Hornworms

Just For Fun

You may be familiar with these mean looking creatures. Tomato hornworms look menacing, but the real damage that they do is in your garden. Let’s talk about what they look like and what you can do about them in the garden.

The tomato hornworm doesn’t only feed on tomatoes; they will eat anything in the solanaceae plant family. This includes tomatoes, eggplant, peppers, and potatoes. They will grow and go into their cocoon phase to emerge as a type of sphinx moth. Tomato hornworms have v-shaped yellow lines that run the length of their body. They have small brownish dots that look like eyes running the length of their body too. There is a black protrusion on the end of their body that looks like a stinger. This is to scare predators away and can’t actually hurt you. There is another hornworm called the tobacco hornworm that looks very similar to the tomato hornworm. The main difference is the tobacco hornworm just have diagonal white lines instead of a V-shape on its body. The horn on the tobacco hornworm is more reddish. Both can cause a lot of damage in your garden, and are controlled the same way.

The older and larger hornworms get the more damage they do, until they turn into moths. They start out pretty small at about half an inch long. At this size, they won’t do a lot of damage to plants. However, they grow quickly, and within four weeks are full-grown and up to 4 inches long. A 4-inch long hornworm can cause some serious damage very quickly, especially if you have a lot of them. They can rapidly defoliate entire plants. Because of their green body, they blend in with the plants, so you might not notice them until they have done significant damage. They will also leave behind dark green or black droppings that you might be able to see.

Managing hornworms is not difficult if you are walking through and closely looking at your plants a couple of times a week. Handpicking them and putting them in a container of soapy water usually works pretty well. If a jar of soapy water isn’t handy, you can also sling them onto the ground. A sight that you might see is a hornworm with lots of small white egg sacks attached to its back. These are from a parasitoid wasp. The eggs will hatch and the larvae will eat the hornworm from the inside out. Ladybugs and lacewings also serve as predators of hornworm eggs and young caterpillars. There are a couple of insecticides that you can use. It’s best to use insecticides on hornworms before they are full grown, because insecticides won’t be as effective against a 4-inch caterpillar. Bt is an organic insecticide that is effective against caterpillars. Spinosad is an insecticide that is derived from natural microorganisms that also works well. Permethrin will also work well to control many different types of pests on vegetables. Always read and follow the label for any insecticide that you use, whether it is organic or synthetic. 

If you have questions about hornworms or other garden pests contact your County Extension office or email me at [email protected].

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