Facts about Tomato Hornworms and How to Control Them in Your Garden

Tomato hornworms are very large caterpillars, measuring up to 4 inches long. They are the most destructive pests of tomatoes, peppers, potatoes, and eggplants. Hornworms eat leaves, stems and sometimes chew holes in fruits. The damage is completely defoliating and often easy to notice.

Despite their large size, tomato hornworms are not easy to spot. Their camouflaging color blends them well into the leaves. Defoliated plants and dark green or black poop are a classical sign of their presence in your garden. A close inspection of your plants will typically reveal them.

Tomato hornworms are highly destructive, their feeding can result in tomato plants dying. If this is the first time you are encountering them in your garden, this guide explains where they come from, what they turn into, and how you can control them to protect your plants.

Where do tomato hornworms come from?

Tomato hornworm is a larva stage of the five-spotted hawkmoth. The life cycle begins in spring when females mate and lay oval greenish eggs on the undersides of the leaves of the host plant. In about 5 days, the caterpillars hatch and begin feeding until late summer or early fall.

The larvae keep transforming through several stages to their full growth in just 3 to 4 weeks. The mature caterpillars eventually drop off the plants and burrow into the soil, transforming into pupae. Adult moths emerge in about 2 weeks and they begin mating and laying eggs again.

By mid-summer, the second generation of tomato hornworms begins. The moths deposit eggs and within a few days, caterpillars hatch. They feed until early fall and then pupate. The pupae remain in the soil through winter and emerge as adult moths in spring.

How to identify tomato hornworms

As said, it can be difficult to spot tomato hornworms in your garden due to their camouflaging color. If you come across defoliated plants and dark droppings around the base of the stems then know that tomato hornworms are around. However, you can spot them if you look keenly.

Unlike other caterpillars, tomato hornworms are big, probably the largest. They are about 3 to 4 inches long with a horn-like projection from their rear. They are typically green in color with white markings down their sides. Eggs are smooth, oval, and light green. 

While their body features make it difficult to notice them, they thrush and move especially during active feeding which happens at dawn, dusk, and night. The best way to spot them is by using a UV flashlight. They tend to glow like small bulbs when you shine UV light on them.

Adult hummingbird moths are large insects with wide wings, 4-5 inches. They appear mottled gray-brown with a few yellow spots on the sides of the abdomen. The hindwings have alternating light and dark bands. The insect entirely feeds on nectar from various plants.

How to get rid of tomato hornworms

Tomato hornworms are relatively easy to control when identified earlier. They may be found on the leaves, stems, or even on the ground near the plants. Here’s what you can do to get rid of them.

Handpicking and disposing of

Handpicking is the most straightforward way of dealing with tomato hornworms in home gardens. Although they don’t sting or bite, some people may feel scared to touch them. Simply wear thick gardening gloves and remove them from the plant, just don’t squish them.

After picking hornworms off the plants, drop them into a bucket of soapy water to drown them. Alternatively, place them in a sealed plastic bag and throw them away. Because they are not poisonous, you can also feed them to your chicken.

After removing the hornworms,  you should keep searching your garden for more of them. It takes about 4 to 5 days to completely eradicate them. Remember to check the underside of the leaves for eggs and destroy them.

Introduce natural predators

You can also rely on natural enemies of tomato hornworms. Just introduce predatory insects, such as lady beetles and green lacewings. They often eat hornworms in the egg stage and young caterpillars. Paper wasp is also another option, it feeds on most types of garden caterpillars.

Many parasitic insects also target hornworms as hosts. One of them is the braconid wasp. The insect lay their eggs on the caterpillar allowing the hatching larvae to feed on the inside of the hornworm until the wasp pupates. The cocoons will appear like white grains on the back of a hornworm.

The hornworm dies as soon as the parasitic wasps emerge from the cocoons. Once mature enough, they also look for another hornworm to parasitize. This continues until all the caterpillars in your garden are gone. 

Use natural pesticides

Insecticides should be the last resort in dealing with tomato hornworms, spider mites, and other pests in your garden. Natural pesticides like insecticidal soap and neem oil are low-risk and won’t kill beneficial insects. However, these products must directly contact pests to be effective.

When using pesticides, follow the instructions on the label. Experts always recommend testing on a small section of the plant a few days before making a full application. For best results, you must apply your insecticide thoroughly including the underside of the leaves.

How to prevent tomato hornworms in your garden

You can discourage hornworms from invading your garden by clearing all nearby weeds. Many weeds serve as alternate hosts to tomato hornworms, including nightshade, horsenettle, jimsonweed, and many others. Tilling the soil after harvest is the best strategy that destroys all the pupae.

Crop rotation is another effective method for preventing tomato hornworms in your garden. Growing crops that don’t support hornworms can help reduce the load of pupae and egg-laying moths in your garden. Consider plants such as carrots, turnips, beets, broccoli, and cauliflower.

I have also tried companion planting and it has worked against tomato hornworms. Borage and Marigolds are my favorites as they also attract pollinators and other insects in tomato gardens. As you know, pollinating tomatoes is very essential for greater yield production.

Final thought

Tomato hornworms may occasionally feed on other plants but they are primarily a concern for crops in the Solanaceae family. They are dreaded for defoliating plants completely, resulting in massive losses. It’s always a good idea to monitor your garden regularly and take measures to control the caterpillars.