How to Fight Hornworms

Arm yourself with knowledge, a keen eye, and a few pest-control tools to hunt down and eliminate this arch nemesis of your tomato plants.

Photo by Getty Images/Lawrence Glass

One July day, in two 80-foot rows of tomatoes in our hoophouse at Twin Oaks Community, I found 42 hornworms varying in length from 1 to 4 inches — a collective total of 85 inches of pests! They were stripping the tomato leaves and munching on the green fruit.

Hornworms are large caterpillars capable of doing serious damage to tomato crops. The most common hornworm species in the garden is the tomato hornworm (Manduca quinquemaculata), but both the tomato hornworm and its cousin the tobacco hornworm (M. sexta) are bad news, and both attack tomato plants. Before Twin Oaks was established here in Virginia (Zone 7a) in 1967, the land had been a tobacco farm, so we have a lot more tobacco than tomato hornworms on our property.

Hornworms in their caterpillar forms feed on plants exclusively in the nightshade family, and have a strong affinity for tomato plants. Their adult forms are moths — the five-spotted hawk moth for the tomato hornworm, and the sphinx moth for the tobacco hornworm. This year, I caught one of the moths and killed it before it could lay too many eggs, but we still have plenty of caterpillars. Even our most vigilant caterpillar hunting seems to miss some.

Though it may feel impossible to get rid of these tomato terrors once they hatch, you can catch them before they take a strong hold by recognizing the signs of hornworm damage, knowing where to look for the caterpillars, and utilizing some tools and insect allies to rid your garden of a most unwelcome pest.

 Searching for Signs

The first step to claiming victory over hornworms is to know the signs of their damage. We conduct hunting raids every morning. If you can’t check daily, look for them at least twice a week in the summertime. A good first place to check is the tomato plants’ upper leaves. If they’re stripped bare down to the ribs, hornworms are probably nearby; the caterpillars only like the tender upper leaves. If the older leaves are damaged but the newer, younger leaves are intact, it may mean there was a hornworm, but it’s been removed already, and the plant is recovering.



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