Article

How to End Hornworm Havoc

By Jolene Hansen

Meeting a hornworm face to face in your tomato patch is a moment you won't forget. These worms grow up to 4 inches in length, can get as fat as a finger, and have curved, posterior horns to boot. Two main types of hornworms trouble vegetable gardeners: the tomato hornworm and the tobacco hornworm. Tomato hornworms are more common in the North, while tobacco hornworms prevail in the South. But their territories and menus overlap. These voracious pests are often found working the same garden patch.

Hunting Down Hornworms

The first clue to a hornworm invasion usually comes with the discovery of leafless tomato plants. Not known as dainty eaters, these oversize pests cause extensive damage – fast! Fond of tomatoes and other plants in the same family, including tobacco, eggplants, peppers and potatoes, hornworms don't just create a few holes as they eat, they devour entire leaves overnight and feed on flowers and fruit, too. The upper parts of the plant are usually hit first.

Camouflaged by their fresh-green color, tomato and tobacco hornworms blend in against stems and leaves. Even when damage is widespread, these culprits avoid detection by easily hiding on plants during the day. Catch hornworms in action at dusk, dawn or nighttime, when these pests come out to feed in the open. Large, black droppings left on leaves and the ground below give clues to hornworm hideouts. They've also been known to reveal themselves if leaves are sprayed vigorously with a hose.

Understanding the Pest

Pest ID & Prevention

Tomato and tobacco hornworms are both immature, larval stages of large moths. The damage these worms cause in your garden is the same, but they have different markings. Tomato hornworms have a black horn on their rear with white, V-shaped marks pointing forward along their bright green sides. Tobacco hornworms have a red horn on their posterior and diagonal white stripes along their sides.

The adult moth forms of these hornworms are known regionally as sphinx moths, hawk moths or hummingbird moths. These large moths emerge in late spring and lay their eggs at night on plant leaves. Tomato and tobacco leaves are preferred, but related plants are used, too. Under optimal conditions, a single adult female moth can produce up to 2,000 eggs.1 Hornworms hatch in less than one week, and then dine relentlessly on your veggies for up to one month.2 With a life cycle of just 30 to 50 days, two or more generations per season are common.3

Eliminating Hornworm Problems

Handpicking hornworms and drowning them is an effective way to fight these pests – if you can find them while your plants are still standing or you don't mind spending time in dark gardens thinking about 2,000 4-inch worms. Colorado State University Extension reports that pesticides with the active ingredient carbaryl easily control hornworms.2

Carbaryl-powered GardenTech® Sevin® insecticide, which is available in dust, granular, concentrate, ready-to-use and ready-to-spray formulations, handles hornworms you see and those in hiding by working on contact and when worms ingest treated leaves. Known as a nonsystemic insecticide, Sevin® product doesn't penetrate vegetables or other plants; it simply hones in on pests, and then breaks down easily in the environment. Just follow label directions and guidelines for time between application and your veggie harvest.

Fighting Future Invasions

Hornworms overwinter in the soil in a pupae stage before becoming spring moths that start the season's hornworm troubles. Tilling your garden after your harvest and again in early spring can kill 90 percent or more of the overwintering pests and reduce hornworm problems for the coming year.3

Natural beneficial insects, part of a successful home garden integrated pest management program, help fight the hornworm battle, too. Beneficial parasitic wasps lay eggs that hatch and feed on hornworm hosts, spin cocoons and then emerge as new wasps ready to tackle more hornworms.3 So, a hornworm covered in a small silken cocoon is a strong sign that worm won't be doing more damage. Leave that cocoon-covered hornworm in your garden until the wasps emerge, and you'll have a homegrown army of beneficial insects.

As soon as you see signs of hornworm damage, you can put an end to their havoc. With the help of GardenTech® Sevin® insecticides and good garden practices, you can eliminate hornworms and enjoy a healthy, whole garden harvest.

Always read the product label and follow the instructions carefully.

GardenTech is a registered trademark of Gulfstream Home and Garden, Inc. Sevin is a registered trademark of Tessenderlo Kerley, Inc.

Sources:

1. Oklahoma State University Entomology and Plant Pathology, “Tomato Hornworm, Tobacco Hornworm," Oklahoma State University.

2. Cranshaw, W.S, “Hornworms and Hummingbird Moths," Colorado State University, August 2014.

3. Villanueva, J. Raul, “Tobacco Hornworm, Tomato Hornworm," University of Florida, November 2013.

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