Tomato Hornworm
Garden pest · Manduca quinquemaculata
Description
The tomato hornworm is the caterpillar of a large sphinx moth. Despite its name, it also feeds on other plants in the nightshade family, including peppers, eggplants, and potatoes. A mature caterpillar can reach about 4 inches (10 cm) long. It is green, blends remarkably well with tomato foliage, and can strip leaves from a branch in a short time. It may also chew tender stems and green fruit. Adult moths lay eggs singly on plants; the caterpillars feed for several weeks, then pupate in the soil. The adults are strong-flying moths that visit flowers for nectar. Hornworms are most noticeable in summer, though their timing varies with climate. A few caterpillars can cause conspicuous damage, especially on young plants, but healthy, established tomatoes often recover if the pests are found promptly. Hornworms are also food for birds and hosts for beneficial parasitic wasps.
Symptoms
- Holes in leaves
- Insects visible on the plant
- Stems chewed or cut through
How to Identify
Look for missing leaves, large irregular holes, and dark green or black droppings on leaves or the ground below. Follow the droppings upward and inspect stems and leaf undersides for a large green caterpillar. Tomato hornworms have white V-shaped marks along their sides and usually a dark horn at the rear. The closely related tobacco hornworm has diagonal white stripes and usually a reddish horn; both damage tomatoes and can be managed the same way. Unlike small leaf-chewing insects, one hornworm can remove substantial foliage quickly. White, rice-like cocoons attached to a hornworm indicate parasitic wasps are developing.
Prevention
Inspect tomato plants regularly, especially in summer, checking leaf undersides and the foliage above any droppings. Finding eggs or small caterpillars prevents extensive feeding. Keep weeds in the nightshade family away from the planting area, and remove spent tomato plants after harvest so remaining caterpillars are easier to spot. Where hornworms recur, lightly cultivate soil after harvest to expose some pupae, taking care not to damage roots or soil life. Fine-mesh row covers can keep egg-laying moths off young plants, but first check that no eggs or caterpillars are enclosed. Remove covers when plants flower or provide hand pollination. Encourage birds and parasitic wasps by maintaining a diverse garden and avoiding unnecessary broad-spectrum insecticides.
Treatment
Start by inspecting plants and hand-picking hornworms; drop them into soapy water or relocate them away from crops if appropriate. Check again over the following days for missed caterpillars and eggs. Leave any hornworm carrying white parasitic-wasp cocoons in place: the wasps will emerge and help control future pests, although that caterpillar may continue feeding briefly. If numerous small caterpillars remain, apply a product containing Bacillus thuringiensis var. kurstaki (Bt) to the foliage they eat, following the label. Bt works best on young caterpillars and has little effect on large ones. Reapply only as the label directs, particularly after rain. For severe infestations, a labeled spinosad product is another option, but it can harm bees and other beneficial insects; avoid spraying flowers and follow all label precautions. Hand removal is usually enough for a few hornworms.
Plants Affected
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