Garden pest
Tomato hornworm
A single one can strip a tomato plant of its leaves overnight.
Tomato hornworm is in its active season now — scout your plants this week.
How to identify tomato hornworm
Fat green caterpillars up to 4 inches long — about the size of your finger — with white V-shaped side stripes and a soft horn or spike on the tail end. The horn looks fierce but cannot sting.
Their green matches a tomato stem almost perfectly, so you can stare right at one and miss it. That camouflage is why most of the damage happens before anyone spots a bug at all. The near-identical tobacco hornworm has diagonal white stripes and a red horn; the fix is the same for both.
Attacks: Tomatoes, Peppers, Eggplant, Potatoes
Life cycle: Large gray-brown 'hummingbird' moths lay single green eggs on leaf undersides in late spring; caterpillars feed for 3-4 weeks, then drop to pupate in the soil and overwinter there.
Signs of tomato hornworm
What you actually see on the plant — usually before you spot the pest itself.
- Whole stems stripped bare of leaves near the top of the plant
- Dark green or black droppings the size of a peppercorn on lower leaves and the ground
- Chewed, ragged leaf edges and the odd bite taken out of a green fruit
Organic control, least-toxic first
Start at the top and only move down if you need to. Physical and cultural fixes come before any spray.
- Hunt the droppings, then hand-pick
Don't look for the caterpillar first — look for the dark pellet droppings, then work up the plant to the hornworm feeding right above them. Pull each one off and drop it in soapy water.
- Scan at night with a UV flashlight
Hornworms glow bright green under UV light, which turns a 10-minute evening pass into an easy find when they're impossible to see by day.
- Spray Bt on the young ones
Bacillus thuringiensis (Bt) is a natural bacteria that kills small caterpillars in a day or two and is safe on food crops up to harvest. Follow the product label for rate and timing.
- Leave any hornworm wearing white rice-like sacs
Those are the cocoons of a parasitic braconid wasp that is killing the hornworm from the inside. Leave it be and the wasps hatch to hunt more hornworms for you — free, self-renewing control.
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One rule for any product you spray: follow the label. The label is the law, and it is the tested, safe rate for your plants — homemade mixes and dish-soap sprays are not, and can scorch foliage.
Prevent it next season
- Turn over the top few inches of soil in fall to expose and destroy buried pupae before winter
- Rotate tomatoes to a new spot so any surviving pupae hatch away from their food
- Interplant dill, basil, or marigold to draw in the parasitic wasps and other predators
Questions about tomato hornworm
What does hornworm damage look like?+
Whole stems stripped bare near the top of the plant, ragged chewed leaf edges, and dark pellet droppings the size of a peppercorn on lower leaves and the ground.
What spray kills tomato hornworms?+
Bt (Bacillus thuringiensis). It's a natural bacteria that kills caterpillars within a day or two and is safe to use on food crops right up to harvest.
What are the white things on a hornworm?+
Cocoons of a beneficial parasite wasp that is killing the hornworm from the inside. Leave that caterpillar alone so the wasps hatch and go hunt more hornworms for you.
Plan a garden that fights back
Healthy, well-spaced plants shrug off pests that flatten a crowded bed. PlotToTable sizes your beds, spaces every crop, and flags the pests that hit what you grow.