Few garden pests inspire more dread than the tomato hornworm. These mega caterpillars can quickly shred your prize tomatoes to leafless stalks before you even realize they’ve arrived.
But don’t panic – understanding these voracious eaters is the first step to effective control.
1. They’re Not Actually Worms
Tomato hornworms are not worms at all. They are the larval stage of the five-spotted hawkmoth (Manduca quinquemaculata). These large caterpillars can grow up to 4 inches long and are easily recognizable by their bright green color, white V-shaped markings, and distinctive horn-like tail.
These little caterpillars have a massive appetite. A single hornworm can consume up to four times its weight in leaves and fruit daily. Left unchecked, a few hornworms can quickly strip a tomato plant bare.
2. They Have a Specific Taste for Nightshades
Tomato hornworms have a particular affinity for plants in the nightshade (Solanaceae) family. While they are most commonly found on tomato plants, they will also happily munch on peppers, eggplants, potatoes, and even tobacco
If you grow any of these crops, it’s essential to keep a watchful eye out for hornworms.
3. They Have a Fascinating Life Cycle
The life cycle of the tomato hornworm consists of four distinct stages: egg, larva (caterpillar), pupa, and adult moth.
- Female moths lay small, spherical eggs on the undersides of leaves in late spring or early summer.
- The eggs hatch in about a week, and the tiny caterpillars immediately begin feeding voraciously.
- Over the next 3-4 weeks, the caterpillars molt five times, growing larger with each instar.
- The caterpillars burrow into the soil to pupate once fully grown. They emerge as adult moths in 2-3 weeks
.Targeting the caterpillars when they are small and before they have caused significant damage is key.
4. Early Signs of Infestation Can Be Spotted
Because of their impressive camouflage and mind-boggling growth rate, tomato hornworm infestations often aren’t discovered until significant foliar damage has already occurred. The earliest indications are:
- Large black or green droppings (called frass) accumulating on leaves and soil
- Plant leaves and stems becoming skeletonized, with only veins remaining
- Holes chewed into fruits and vegetables
But by the time these calling cards show up, the mega hornworms themselves won’t be too far behind, hungrily devouring leaves and fruit in their paths.
5. Handpicking is an Effective Control Method
One of the simplest and most effective ways to control tomato hornworms is to remove them by hand. Hornworms are relatively big compared to other pests, so they’re easy to spot and pluck off your plants.
When handpicking, be sure to check the undersides of leaves and inside the plant canopy, as hornworms often hide during the day. Dispose of the caterpillars by dropping them into a bucket of soapy water or feeding them to your chickens.
6. Beneficial Insects Can Help
Nature has its own way of keeping tomato hornworms in check through beneficial insects. Several predatory and parasitic insects target hornworms at various stages of their life cycle.
- Ladybugs and green lacewings prey on hornworm eggs and small caterpillars.
- Braconid wasps lay their eggs inside the bodies of hornworms. The wasp larvae then feed on the caterpillar from the inside out.
- Paper wasps feed on early instar hornworm larvae.
Encouraging these beneficial insects in your garden can help maintain a natural balance and reduce hornworm populations. Avoid using broad-spectrum insecticides that may harm these helpful predators.
7. Neem Oil: A Safe & Effective Insecticide
Neem oil, derived from the seeds of the neem tree, is a natural insecticide that can effectively control tomato hornworms. (ref) It works by disrupting the hormonal balance of the caterpillars, preventing them from molting and reaching adulthood.
To use neem oil, mix it with water according to the manufacturer’s instructions and spray it on your tomato plants, ensuring thorough coverage of both the upper and lower leaf surfaces. Reapply every 7-10 days, or after heavy rain, for best results.
8. Tilling the Soil Can Disrupt Their Life Cycle
Tomato hornworms overwinter as pupae in the soil, emerging as adult moths in the spring to begin the next generation. Tilling your garden in the fall or early spring can help disrupt this cycle.
Turning the soil exposes the pupae to the elements and predators, significantly reducing the number of adult moths that emerge. A study from Utah State University have shown that tilling can cause up to 90% mortality in overwintering hornworm pupae. (ref)
9. Companion Planting: A Natural Deterrent
Companion planting is a technique that involves growing specific plants together to benefit each other. Some plants can act as natural deterrents for tomato hornworms, making your garden less appealing to these pests.
Consider planting the following companions around your tomatoes:
- Basil
- Marigolds
- Dill
- Borage
These plants emit scents that can confuse or repel hornworms, reducing the likelihood of an infestation.
10. Best Defense is a Healthy Garden Ecosystem
Ultimately, the best defense against tomato hornworms is a healthy, diverse garden ecosystem.
Some key practices to maintain a healthy garden include:
- Providing habitat for beneficial insects (e.g., planting flowers that attract pollinators)
- Avoiding the use of broad-spectrum pesticides, which can harm beneficial insects
- Properly spacing and pruning your tomato plants to promote good air circulation and reduce pest pressure
- Keeping your garden clean and free of debris, which can harbor pests
As they’ve said, the best defense (against tomato hornworms) is a good offense. Regularly monitoring your plants for signs of damage and promptly removing any caterpillars you find can prevent a small problem from becoming a major infestation.
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Davin is a jack-of-all-trades but has professional training and experience in various home and garden subjects. He leans on other experts when needed and edits and fact-checks all articles.