Tomato Hornworms: What Are They and How to Get Rid of Them
How to identify and control tomato hornworms using proven, natural and organic methods.
for Tomato Hornworms
Common throughout North America, the tomato hornworm (Manduca quinquemaculata) is one of the most destructive pests of tomato, potato, pepper, eggplant, and tobacco plants.
They consume entire leaves, small stems, and sometimes chew pieces from fruit. Despite their large size, hornworms are often difficult to spot because of their protective coloring.
Growers will often find large areas where feeding has occurred before they see this garden pest. Damage is most often noticed in midsummer and continues throughout the remainder of the growing season.
Whether you’re wondering how to spot them or get rid of them, this guide will tell you everything you need to know about tomato hornworms.
What are Tomato Hornworms?
The tomato hornworm is the larval stage of the five-spotted hawk moth, Manduca quinquemaculata. It is feared by vegetable gardeners because it can destroy tomatoes and other plants in the nightshade (Solanaceae) family.
Tomato plants, eggplant plants, pepper plants ranging from bell peppers to jalapenos and beyond, tobacco plants, and even potato plants can all serve as host plants for these pests.
Chew holes are often the first evidence of damage in the late spring, since the bugs feed there during their larval stage.
When they initially hatch, caterpillars are incredibly little and difficult to spot. Tomato hornworms can cause defoliation of plants as they continue to feed, leaving behind branches and veins of tomato leaves and nightshade plants that have been chewed on.
The adult form of the tomato hornworm is a relatively large, robust-bodied moth, commonly known as a hawk moth or sphinx moth. The adult moth feeds on the nectar of various flowers and, like the larval form, is most active from dusk until dawn.
How to Identify Tomato Hornworms
Likely to be the largest caterpillars you’ll see in the vegetable garden, tomato hornworms (3-4 inches long), are green with seven diagonal white strips and a black or red horn projecting from the rear.
The adults are large (4-5 inch wingspan), heavy-bodied insects with narrow front wings. They are mottled gray-brown with yellow spots on the sides of the abdomen and the hindwings have alternating light and dark bands.
Also called a sphinx moth, hawk moth, or hummingbird moth, they fly quickly and are able to hover like a hummingbird.
To find the larvae hidden among plants, look for black droppings (frass) on the leaves and ground and spray the foliage with water. The caterpillars will thrash about and give away their hiding spots.
The most active times for tomato hornworms are at dusk, dawn, and at night. They emerge to feed at this time, and while their camouflage makes it a little more difficult to notice them, they thrash and move, so you can use a flashlight during those times to try and spot them.
A UV flashlight is the best way to find tomato hornworms. When you shine a UV flashlight on these bugs, they glow, making your plant look like it has bulbs on it.
Also, look for stems that have lost part of their leaves and wilted leaves that are hanging down. You might see white cocoons and the hornworm hosts nearby.
Life Cycle of Tomato Hornworms
Overwintering occurs in the soil as dark brown pupae. Adult moths emerge in late spring, mate, and deposit spherical green eggs on the underside of leaves.
In 5 days hatching begins and the larva passes through five or six stages before reaching full growth in 3-4 weeks. These larvae eventually burrow into the soil where they transform into the pupal stage.
Adults develop in 2-4 weeks and work their way to the soil surface, where they mate and begin laying eggs for the next generation of hornworms. There are two generations per year.
Tomato vs Tobacco Hornworms
Often the tomato hornworm and the tobacco hornworm, Manduca sexta, are mistaken for one another. Both worms look quite similar and target members of the Solanaceae plant family.
The tomato hornworm is a 3 to 4-inch long, green caterpillar with eight diagonal white stripes down its sides and is likely to be the largest caterpillar you see in your garden. It has a black horn coming out of its back.
On the other hand, tobacco hornworms have seven white diagonal stripes and a red horn. The adult moth is known as the tobacco hawk moth or Carolina sphinx moth.
Damage Caused by Tomato Hornworms
Most gardeners will see signs of the tomato hornworm before finding the larval stage on their plants. It’s hard to spot the worms because they camouflage so well with the color of the plant. Also, the signs of these pests are similar to other pests.
Tomato hornworms leave large holes in your plant leaves and open spots where they’ve eaten all the plant matter. They weaken the plant by removing foliage, and sometimes even chew holes in fruits.
The adult moths often lay many eggs on a plant, and when several hornworms combine their feeding efforts, they can destroy so much foliage from the plant that the fruits become vulnerable to sunscald.
How to Get Rid of Tomato Hornworms
If you’ve identified a tomato hornworm problem in your yard, don’t worry. Here’s what you can do to get rid of them:
Handpick Hornworms Off Your Plants
Because they are so large hornworms are most often controlled in home gardens by handpicking. Once removed from the plant, they can be destroyed by dropping them into a bucket of soapy water.
Introduce Beneficial Insects and Natural Predators
Beneficial insects including green lacewings, braconid wasps, trichogramma wasps, and ladybugs attack the eggs. For best results, make releases when pest levels are low to medium.
Try a Natural Pesticide
If populations are high, use a least-toxic, short-lived natural pesticide to establish control, then release predatory insects to maintain control.
If pest levels become intolerable, you can also spot treat with a fast-acting organic insecticide. For best results, apply to the undersides of leaves and deep into the plant canopy where insects hide.
Use Bt (Bacillus thuringiensis)
Apply Diatomaceous Earth
Apply 100% organic Diatomaceous Earth for long-lasting protection. Made up of tiny fossilized aquatic organisms, that look like broken glass under the microscope, DE kills by scoring an insect’s outer layer as it crawls over the fine powder. Contains NO toxic poisons!
Till the Soil
Roto-tilling after harvest destroys overwintering pupae in the soil. This is especially effective since pupae are large and not buried very deeply in the soil. Results have shown that greater than 90% mortality is caused by normal garden tilling.
Crop rotation is another natural method for reducing or eliminating hornworms in the garden. It works to lessen the number of pupae that will eventually develop into egg-laying moths in the soil and can be a great way to help get rid of them as well.
Use Companion Planting
To get rid of tomato hornworms naturally, consider companion planting. Basil grown close to your tomatoes enhances their flavor while also keeping hornworms away from these plants.
Borage is a similar companion plant that successfully works to reduce hornworms. Pollinators and beneficial insects will be drawn to your garden if you plant borage.
You can also use parsley, dill, mustard, or marigolds as companion plants to help get rid of tomato hornworms in your garden.
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