Natural Control of Tomato Hornworms and Squash Pests

A gardener found green hornworms on tomatoes and small worm holes in squash, seeking natural control methods or pesticide recommendations.

Tomato Hornworm (Manduca quinquemaculata)

Identification

• Large green caterpillars (3-4" mature) with white V-shaped marks
• Distinctive rear "horn" (black on tomato hornworm, red on tobacco hornworm)
• Young larvae: pale green/white; blend perfectly with foliage
• Frass: large, dark green/black pellets on leaves/ground
• Adult: large sphinx moth (hummingbird moth) — nocturnal

Natural Control

• Hand-picking: Daily inspection; drop in soapy water or feed to chickens
• Bt kurstaki (Dipel, Thuricide): Spray foliage thoroughly; reapply weekly
• Parasitic wasps: Cotesia congregata lays eggs in hornworms; white cocoons on back = do not kill
• Companion planting: Dill, borage, marigolds may deter oviposition
• Soil solarization/tillage: Destroys pupae in soil (fall/spring)

Squash Pests: Identifying the "Small Worm Holes"

Several pests cause holes in squash:

Integrated Organic Program

For Tomatoes

1. Daily scouting June-September
2. Hand-pick all hornworms (except parasitized ones)
3. Weekly Bt spray if population high
4. Fall deep tillage to destroy pupae
5. Rotate nightshades yearly

For Squash

1. Row covers at planting until female flowers
2. Stem wrapping (foil/nylon) from soil up 12"
3. Weekly Bt spray on stem bases during moth flight
4. Destroy crop residues immediately post-harvest
5. Rotate cucurbits 3-year cycle

When to Consider Stronger Measures

• Large plantings (>20 plants) with heavy infestation
• Parasitic wasp activity absent
• Bt applications failing (resistance rare but possible)
• Commercial production requiring marketable yield

Then consider: Spinosad (organic, broader spectrum) or pyrethrin (botanical, short residual). Always follow label.

Key Resources

• Gardens Alive (gardensalive.com) for Bt products
• State extension services for local timing
• ATTRA Sustainable Agriculture for organic pest management guides

The original answer's recommendation of Bt (Dipel/MVP) and crop rotation remains the cornerstone of organic management for both pests.