Tomato Hornworm
TreatablePest · does not spread · also called tobacco hornworm
A hornworm can defoliate a tomato branch in a night and still be almost impossible to see, because its colour and stripes match the foliage precisely. The reliable method is to look for the damage and the droppings, then look directly above them.
What it looks like
A green caterpillar up to four inches long with white diagonal stripes and a curved horn on its rear end. Entire branches are stripped bare overnight, and dark green pellets of frass collect on the leaves below.
How to confirm it
- Whole stems stripped to bare stalks, not scattered holes.
- Dark green or black pellets of frass on the leaves beneath.
- Look above the frass, not around the damage — that is where the caterpillar is.
- A blacklight torch at night makes them glow, which is by far the easiest way to find them.
What to do
- 1Pick them off by hand. This is genuinely the most effective control and takes minutes.
- 2Leave any hornworm carrying rows of white rice-like cocoons on its back. Those are parasitic wasp pupae — that caterpillar is already dying and will produce wasps that kill more.
- 3Bt (Bacillus thuringiensis) works on younger caterpillars if numbers are high.
What it gets confused with
One observation settles each of these.
Cabbage worms are small, velvety and found on brassicas, not tomatoes, and they make ragged holes rather than stripping stems.
Preventing it next time
- Till the bed in autumn to expose overwintering pupae.
- Check plants every few days in midsummer.
Plants affected
Check these two things first
- Push a finger into the soil, two knuckles deep. Wet soil plus a wilting plant means too much water, not too little — and it is the commonest reason a plant is dying. Dry soil plus crisp leaves means the opposite. The leaves look nearly identical either way, so the soil is what tells you.
- Turn a damaged leaf over. Half of all diagnoses live on the underside: fuzz means downy mildew, fine webbing means spider mites, clusters of insects mean aphids. Nothing on the top of a leaf is as informative.
Most garden problems are cosmetic and resolve without treatment. Reach for a spray last, not first.