Hornworm Control: Skip Cornmeal, Use Bt Instead

Cornmeal for Hornworms? No Evidence It Works

A gardener heard cornmeal kills tomato hornworms. Research shows no scientific support for this method. Don't waste time or cornmeal.

Proven Organic Control: Bacillus thuringiensis (Bt)

Bt is a bacterium that produces proteins toxic to caterpillars but safe for humans, pets, birds, and beneficial insects. Commercial formulations:

• Dipel, Thuricide, Caterpillar Attack, Biobit, Javelin, Xentari
• Apply at first sign of feeding (small holes, frass).
• Reapply after rain or every 7–10 days.
• Thorough coverage (undersides of leaves) is critical.

Additional Hornworm Strategies

1. Hand-pick – large, easy to spot; drop in soapy water.
2. Parasitic wasps – Cotesia congregata lays eggs in hornworms; white cocoons = parasitized. Leave these alone.
3. Companion plants – dill, borage, marigold may repel moths.
4. Crop rotation – avoid planting tomatoes in same spot yearly.
5. Soil solarization – reduces pupae in soil.

Excellent Resource

ATTRA Organic Tomato Production Guide – comprehensive pest/disease tables, varieties, cultural practices.

Bottom Line

Cornmeal is a myth. Bt + hand-picking + habitat for wasps = effective, organic hornworm management.