How to Identify and Get Rid of Tomato Hornworms
How to Identify and Get Rid of Tomato Hornworms
Big, fat, and green! Here are tips on how to identify, control, and get rid of tomato hornworms in your garden.
What Are Tomato Hornworms?
If you’ve ever grown garden tomatoes, chances are you have dealt with these green caterpillar pests. They can be found in most any region of the US and can ruin your tomato crop in record time; they also feed on eggplants, peppers, and potatoes. They can blend in quite easily with the green foliage and feed non-stop, creating spotty and chewed leaves and fruit.
Tomato hornworms live according to the following life cycle:
- In late spring, large adult moths lay eggs on the undersides of foliage, which will hatch within a week.
- Caterpillar larvae will feed from 4–6 weeks before creating a cocoon for overwintering in the soil. If the weather is warm enough, larvae may only burrow for as little as 2–3 weeks.
- Moths will emerge in the spring, and will then lay eggs once again. More than one generation a year may be possible in warmer climates.
Tomato hornworm moth (female). Look out for the moths in late spring. Photo by Didier Descouens/Wikimedia Commons.
How to Identify Tomato Hornworms
Tomato hornworms can be up to 5 inches long—which can be quite a shock when you first come across one! They do the most damage in the caterpillar, or larval, stage. They are pale green with white and black markings, plus a horn-like protrusion stemming from their rear. (Don’t worry, they aren’t able to sting!) The caterpillar also has eight V-shaped stripes on its green body. Tomato hornworms come from a mottled brown-gray moth.
The larvae blend in really well with the plant greenery. Just get used to a daily patrol, looking for hornworm eggs and small caterpillars. Here are some cues of infestations:
- Look closely at the TOP of your tomato leaves for dark green droppings left by the larvae feeding on the leaves. Then look at the underside of leaves and you’ll find a hornworm.
- Look for stems missing some leaves and wilted leaves hanging down. You may find white cocoons and their hornworm hosts nearby.
Tomato vs. Tobacco Hornworms
There are a few species of hornworms that inhabit North American gardens, including tomato hornworms (Manduca quinquemaculata) and tobacco hornworms (Manduca sexta). Both species feed on common garden plants like tomatoes, potatoes, peppers, and eggplants. Here’s how to tell which caterpillar is which:
- Tobacco hornworms have parallel white stripes; tomato hornworms have white V–shaped markings.
- Tobacco hornworms have black spots lining each of their stripes; tomato hornworms do not.
- Tobacco hornworms have a red “horn” on their tail end; tomato hornworms have a black horn.
Can you tell which hornworm this is? (It’s a tobacco hornworm! Notice the white stripes with dotted black lines and a red “horn.”)
Tomato Hornworm Damage
If you see leaves with large holes and severe defoliation, devoured flowers, and/or scarring on fruit surfaces, you have tomato hornworms. The fruit also might be damaged by sunscald because of the reduced foliage.
Control and Prevention
How to Get Rid of Tomato Hornworms
- Handpicking is an excellent tactic for control if you have the time and patience, or a small garden. The caterpillars are not dangerous and cannot sting. If you are squeamish about crushing these large insects, drop them into soapy water instead (or feed them to your chickens, if you’ve got a flock).
- If the hornworm population or the area of your garden is too large, insecticides can be a useful control. You can use the organic pesticide Bt (Bacillus thuringiensis), which is a bacterium that acts as a stomach poison on some insects (but doesn’t harm other plants or animals). Please check with your local Cooperative Extension for a list of approved insecticides in your area.
A tobacco hornworm covered with parasitic wasp eggs.
Prevent Tomato Hornworms
- Till soil at the beginning and end of each gardening season to destroy overwintering larvae. Tillage has shown to cause up to 90% mortality.
- Keep wasps around; they’re beneficial insects which feed on hornworms and act as a biological control. You may see hormworms with parasitic wasp larvae attached, which look like grains of rice (see picture, above). These attacked hornworms will continue to feed for a little while, but will soon succumb to their hitchhikers, so it’s wise to leave them alone and let the wasps carry out their life cycle. Alternatively, remove infected hornworms and place them far away from your garden. This way, the wasps will still do their job, but the hornworm won’t continue to damage your crops.
- To keep hornworms away from your tomato plants next year, try interplanting dill or basil; marigolds are also an excellent companion plant and keep many pests away.
See the Almanac Garden Pest and Disease Library for information on all your common pest problems.