They are ugly, and look like something right out of a Harry Potter novel. And they can devour a tomato or pepper plant faster than you can say, “Hogwarts School of Witchcraft and Wizardry.” They also have been known to chomp on eggplant too. Tomato Hornworms, also known as Tobacco Hornworms, are the larva of a giant mouth called the Five Spotted Hawkmoth. About the size of a hummingbird, this moth is brown in color with yellow spots on the side of their body. In fact, some people do call it a hummingbird moth.
The moths lay their eggs on the underside of the plant leaves. They come around about now, and the eggs hatch in about a week. They spend close to a month feeding. They have an appetite like a cormorant and can quickly consume the leaves and stems of tomato and pepper plants. there can easily be two generations of them and if you are not vigilant, you can kiss your prized tomato crop goodbye. When they have gorged themselves on your crop, they drop to the ground and dig themselves into the soil. They hatch in the spring as a fully grown moth.
You can keep them under control several ways. If you have just a few plants, it’s best to just scout them out on your morning walk through. They’re hard to see, their green color blending in very well with the plant’s leaves. I pluck them off by hand, but if you’re a bit squeamish about doing that, carry a pair of long nosed pliers and grab them with those.
Ladybugs like the eggs, and so do Green Lacewings. If you see one of these things covered with little white spots, leave it alone. It’s undergoing a slow death, being eaten by the larva of the small Braconid Wasp. This little gal lays her eggs on the worm, which then feed on the worm until they are ready to pupate. Some advocate picking off the infected worm and putting it in a jar, allowing the wasps to enjoy their feast. I personally don’t feel this is necessary. Another wasp, Polistes, kills and eats the worm whole.
Commercial tomato growers don’t get excited about the hornworm until the ratio gets to 0.5 larvae per plant. Once this level is reached, insecticide treatment begins, usually with BT (Bacillus thuringiennsis).
Another effective method at controlling the pupa stage is by thoroughly tilling both in the fall and spring. The deeper the better. I don’t recommend deep tilling for the whole garden, just where plants that are susceptible to this pest.
Those who treat their tomatoes to containers do not seem to have this problem as much. But the secret there is to not use soil from your own garden; rather potting soil that has been “sanitized” by having been heated to kill all the nasty stuff as well as a good portion of the embedded weed seed.
Gene Henson is a University of Connecticut certified Advanced Master Gardner.