Organic Pest Control for Tomato Hornworms

Principles of Organic Pest Management

• Organic standards set by the U.S. Department of Agriculture forbid the use of synthetic pesticides. Most organic producers use a practice called integrated pest management (IPM) that seeks long-term prevention and control of pests using the least toxic strategies available. Controlling tomato hornworms in your garden fits well within the IPM framework.

Prevention

• The first step in IPM requires you to put in place cultural practices that prevent the pest from arriving or causing damage to your plants. To prevent tomato hornworms, keep the garden weeded, and remove alternate weed hosts from the vicinity of your tomato plants. Tomato hornworms will also feed on horsenettle, jimsonweed and nightshade, members of the same family as the tomato. After harvesting your tomatoes, remove the vines from the garden and till or turn the soil to destroy any caterpillars overwintering in the soil.

Handpicking

• Check your tomato plants twice per week in the summer for tomato hornworm caterpillars. Because they're large and easy to spot and identify, the most effective way to control the tomato hornworm is to handpick the caterpillars from your plants. Bring a bucket of soapy water into the garden with you and drop the caterpillars in as you find them.

Beneficial Insects

• Several insect species feed on or parasitize the tomato hornworm in the wild. Strategies to attract these insects will provide you with willing allies in your quest to control tomato hornworms in your garden. Ladybugs, lacewings and paper wasps feed on young caterpillars. Pollen-producing flowering plants feed adult ladybugs and lacewings and encourage their presence in your garden. Take care not to destroy paper-wasp nests unless they threaten human safety.

  Parasitic wasps lay their eggs inside of tomato hornworms. When the adult wasps emerge, they kill the caterpillar. Leave parasitized caterpillars in your garden, as the emerging wasps will parasitize additional caterpillars.

Organic Insecticides

• Two substances permitted by organic agriculture standards can help to control tomato hornworms if other controls are impractical. Insecticides are typically a last-ditch strategy in an IPM program. Insecticidal soap will kill caterpillars, but only if it comes into direct contact with them. Insecticidal soap won't harm most beneficials. Bacillus thuringiensis ssp. kurstaki is a bio-pesticide -- a disease that afflicts only caterpillars. Caterpillars must ingest the bacteria in order for the product to work. Insecticidal controls work best while caterpillars are small.