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Pest, Disease & Weed Timing CalendarsTomato Hornworm Calendar
Tomato hornworms are easy to overlook when small and hard to ignore once large. A weekly check in midsummer finds them early.
Key points
- Hornworm pupae overwinter in soil, and moths lay eggs on tomato and relatives in summer.
- Look for droppings and stripped leaves, then search close by for the caterpillar.
- White cocoons on a hornworm mean parasites at work, so leave it.
- Hand picking and fall tillage reduce numbers in small plantings.
What is the tomato hornworm life cycle?
The tomato hornworm is the larva of a large moth often called a hawk moth or sphinx moth. Pupae overwinter in the soil. Adults emerge in late spring or early summer, depending on the region, feed on nectar and lay eggs on the undersides of leaves of tomato and related plants such as pepper, eggplant and potato. Larvae hatch, feed and grow quickly, then drop to the soil to pupate.
Extension pages from Illinois, Utah State and Colorado State describe this cycle, and note that the number of generations depends on the length of the warm season. Check your state's page for local patterns.
For example, if you plant tomatoes in late spring in a region with a short warm season, expect one main generation of larvae in midsummer, and plan your heaviest checks for that window rather than all season long.
When should you begin checking tomato plants?
Start checks once plants are established and keep going through the summer. Damage often shows up in midsummer, when larvae from the first generation reach large size. In longer-season areas a second generation can appear later in the season.
Do not rely on a calendar date. Watch for the first signs, such as missing leaf tips, dark droppings on lower leaves and a large moth visiting evening flowers.
Look at plants in the evening as well, since adult moths feed at dusk and their presence near flowers is a useful early sign that egg laying is under way.
How do you find hornworms?
Hornworms are green and blend in well with foliage, so look for the evidence first. Large, dark green or black pellets on leaves or on the ground below plants, stripped leaves and gnawed green fruit are clues. Then search the plant above the damage, since the caterpillar is usually close.
Evening checks with a flashlight can help, but extension pages mainly recommend a careful visual search of the plant, working from the damage upward. Check lower leaves too, since the first small larvae often feed there before moving up as they grow and the damage becomes more visible.
- Dark droppings on lower leaves or soil
- Stripped leaves at the top of the plant
- Gnawed green fruit
- Eggs on undersides of leaves
Why do you sometimes see white cocoons on hornworms?
Small white rice-shaped cocoons on the back of a hornworm are parasitic wasp pupae. The wasp larvae fed inside the caterpillar, which will soon stop feeding and die. Leave parasitized caterpillars in the garden, since the next generation of wasps will help control hornworms.
Recognizing parasitized caterpillars keeps you from destroying a natural ally and can save you work. Gardeners often move parasitized caterpillars to a spot away from the plants to let wasps emerge, though simply leaving them in place is enough.
What control steps fit a garden or small farm?
Hand picking is effective on small plantings, and a quick weekly walk is enough for most gardens. Tilling the soil after harvest can expose and destroy overwintering pupae, where tillage fits your system. Rotation and spacing from last year's plantings also help.
For larger plantings, ask your extension office about biological and other products labeled for the crop.
If you find a hornworm on a plant next to pepper or eggplant, check those crops as well, since moths lay eggs on all three.
What about products and labels?
Any product used on tomatoes must follow its label, which is the law. Check pre-harvest intervals, since tomatoes are harvested repeatedly, and protect pollinators such as bees visiting flowers. Applicator licensing varies by state. Your county extension office can give current local recommendations.
Keep a short log of first moth, first eggs, first larvae and plant damage. Compare to next year. Pull out spent plants at season's end and till or turn the soil to expose pupae to weather and predators.
What mistakes cause hornworm damage to be missed?
The most common is looking at the plant without looking for evidence first. Large caterpillars hide in plain sight, so droppings and stripped leaves are the better signs. Another is destroying caterpillars with white cocoons, which removes a natural control. A third is skipping nearby peppers and eggplants.
Photograph unusual caterpillars before you remove them. Some other caterpillars look similar, and identification matters before you decide anything. Your extension office can help with a clear photograph and the date and location.
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.