Identifying, Controlling, and Preventing the Tomato Hornworm

Is your tomato plant being mysteriously defoliated? A camouflaged caterpillar might be to blame!

Many gardeners encounter tomato hornworms, particularly in mid-to-late summer. These huge creepy-crawlies can eat and kill your tomatoes in no time!

Thankfully, preventing and controlling tomato hornworms is quick and simple. Learn how to identify the tomato hornworm and its damage, the difference between tomato and tobacco hornworms, and how to protect your plants from them!

Solanaceae Family Ties

The nightshade family (Solanaceae) encompasses a range of popular garden plants, including tomatoes, potatoes, eggplants, peppers, tomatillos, tobacco, and even goji berries. There are so many varieties to love, and I want to help you achieve gardening success and grow great tomatoes.

That’s why I have created resources to help you understand common tomato growing issues and their solutions. You don’t have to let blossom end rot, tomato leaves curling, tomatoes splitting, tomato plants dropping flowers, or pests get between you and amazing homegrown tomatoes!

Identifying Tomato Hornworms

The tomato hornworm can defoliate a plant overnight! And it is difficult to notice because it blends right in, perfectly camouflaged on your tomato plant.

The tomato hornworm (Manduca quinquemaculata) is a large green caterpillar that measures up to four inches long when fully developed. It has eight cream-colored V-shaped marks on each side and a mean-looking dark horn on its end.

It is often confused with the tobacco hornworm (Manduca sexta), which looks very similar except that (as you can see in the images above) it has seven thin, cream-colored diagonal stripes on each side and a red horn. Both types of hornworms love to feed on nightshades, like tomatoes.

Regardless of which type of hornworm you are dealing with, the prevention and control methods remain the same.

Tomato Hornworm Life Cycle

Tomato hornworms are the caterpillars of the beautiful five-spotted hawk moth. The pupae overwinter in the ground or in debris around the garden and emerge as adult moths in the spring.

When they emerge, adults feed on nectar. When they mate, the females lay their eggs on leaves by following the scent to a nightshade crop.

The caterpillars hatch and start feeding on the host plant for about four weeks… and they eat a ton! Tomato hornworms can double in size in a single day!

Mature caterpillars pupate and adult moths emerge two weeks later, starting the life cycle all over again. Although hawk moths do not pollinate food crops, they are still pollinators of some native and endangered plants.

Signs of Hornworm Damage

Examine your plants regularly and watch for these signs of hornworm damage:

• Defoliation - Look for missing leaves, especially the top branches. They will often be completely stripped of leaves. A hornworm can defoliate a plant in a short amount of time.

• Frass - On the ground around the defoliated plant, there will be little pellets of frass (insect poop). The greener the frass, the fresher. By the time the droppings turn black, the tomato hornworm has likely already moved on.

• Damaged Fruit - From time to time, they may even chew holes in fruit or stems.

If you find lots of frass and missing foliage, look near the base stem to see if they are hiding there, ready to pupate and turn into another moth.

Defeating The Tomato Hornworm: Prevention & Control Strategies

Many people think that hornworms are very beautiful and let them stay in their gardens. The choice is yours, but the risk is that they can decimate a garden in just a few days!

Use these prevention and control measures if you want to get rid of the tomato hornworm:

• Intercropping - When planting, try intercropping with other strong-smelling plants to mask the scent of your nightshades, so adult moths will not find them and lay eggs on them.

• Attract Birds - Encouraging birds to visit your garden with small bird feeders, birdhouses, and a birdbath is a great prevention strategy. Many types of birds, such as finches, blue jays, blackbirds, and cardinals, will seek out grubs, caterpillars, and larvae to eat, taking care of the hornworms before they ever become a problem.

• Release Beneficial Insects - Another effective tactic for preventing or eliminating hornworms is releasing beneficial insects, such as Trichogramma parasitic wasps, ladybugs, and green lacewings, which prey on the eggs and young caterpillars. Watch the video above to learn more about using the Trichogramma parasitic wasp in your garden.

• Remove Caterpillars - You can simply pick the tomato hornworms off the plants and exterminate them. If you feel squeamish about touching them, wear gardening gloves. This is often the only control method needed.

• Use Bacillus Thuringiensis (BT) - BT spray is an effective treatment for hornworms. This organic pesticide contains a bacterium that only affects chewing caterpillars when they ingest it, so it will not harm other beneficial pollinators, earthworms, birds, or people.