How to Treat and Prevent Tomato Hornworms in Your Garden

How to Identify Tomato Hornworms

Tobacco and tomato hornworms are large, slow-moving green caterpillars that come out in hot weather and can devour tomato plants in no time. Evolution has given them the ultimate camouflage: their green bodies blend in perfectly with tomato leaves when they cling to the stems of your plants. All too often, gardeners don't even notice these guys until they've already caused significant damage.

One thing sets hornworms apart from other green caterpillars, and that's their horn, a little protrusion at the end of their bodies. It looks scary, but it's actually harmless.

Hornworms themselves are anything but harmless to your plants. These ravenous pests can destroy tomatoes, peppers, and eggplants at an alarming rate. Fortunately, they're pretty easy to control, even without turning to a bunch of sprays.

Quick Hornworm Facts

• Hornworms are large green caterpillars with a horn-like tail.
• These pests chew on the leaves and fruits of plants and can completely defoliate crops in just a few days.
• Their favorite plant is tomato, but they'll also eat peppers, eggplants, potatoes, and dill.
• Physical removal of any pests you spot is the most effective form of treatment. Check your plants daily.
• The best way to prevent hornworms is to invite lots of beneficial insects into your garden.

Tomato Hornworm Damage

You’ll know you have hornworms in your garden if you notice a lot of chewed or missing leaves on your plants (usually starting at the top). You might also notice partially devoured fruits.

A sure sign a hornworm is nearby is spotting a bunch of pellets that look like blackish-green Nerds candies or teeny tiny grenades (that’s their poop).

Tomato Hornworm Host Plants

• Tomatoes
• Tomatillos
• Eggplants
• Peppers
• Potatoes
• Dill

Tomato vs. Tobacco Hornworms

There are two types of hornworms that gardeners in North America commonly deal with, though both are often referred to as tomato hornworms. (You are, in fact, more likely to deal with tobacco hornworms.) They both feed on Solanaceae plants like tomatoes and peppers, and reach about 4 to 5 inches in length.

Technically, tomato hornworms are the ones with a black horn and white V-shaped markings along their sides.

Tobacco hornworms have a red horn and parallel white stripes lined with little black spots along their sides.

Life Cycle of Tomato Hornworms

1. Hornworms are introduced to your garden by adult tomato hornworm moths, also called sphinx moths or five-spotted hawk moths. They're mottled gray-brown moths with a wingspan of about 4 to 5 inches.
2. In late spring, the females deposit smooth, oval-shaped, light green eggs on the bottoms of leaves of host plants.
3. These eggs hatch within a week, and the larvae, aka the baby caterpillars, begin to feed. Small hornworms are yellow to white in color with no markings.
4. Caterpillars become full-grown within 4 to 6 weeks. During that time, they're feasting on your plants.
5. Once mature, caterpillars burrow into the soil to transform into pupae.
6. In warmer climates, they emerge as five-spotted hawk moths 2 weeks later and begin a second generation by mid-summer.
7. These moths deposit more eggs on host plants.
8. The second generation of caterpillars feed on host plants until late summer or early fall.
9. They fall to the soil, where they overwinter as pupae.
10. They emerge as adult moths in the spring, and the whole cycle begins anew.

How to Get Rid of Tomato Hornworms

Here is the 5-step process I use to treat hornworms organically:

Step 1: Prune & Clean

The first measure to treat your plants is to remove all of the damaged leaves and clear the soil around the plant of any debris. Things like fallen leaves and large pieces of bark give hornworms another place to hide.

Step 2: Handpick

Search for green caterpillars in the surrounding area and on the stems and leaves of your plants. Since hornworms are hard to find during the day, I recommend taking a blacklight out to your garden at night. Hornworms will glow green, making them super easy to spot.

Pick off any pests you find and drop them into a bowl of soapy water, leave them as offerings near bird feeders, or feed them to your chickens. If you're squeamish, wear a pair of gloves (and remember, these pests can't sting or bite you).

Step 3: Spray

After you’ve removed as many hornworms as possible, spray your plants with garlic barrier. You can make your own by crushing a few cloves of garlic and mixing with 1 quart of water. Let it sit for 1 to 2 days. Strain the liquid into a spray bottle.

Treat the tops and bottoms of leaves as well as the stems thoroughly. The best time to spray is in the early morning or late afternoon.

Step 4: Repeat

Repeating steps 1 through 3 every week is very effective, especially if you have a smaller garden that's easy to search. I usually only move on to step 5 as a last resort.

Step 5: Treat

In the case of a severe infestation, you might turn to Monterey B.t., or Bacillus thuringiensis, a soil-dwelling bacterium that kills caterpillars but has no effect on honey bees or birds. B.t. must be reapplied to the plant's leaves after rain, and it has to be ingested by the hornworms and caterpillars to be effective.

Note: I always try to control pests with pruning and cleaning before I turn to pesticides, even organic ones.

How to Prevent Tomato Hornworms

It's a good idea to check your tomato plants for missing leaves every week, if not every day, during the warmer months. There are also a number of things you can do now to deter hornworms and/or minimize their destructive potential.

Grow Basil & Marigolds Near Tomatoes

Basil is a wonderful companion plant for tomatoes. Its strong scent repels a number of pests, hornworms included. Another great (and equally strong-scented) companion plant for deterring the moths that lay hornworm eggs is marigolds, particularly French marigolds.

Plant Trap Crops

Trap crops are a pesticide-free way to manage pests in your vegetable garden. Dill is a great trap crop to keep hornworms off tomato plants. The hornworms will congregate on the dill stems, making them easy to hand pick.

Turn Over Soil at the End of the Growing Season

I generally avoid tilling my soil to protect earthworms and beneficial microorganisms. But it's a good idea to do a little tilling at the end of your season if you've dealt with hornworms to destroy any burrowing pupae that might overwinter there. Hornworms only burrow about 3 to 4 inches below the surface, so you can do some light tilling without destroying the other lifeforms in your soil. Tilling can kill up to 90% of the hornworm pupae.

Remove Weeds

There are several weeds related to tomatoes that hornworms will also use as host plants, including horsenettle, jimsonweed, and nightshade. Either pull these weeds around your garden space or use them as trap crops for hornworms.

Invite Natural Enemies to Your Garden

Tomato hornworms have many natural enemies, meaning there are lots of bugs out there that want to eat them or use their bodies as hosts for their young (brutal but true). Ladybugs and lacewings, for instance, feed on young hornworms and hornworm eggs. Paper wasps and birds feed on caterpillars of all sizes.

And then there are parasitic wasps, which lay their eggs inside hornworms. The larvae that hatch from those eggs feed on the hornworm until they're ready to pupate. If you see a hornworm that looks like it's covered in little grains of rice (white during the day, magenta under a blacklight), leave it be. It's past the point of being able to cause major harm to your garden, and it's supporting future generations of beneficial insects.

The best way to attract these beneficial insects to your garden is to plant lots of flowers like sweet alyssum, marigolds, zinnias, cosmos, coreopsis, salvia, and anise hyssop. Intersperse different types of flowers for a mix of colors, textures, and heights.

Another great way to attract garden "good guys" is by letting your herbs flower. Beneficial insects adore flowering herbs like lavender, mint, sage, and lemon balm. Parasitic wasps love the umbrella-shaped flowers of cilantro and dill.

Finally, you can attract more birds to your garden by setting up a little bird bath or fountain.

Once you've attracted these natural enemies to your garden, protect them by avoiding pesticide usage, even organic and "safe" sprays like Neem oil and diatomaceous earth.

Tomato Hornworm FAQs

Are tomato hornworms good or bad?

Hornworms can cause considerable damage to plants in a matter of days, so they're regarded as vegetable garden pests. They look intimidating for caterpillars, but they can't cause any harm to humans. You can handle them—horn and all—without concern. If you're squeamish, wear a pair of gloves before hand picking them from your plants.

What do I do if I find a tomato hornworm?

First, remove hornworms by hand and toss them into a bowl of soapy water or set them on the bird feeder as a little offering. Some gardeners use scissors or pruners to cut them in half. If you keep chickens, toss the hornworms into the coop for a protein-rich treat. Next, take steps to prevent further damage. There are a number of organic control methods you can apply without resorting to chemical insecticides.

What attracts tomato hornworms?

The moths that lay tomato hornworm eggs look for gardens filled with food for their young as they mature into caterpillars. Tomatoes are top of the menu, but they'll also feed on other plants in the Solanaceae (nightshade) family, including potatoes, eggplant, peppers, and tobacco.

Can a tomato hornworm sting you?

Despite the scary appearance of their little horn, hornworms can't bite or sting you. It's safe to handle them with your bare hands, if you feel so inclined.

Where do tomato hornworms hide during the day?

Hornworms like to hang out on the underside of stems and leaves on your tomato plants to avoid the heat and sun during the day. It's hard to spot them thanks to their tomato-green camouflage. They become more active at dusk, and it might be easier to spot them then.

Do birds eat tomato hornworms?

Many birds, including cardinals, chickadees, house wrens, finches, and chickens enjoy a nice little hornworm snack.

What are the white eggs on my tomato worm?

It may look like the hornworm is carrying its own eggs on its back, but those are actually the pupae of braconid wasps that are using the hornworm as a host—basically a living incubator for their young. The baby wasps will feed on the hornworm until it dies and then grow into adult wasps. Make sure to leave hornworms covered in these little parasitoids be so that your garden will soon be filled with beneficial wasps. (We like this kind of wasp, I promise.)

Treat & Prevent Hornworms Without Sprays

Hornworms are a great reminder that your garden is a little ecosystem all on its own. The best way to manage pests is actually by increasing the diversity of life inside, not by decreasing it. That's how we work with nature to practice safe, organic pest control.

Once your garden has become a welcoming haven for beneficial insects, you can deal with any hornworm issues that may arise in just a couple easy steps—no pesticides required.

Sources

University of Minnesota Extension

Farmers' Almanac

Research Gate: "The Effects of biotic interaction between tomato and companion plants on yield"

University of Wisconsin-Madison

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