Today we are going to take a quick look at the big ugly tomato hornworm. Many times, they seem to appear and demolish big chunks of your tomato plants almost overnight. Fortunately, they are easy to manage, and they do not require any pesticide usage to control. If you are unfamiliar with this garden pest, read on to learn how to spot and control tomato hornworms in your garden.
How to spot tomato hornworms
The first thing you typically see is not the worm itself. These caterpillars do a remarkably good job of camouflaging themselves. The first sign you often notice is that there are big bald patches on your tomato plants. There will be stems with all the leaves stripped, and you might also notice green fruit eaten. This damage is usually accompanied by large green or black poop pellets all over the ground.
If you see damage on your plants like this and do a thorough inspection in the areas around where the feeding damage has occurred, you will likely find one or many tomato hornworms. Just like other caterpillars they start as eggs that hatch into small worms that usually go unnoticed until they get large. The appetite of the large worms is incredible resulting in noticeable damage. Left unchecked they can completely defoliate your tomato plants. Though tomato plants are their preferred host, they may also be found munching on other nightshade family plants like eggplants peppers and potatoes.
Tomato hornworms are very distinct and easy to recognize. They are a large green caterpillar up to 4” long. The younger larval phases are less obvious and usually missed. These caterpillars are a yellowish white with no markings on them. The large caterpillars are bright green and have white markings on their sides. They have a large horn on their last abdominal segment giving them their name hornworms.
Tomato hornworm lifecycle
Just like most insects they go through the egg, larvae (caterpillar), pupae and adult moth phases. Moths lay eggs on your tomato plants. These eggs hatch out into the caterpillars that eat your plants. When, the caterpillars are full grown, they pupate. They drop off and bury themselves in the soil. These pupae can hatch and produce a second generation or they may sit dormant into the soil until the following spring.
After the eggs hatch it takes 3-4 weeks for the caterpillars to reach full grown when they drop off the plants to pupate. About 2 weeks after that the second generation moths can hatch to repeat the cycle producing overwintering pupae. You likely won’t see the moths, but they are large grey moths with whitish markings.
Though tomato hornworms can do an impressive amount of damage very quickly, they are easy to control.
For most home gardeners picking the worms off and squishing them provides adequate control. You should make it a habit of checking your plants for hornworms at least a couple times a week during the summer. You will have to look at your plants carefully as the worms can be tricky to spot.
You likely will not notice them until some of the worms get large and defoliate a portion of your plant. If this happens don’t be alarmed. Just thoroughly check your plants for worms every day for a while to prevent more damage. Tomato plants are usually vigorous enough to tolerate some feeding damage without it harming them.
Something else you can do to help control tomato hornworms is till up your soil in the fall. This can help to kill pupae overwintering in the soil. It’s a particularly good idea to do this if you have high hornworm pressure or you think that you missed picking some of the worms off the plant and thus allowed them to pupate.
Lastly, we would like to note that tomato hornworms have a variety of natural predators.
Some predatory insects like ladybugs will eat eggs and young caterpillars. Thus, predatory insects should always be encouraged in your gardens.
Perhaps one of the most interesting predators of tomato hornworms is a type of parasitic wasp, the braconid wasp. This particular wasp lays eggs on the hornworms. When the larvae hatch, they feed off the worm until the wasp larvae is ready to pupate. When the wasps pupate they do so in small cocoons hanging off the hornworm.
If you see a hornworm with little rice like pupae hanging off of it, leave it be. Yes, it looks gross, but that hornworm is dead and not harming your plant any more. Plus, the predatory wasps will hatch from the pupae and go in search of more tomato hornworms to parasitize. By leaving predatory insects such as this alone, you can help nature help you.
We hope this helps you to succeed with your garden this summer. If you would like to read more articles about pests you might encounter in your garden, don’t forget to sign up for our newsletter!
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