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Tomato Hornworms: Wiping Out Manduca Quinquemaculata

Anyone who’s as much a fan of home-grown tomatoes as I am is terrified of this fat green tomato worm, and for good reason. Tomato hornworms can destroy tomato plants in rapid-fire fashion. But there’s still hope! With some preparation and careful management, you can get rid of this garden pest and keep it from coming back.

Organic Control Options:

Environmental Control Options:

To Prevent Tomato Hornworms, Use:

Tomato Hornworm Overview

Common Name(s) Tomato hornworm, five-spotted hawkmoth
Scientific Name(s) Manduca quinquemaculata
Family Sphingidae
Origin United States, northwestern Mexico, and parts of southern Canada
Plants Affected Solanaceae family plants such as tomatoes, potatoes, eggplant, pepper, tobacco, moonflower.
Common Remedies BT sprays and dusts, pyrethrin sprays, spinosad sprays, floating row covers, parasitic wasps, ladybugs, lacewings, diatomaceous earth

We all know that the tomato hornworm is a legendary destroyer of home vegetable gardens, and people have good reason to dread their appearance. But how can you identify them, and how do they spread throughout your garden? Let’s examine the hornworm life cycle from start to finish, talk about the differences between the tomato hornworm and the tobacco hornworm, and discuss what kinds of plants they eat.

What Do Tomato Hornworms Look Like?

Tomato Hornworm Life Cycle
Source: TexasEagle

Tomato hornworms are some of the biggest caterpillars you’re likely to find in your garden. On average, these tomato worms are three to four inches in length. They are bright green with around seven diagonal V-shapes along their sides. A black tail-like horn protrudes from the rear. A close relative, the tobacco hornworm, has a red-colored horn and diagonal white stripes instead of V-shapes but is otherwise identical. Both tomato and tobacco hornworms prey on similar plants, so it’s quite possible to misidentify one as the other since they do the same types of damage.

In addition, both types of hornworms have breathing holes along their sides that are called spiracles. These look like little yellow-and-black spots near the white V’s or stripes.

As an adult moth, the five-spotted hawkmoth is huge, often reaching wingspans of 4-5 inches. On the abdomen of the adult moth, there are five spots, hence the name. These moths look a bit fuzzy, and are otherwise a greyish-brown in color.

Tomato Hornworm Life Cycle

Tomato hornworm larvae
Source: foxtail_1

The tomato worm life cycle begins as overwintering adults emerge in the late spring. These tomato worms then mate and lay eggs on the underside of leaves. The tomato hornworm eggs are spherical and are whitish to light green in color.

Within about five days (although it can be as quickly as two days and as long as seven), tomato hornworm larvae emerge from their eggs. These larvae go through five or six stages of growth, shedding their skin and becoming larger over the course of 3-4 weeks time. This period is when a tomato caterpillar is at its most destructive, and when it can decimate the plants that it’s living on and around.

Once the larval stages have concluded, the final form of the larva will burrow into the ground and pupate. They form a pupa around themselves for protection under the soil’s surface. The pupal stage can take 2-4 weeks to conclude, after which the adult tomato hornworm moth will dig its way to the surface and emerge to start another generation.

In most areas, there are two full lifecycles per year. Some particularly warm regions may have a third lifecycle over the winter months, but generally the hornworms will burrow into the soil to pupate and effectively hibernate in their pupa over the winter in a kind of suspended animation.

Common Habitats For Tomato Hornworms

The tomato hornworm can be found throughout the United States, Mexico, and even southern Canada. They are less common in some regions of the southeastern United States and in the Great Plains region than in other areas.

Tomato hornworms prefer to live around large populations of Solanaceae-family plants, such as tomatoes, potatoes, eggplants, and nightshades. These plants provide an ideal habitat for them due to their large leafy structure, which is ideal for egg-laying and food purposes.

What Do Tomato Hornworms Eat?

Not only do tomato worms eat tomatoes, but they also consume tobacco, potatoes, eggplants, some pepper plants, other nightshade-family plants, and moonflowers. One larva can decimate a plant very rapidly, as they have voracious diets. Further, the coloration of the larva acts as camouflage, making it difficult to see the larvae despite their significant size. It’s generally easiest to identify the damage that they do, which includes devouring whole leaves and smaller stems on the plant, and occasionally leaving holes in the side of fruit. You can also see their waste on leaves as a blackish dropping.

How To Get Rid Of Tomato Hornworms

Manduca quinquemaculatus
Manduca quinquemaculatus, the adult moth form of the tomato hornworm. Source: David Bygoth

If you think you’ve found signs of tomato hornworms, spray the plant with some water. The hornworms will thrash around and give away their position, making them relatively easy to pick off by hand.

But what if there’s just too many, or you’re sure you’ve missed some? Maybe your tomato trellis is making it difficult to find them, or your plants are just too bushy to easily search through? Let’s go over some alternatives that you can use to combat this pest.

Organic Tomato Hornworm Control

If you’re looking for a way to effectively go about killing tomato worm without harming other beneficial insects or normal garden worms, consider Monterey BT spray. BT, which is short for Bacillus thuringiensis var. Kurstaki, is a naturally-occurring bacteria that will poison all manner of caterpillars, including tomato hornworm, cabbage worms, cabbage loopers, cutworms, and many other types of larvae.

If you would prefer not to use a spray but still want to use BT Kurstaki to kill tomato hornworms, you might consider Garden Dust. Garden dust is a powdered form of Bacillus thuringiensis var. Kurstaki, and when it is dusted to coat the surface of plants, it works just as effectively as the spray form does.

If you are looking for an alternative choice in how to kill tomato worms, consider pyrethrin sprays. There are many variations on these on the marketplace today, including powerful pyrethrin-only options such as PyGanic. There are also blended formulas that combine pyrethrin with other insecticides, such as Safer Brand Home And Garden Spray.

Spinosad-based sprays such as Monterey Garden Insect Spray can also be an effective way to kill tomato hornworms before they can devour your plants. Monterey also produces a tomato & vegetable spray, but it has an identical spinosad formulation as their catch-all garden insect spray.

Environmental Tomato Hornworm Control

For this pest, environmental controls are absolutely key to ensuring your survival. And one of the best options is the use of beneficial insects.

Beneficial predatory wasps are a major form of tomato hornworm control. These wasps will lay their eggs inside or on top of the hornworm, and when the wasp larva hatch, they will devour the hornworm. Trichogramma wasps are the most commonly available predatory wasps, and while they won’t harm humans or pets in any way, they love to eat garden pests!

Lacewings and ladybugs are also really useful when trying to kill tomato hornworms, because they happily eat the eggs that are on the bottom of leaves. While you still need to remove already-hatched larvae by hand, you can reduce future generations that might hatch with these two friendly beneficial insects.

Companion planting can be beneficial in the fight against tomato hornworms, especially around tomatoes. Planting basil nearby will improve the flavor of your tomatoes while simultaneously repelling tomato hornworms, flies, mosquitos, and some other moths. Similarly, borage will attract bees and other beneficial insects while repelling tomato worms. Finally, marigold is a wonderful draw for all manner of beneficial insects, including parasitic wasps, and its aroma tends to repel or confuse most caterpillar species so they don’t move in.

Preventing Tomato Hornworms

One of the most effective means of tomato hornworm control is simply not allowing the five-spotted hawkmoth to reach your plants in the first place. To do that, use floating row covers over your plants until they need to be removed for pollination.

Once you have removed the floating row covers, you can use diatomaceous earth sprinkled on the leaves and stems of your plants as a repellent measure. Diatomaceous earth is harmless to humans and pets, but to all forms of caterpillars, it’s sharp and will cut up their tender bodies. It can also cause hornworms to dehydrate and die if they are sliced up often enough.

Tilling your garden at the end of the harvest season can help reduce future hornworm populations. Tilling will dig up any overwintering insect populations that might be lingering in your garden beds, leaving them exposed for birds to eat or other insects to devour. Till again in the early spring before planting to make sure you got them all.

When Should You Avoid Killing Tomato Hornworms?

If you see a tomato hornworm that looks like this...leave it be! It's being attacked by a parasitic wasp, and will produce more wasps!
If you see a tomato hornworm that looks like this…leave it be! It’s being attacked by a parasitic wasp,
and will produce more wasps! Source: Waldo JaquithX

Have you ever seen a tomato hornworm that looks like it’s developed a series of whitish spikes on its back? If so, leave that one alone! That tomato worm is now a hatching ground for braconid wasps, another form of parasitic wasp that lays its eggs on the exterior of caterpillars. When those wasp eggs hatch, the larvae will devour the hornworm from the inside out, and then will grow to become adult predatory wasps to help keep the rest of your garden caterpillar-free.

Unfortunately, there’s a cost for allowing a braconid wasp colony to develop from egg to adult in your garden. That colonized hornworm is going to keep eating until the wasp larvae hatch, and that means you will lose some more greenery on your potatoes or tomatoes, peppers or eggplants. But the damage caused by one colonized hornworm is a small price to bear to have these wonderful beneficial insects in your yard.

If you’d like to encourage the braconid wasps to stick around in the future, grow plants like mustard, dill, yarrow or parsley, as the adult wasps feed on nectar from these plants. Marigold is another great choice to encourage beneficial wasps to move in.

Frequently Asked Questions

Q: Are tomato hornworms harmful to humans?

A: They’re big, and they look a bit intimidating to pull off the plant, and they occasionally make a menacing-sounding clicking noise… but they can’t hurt you. As gross as they are, they’re really quite harmless to us. In fact, they’re so non-harmful to us that there are actually recipes online for ways to cook and eat tomato hornworm. It reputedly tastes tomato-ish, but I wouldn’t know, as I try to avoid eating my garden pests!

Q: I can’t get the tomato hornworm off my plant!

A: They are tenacious little critters, aren’t they? Many people have found it difficult to grab that 3-4″ long worm and tug it free, because it hangs on for dear life. However, there’s another option if you’re not squeamish. Take a pair of long-bladed scissors and cut the hornworm in half. It will die and fall off the plant, making it easy to dispose of.

So, there you have it, everything you need to know to get the tomato hornworms (or even tobacco hornworms) out of your garden! Have you ever waged war against these ravenous little caterpillars in the past? What’s the biggest hornworm you’ve ever seen? Share your stories in the comments!

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