvae).
- Apply 100% organic Diatomaceous Earth for long-lasting protection. Made up of tiny fossilized aquatic organisms, that look like broken glass under the microscope, DE kills by scoring an insect’s outer layer as it crawls over the fine powder. Contains NO toxic poisons!
- If pest levels become intolerable, spot treat with a fast-acting organic insecticide. For best results, apply to the undersides of leaves and deep into the plant canopy where insects hide.
- Roto-tilling after harvest destroys overwintering pupae in the soil. This is especially effective since pupae are large and not buried very deeply in the soil. Results have shown that greater than 90% mortality is caused by normal garden tilling.
PREVENTING TOMATO HORNWORMS
To keep hornworms away from your tomato plants next year, try interplanting dill or basil; marigolds are also an excellent companion plant.
You may see hormworms with parasitic wasp larvae attached, which look like grains of rice, these attacked hornworms will continue to feed for a little while, but will soon succumb to their hitchhikers, so it’s wise to leave them alone and let the wasps carry out their life cycle.
Alternatively, remove infected hornworms and place them far away from your garden. This way, the wasps will still do their job, but the hornworm won’t continue to damage your crops.
Another beneficial insect, like ladybugs and green lacewings, may feed on young hornworms or hornworm eggs.
Till soil at the beginning and end of each gardening season to destroy overwintering larvae. Tillage has shown to cause up to 90% mortality.