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Tomato Horn Worm

Updated on February 16, 2013
seh1101 profile image

Sean has been in the industry of gardening and landscaping since 2006. He is also a certified arborist that tends to focus on plant health.

A hornworm on a tomato plant leaf.
A hornworm on a tomato plant leaf. | Source

Tomato hornworms are known to eat various plants, commonly munching on tomato, eggplant, pepper, moonflowers, and potato. Hornworms are often found underneath leaves of defoliated plants. The caterpillars are difficult to spot due to their green coloration.

The hornworm is the larval stage of a five-spotted hawkmoth. The caterpillars can be found during the summer before becoming pupae. The pupae remain in the soil until spring and emerge as moths to reproduce.

The hornworm can become a major problem in gardens, but there are several methods of defense when dealing with the destructive caterpillars. There are a few organic and chemical methods of control that can be used. Each method provides different but effective results.

Hornworm eating tomato
Hornworm eating tomato | Source

What are Tomato Hornworms?

Larval Stage
The tomato hornworm (Manduca quinquemaculata) is the larval stage of the five-spotted hawkmoth. The caterpillars can become major nuisances in gardens due to their ability to strip plants of foliage. The caterpillars are green to light green with V-shaped markings on the body. The end of the caterpillar features a small, yellow horn-like appendage.

Pupal and Adult Stages
Moths will emerge from pupae in the summer months. The moths mate and then deposit eggs that hatch in late summer. The caterpillars fill up on foliage before becoming pupae. The pupae remain in the soil through autumn and winter. Moths emerge from pupae the following summer and begin reproduction.

Tomato Hornworm Damage

Hornworms can completely defoliate a plant relatively quickly. Chew marks and caterpillar droppings can be found fairly easily on the leaves. The fruits may also be eaten or stunted by the caterpillars. Most damage usually occurs under the canopy which can make damage difficult to notice at first. Stems may also be consumed by mature caterpillars. Young fruit are targeted more often by hornworms compared to mature fruit.

Parasitic wasps are biological controls of hormworms.
Parasitic wasps are biological controls of hormworms. | Source

Tomato Hornworm Control

Control Applications
The simplest way to control hornworms is to pick them off of plants by hand and destroy them. The hormworm can also be eradicated by others means. Foliage insecticidal spray is usually the first that comes to mind amongst most people. Insecticidal soap can be mixed and sprayed directly onto the worms. Soaps interfere with the worm’s ability to respirate and follow a more organic route. Neem oil follows the same route, but causes the foliage to become undesirable to the hornworm.

Biological Control
Bacillus thuringiensis (Bt) is a bacteria and a biological pesticide. This method is ingenious when observed at the micro scale. Bacillus thuringiensis (Bt) is a type of bacteria that naturally dwells in soil. The brilliant aspect of certain Bt strains occurs during reproduction. Bt reproduction results in spores. Bt releases crystal proteins during sporulation called "endotoxins." The endotoxins are destructive to caterpillar digestive systems, especially the digestive system of hornworms. Bt has been used since the 1920s, and is renown for being environmentally safe. Humans, animals, beneficial insects, and other plants are unaffected by Bt.

A family of parasitic wasps, Braconidae, target hornworms and are a great example of a biological control. The wasps lay tiny sac structures on the body of the caterpillar. The parasitoids grow by the help of a virus that suppresses the immunity and mobility of the hornworm. Eventually the hornworm dies from the parasitoids. Do not eradicate hormworms with Braconidae parasitoids. The parasitoids will mature into wasps and seek out other hornworms that are stripping plants of vegetation.

Predatory insects such as lady beetles and green lacewings often prey upon the eggs of the five-spotted hawkmoth.


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    • moonlake profile image

      moonlake 5 years ago from America

      I have seen a few of these. I never do anything with them. I guess I just don't get that many. Interesting hub. Voted uP!

    • jimmythejock profile image

      James Paterson 5 years ago from Scotland

      Luckily we don't have them in the UK and our tomatoes are safe from them lol.....jimmy

    • seh1101 profile image

      Sean Hemmer 5 years ago from Wisconsin, USA

      gmarquardt - Thank you much! I usually have a few too many tomato plants so a few caterpillars don't seem to harm anything. The adult moths are pretty neat.

      Peggy W - Thanks! I let the caterpillars do as they please since my tomato plants usually end up growing out of control, but I take it personal if they start to completely shred my plants ;)

    • Peggy W profile image

      Peggy Woods 5 years ago from Houston, Texas

      Like gmarquardt, I personally dislike killing things. Often, I just move them to the front yard where I do not have plants that they like to eat. I have had tomato and parsley plants just about defoliated before I discovered the hungry culprits. Up votes and tweeting.

    • gmarquardt profile image

      gmarquardt 5 years ago from Hill Country, Texas

      We get plenty of tomato hornworms here in Texas. We just toss them over the fence and let them go, they usually don't come back. However, if we are gone for a long weekend, the entire top of one or more plants might be gone! Well written, up and shared!