How to Get Rid of Tomato Hornworms on Tomato Plants

Disclosure: The links in this post may be affiliate links. If you purchase any products after clicking on these links, at no additional cost to you, Seeds for Generations may receive a small commission for making you aware of these important resources.

Tomatoes are one of the most common crops grown gardens around the world, but they also can attract one particularly menacing pest, the tomato hornworm! Recognizable by its fat green appearance and voracious appetite, this caterpillar can wreak havoc on tomato crops and other plants in a short amount of time.

In this article, we will delve into the world of tomato hornworms, exploring their identification, life cycle, and effective methods for controlling these destructive worms without chemicals.

What are Tomato Hornworms?

Hornworms, scientifically known as Manduca quinquemaculata, are a species of caterpillar belonging to the Sphingidae family. These insects are characterized by a distinct horn-like projection on their posterior, which gives them their name. While there are different types of hornworms, the tomato hornworm (M. quinquemaculata) is a significant pest in agricultural settings. Tomato hornworms primarily feed on the foliage of tomato plants but may also target other plants such as peppers and eggplants and eat the tomato fruit too. It is crucial to identify their presence early to prevent significant destruction.

How to Identify Tomato Hornworms

Tomato hornworms have a green coloration with white diagonal lines on the body and prominent legs. You will notice a horn-like protrusion on the posterior end. Don’t worry–they don’t actually sting. The “horns” on tomato hornworms are actually not horns but rather protrusions that resemble horns. These structures, known as “false eyes,” are located on the posterior end of the caterpillar and serve as a defensive mechanism to deter predators. They can startle or confuse predators by making the caterpillar appear larger or more threatening than it actually is.

At approximately 3-4 inches in length, you’d think tomato hornworms might be highly visible on tomato plants, but they have amazing camouflage that makes them blend in with the surrounding vegetation. They are most active during the early morning and late evening, making those times ideal for manual removal.

While tomato hornworms are the most common caterpillars found on tomato plants, other species of worms may be found on tomato plants too, including:

1. Tobacco hornworms: Similar in appearance to tomato hornworms, but with dark diagonal lines instead of white. The horn of a tomato hornworm is reddish, whereas that of a tobacco hornworm is black, and tomato hornworms primarily target tomato plants, while tobacco hornworms prefer tobacco and related plants.
2. Armyworms: Gray or green with a series of stripes along the length of their bodies.
3. Cutworms: Gray-brown caterpillars that hide in the soil during the day.

Visual Signs of Tomato Hornworm Infestation 

First, the caterpillars have a hearty appetite, capable of devouring large sections of leaves. This leads to complete defoliation of certain branches or even the entire plant, negatively impacting its overall health. You will notice chewed stems with worms leaving behind ragged, irregularly-shaped holes. These injuries weaken the plant’s structure and can stunt its growth.

While primarily vegetative feeders, tomato hornworms do sometimes attack the ripe or green fruit too, leaving behind visible holes or gouges. If the infestation is severe, the caterpillars can completely consume large sections of the fruit, causing it to rot prematurely.

When it comes to timing, tomato hornworms are most active during the late summer months, typically peaking in August and September. They go through several developmental stages. At the most destructive stage, the caterpillars are fully grown, measuring about 4 inches in length and are consistently voracious feeders.

Tomato hornworms tend to feed mainly during the night or in lower light conditions, making them even trickier to spot during daytime inspections. Although they can eat at any time, they are less active during the hot, midday hours, as they prefer cooler temperatures.

Photo Credit: Didier Descouens CC 4.0 

The Life Cycle of the Tomato Hornworm

The life cycle of a tomato hornworm involves several stages:

1. Eggs: Female moths lay small, greenish eggs on the underside of tomato leaves or other host plants. Eggs hatch in about 3-7 days.
2. Larvae: After hatching, the larvae feed voraciously on the foliage of tomato plants and grow rapidly. The larvae remain caterpillars for about 2-4 weeks total.
3. Pupae: When fully grown, the caterpillar burrows into the soil to form a pupa or cocoon.
4. Adult Moths: The hawk moth emerges from the pupa about 2 weeks after burrowing and embarks on finding mates to continue the cycle, laying eggs for another 2 weeks. 

What Do Tomato Hornworms Turn Into?

Tomato hornworms undergo a fascinating metamorphosis, ultimately transforming into an adult moth. The adult form of the tomato hornworm is known as the hawk moth or sphinx moth. This transformation occurs during the pupal stage, which takes place in the soil.

A female hawk moth can lay up to 200 eggs, contributing to rapid infestations! These moths are characterized by their rapid, hovering flight and their ability to drink nectar from flowers using their proboscis. They are essential pollinators for various plant species.

Organic Ways to Get Rid of Tomato Hornworms in the Garden 

Picking Off Tomato Worms By Hand

One straightforward and immediate method to control tomato hornworms is handpicking. Keep an eye on your plants for worms, especially focusing on the undersides of leaves and new growth where caterpillars might hide. When you find hornworms, carefully remove them by hand and drop them in a bucket of soapy water or feed to your chickens. (Chickens LOVE them!)

Best Organic Pesticides & Sprays for Tomato Hornworms

One effective organic spray for eliminating tomato hornworms is Bacillus thuringiensis (Bt). Bt is a naturally occurring soil bacteria that produces toxins harmful to worms, including tomato hornworms. Mix the recommended amount with water and spray it on your plants thoroughly. Bt specifically targets caterpillars and is harmless to beneficial insects, animals, and humans.

You can also use neem oil in a spray for tomato hornworms. Neem oil contains compounds that interfere with their hormonal system, impacting feeding, mating, and egg-laying. It also is known to suffocate and kill worms upon contact. 

Diatomaceous Earth for Tomato Worms

Diatomaceous Earth (DE) is a fine powder made from fossilized remains of tiny aquatic organisms. Sprinkling DE on the leaves of your tomato plants can then irritate and dehydrate the hornworms. Reapply after rain or watering.

Companion Planting & Crop Rotation for Deterring Tomato Worms

Companion planting is an effective and natural way to repel tomato hornworms. Planting herbs like basil, dill, or mint near your tomato plants can deter these pests. Certain flowers, such as marigolds and petunias, can also be effective in repelling hornworms. Their strong scents help confuse and repel the pests.

In addition, regularly rotating corps can help disrupt the lifecycle of hornworms and reduce the likelihood of future infestations.

Natural Predators of Tomato Hornworms

Nature provides an army of beneficial insects and animals that feed on tomato hornworms. For instance, young parasitic wasps are one of the most important natural predators. These wasps lay their eggs under the skin of the hornworm. Once the eggs hatch, the wasp larvae feed on the hornworm, eventually killing it. The hornworm’s body is then used as a protective cocoon for the wasp larvae to complete their development.

Parasitic wasp eggs on tomato hornworms appear as small, white, rice-like structures attached to the body of the caterpillar. Make sure to move them instead of destroying them!

In addition, ladybugs, lacewings, and birds, such as the Carolina Wren, also feed on hornworms. Encourage their presence in your garden by providing suitable habitats.

Conclusion: How to Get Rid of Tomato Hornworms

Tomato hornworms can be a nuisance for tomato growers, but understanding their lifecycles and adopting organic methods can effectively control their population and prevent damage to your plants. You can beat these tomato hornworms and reclaim your tomatoes from this feisty garden pest!