Tomato hornworms can quickly devastate your tomato plants if left uncontrolled. These voracious eaters will feast on a plant’s leaves, leaving it looking twiggy and lifeless. Without the leaves, a tomato plant will be unable to grow and thrive and will threaten the hard work you’ve put into your tomato plants.
Tomato hornworms are large caterpillar-like creatures that camouflage easily on the stems and leaves of your tomato, pepper, and other garden plants. They are very easy to miss, even when you’re looking for them. They are the same shade of green as a tomato plant, and have white v-shaped marks along their sides. On the rear of the worm is a black “horn”. These worms are the larval stage of the hawk or sphinx or hummingbird moth. They hatch from small greenish-white eggs laid on the underside of leaves or stems by the hawk moth, and develop quickly into 3-4 inch hornworms over a period of about 4 weeks. The eggs laid by the hawk moth take on 4-5 days to hatch, and are easily hidden in a healthy tomato plant. If left alone, tomato hornworms will eventually burrow itself in the soil to pupate and create dark brown pupae, which will emerge as sphinx/hawk moths in the spring and start the process of destroying your garden over again.
Tomato hornworms will eat entire leaves, stems, and will even start munching immature fruit if they run out of stems and leaves. They will attack tomato plants, pepper plants, eggplants, potato plants, and even grape vines. I have seen their eggs laid on the stems and undersides of strawberry plants and bushes and shrubs as well. Because they camouflage so well into the plants they devour, you’re likely to notice their damage before you notice them. If you can catch them early in the process your plants will likely not be damaged too badly and will recover, but if left unchecked they can harm a plant to the point where it won’t have enough leaves to photosynthesize and produce fruit.
The best way to control tomato hornworms is to catch them early and hand-pick them off your plants. If your infestation of these pests is large, you may want to use BT (Bacillus thuringiensis) powder to kill them. BT powder works best before the hornworms have had a chance to reach full-size. If tomato hornworms are a problem year after year, try rototilling your soil in the fall or spring before your plant to destroy the pupae. Also, if you happen across any praying mantises in your yard, move them to your tomato plants – they will eat the hornworms if given the chance.
Some have said that companion-planting marigolds alongside your tomato plants will help deter tomato hornworms, but I have found that once your tomato plants take off and are several feet tall they are simply not in close enough proximity to the marigolds to really help. If you choose to hand-pick off tomato hornworms from your garden, the use of a black-light may come in handy. Hornworms will glow under a black-light at night and will be much easier to spot and dispose of.