Tomato hornworm
In North America, hornworm caterpillars reach 10 cm (4 in) and can defoliate a tomato plant in days. They are superbly camouflaged; dark droppings on the leaves below are usually the first sign.
Pests
What it looks like
You find the droppings before the caterpillar.
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Stripped shoots Leaves eaten back to bare stems at the top of the plant. -
Large droppings Dark green or black pellets on leaves and soil. -
The horn A green caterpillar with white stripes and a horn at the rear. -
Wasp cocoons White rice-like cocoons on its back mean it is parasitised.
How to confirm it
Search where the damage is freshest.
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Follow the droppings
Look directly above fresh droppings.
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Look at dusk
They are easier to spot in low light or under a UV torch.
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Check the horn
A curved horn at the tail confirms it.
What to do
Pick them off.
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Hand-pick
Snip or pick caterpillars and drop them in soapy water.
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Leave parasitised ones
Caterpillars carrying white cocoons will die and release more wasps.
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Bt for young larvae
Bacillus thuringiensis works on small caterpillars.
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Till after harvest
Turning the soil destroys pupae overwintering there.
Prevent it next time
- Check tomato plants every couple of days in midsummer.
- Grow flowers for parasitic wasps.
- Rotate and dig over beds in autumn.
What not to do
Do not remove caterpillars carrying white cocoons; they are breeding the wasps that control the next generation.
In the growing guides
Where the guides mention it, with plant-specific advice.
Sources
- Hornworms, UC Statewide IPM Program