How to Get Rid of Hornworms on a Tomato Plant

Keep your tomato plant healthy by eliminating hornworms.

Hornworms often make their way onto tomato plants and cause serious damage. Hornworm larvae, which can grow 4 inches long, typically do the most damage. As the larvae mature, they turn into moths, which lay their eggs on the plant, creating another generation of hornworms on the vegetation. These large caterpillars feast on the plant's leaves and leave behind their black droppings or "frass." Eliminating the hornworm from your plants is laborious but worth the effort.

Things You'll Need

• Tweezers
• Scissors
• Bucket of water
• Bacillus thuringensis (Bt)
• Lemon balm, parsley, dill or fennel plants
• Rototiller

Instructions

1. Pick the hornworms off the plant with tweezers or your fingers. Either cut the worms in half with a pair of scissors or drop them into a bucket of water to drown. Look closely for the worms, as their pale green color often blends in with the rest of the plant, making them difficult to spot. Hand-picking hornworms is typically easier at dusk, as the caterpillars tend to stay close to the plant's interior during the day to avoid the sun. After the sun is gone, they venture to the outside of the plant, where they are more visible.

2. Spray the larvae with Bacillus thuringensis, also known as Bt. This bacterium produces crystal proteins, which are toxic to the larvae. While Bt is usually sprayed directly on the plant, read the directions for best results.

3. Plant lemon balm or parsley near your tomato plant to attract parasitic wasps, which lay eggs on hornworms. The eggs hatch larvae and feed off the hornworms from the inside out, eventually killing the hornworm. Planting dill and fennel attracts ladybugs and lacewings, which eat hornworm eggs and early larvae.

4. Till the soil around the plant. Full-grown larvae leave the plant and burrow into the soil to pupate. Tilling kills the pupae that are taking up residence in the soil.

Tips & Warnings

• Look for hornworms on your tomato plants in July and August. Look for eggs on the leaves and on the hornworms themselves.

• Check other plants in the garden for hornworms, as they also frequent eggplant, potato and pepper plants.

• Bt is often available at gardening centers and home improvement stores.

References

• "University of Minnesota Extension"; Tomato Hornworm; S.J. Wold-Burkness, et al.
• "Colorado State University Extension"; Tomato Hornworms; Judy Sedbrook
• University of California-San Diego: What Is Bt?
• Grinning Planet: Natural Pest Controller (Other Than Caller ID)