Agricultural and Natural Resources Technician
Franklin County Cooperative Extension Service
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What is a Horn Worm Called if it is found on a tomato plant?
“Give up”? It’s a Tomato Horn Worm!
Tomato hornworms are large, bright green caterpillars that feed on the leaves of tomatoes, as well as tobacco plants. They have a distinct single spine or “horn” on their rear end, but cannot sting. These caterpillars will reach up to four inches in length before maturing into large grey moths.
Despite their large size, hornworms are not usually noticed until they strip a considerable amount of foliage from a tomato plant, which can happen in a matter of a few days if several caterpillars are feeding on the same plant. If left unchecked, hornworms can devour all of a tomato plant’s foliage, severely weakening the plant. Hornworms will continue to multiply through the rest of the growing season, making control now and throughout the summer essential to keep your tomatoes productive.
One of the simplest methods for controlling hornworms is to pick them off the plants and dispose of them. Controlling hornworms by hand picking requires almost daily inspection to stay on top of the population. Adult hornworms, known as sphinx moths, lay new eggs every night, and each female can lay up to 2000 eggs during her short life span.
A less labor-intensive way of controlling hornworms is to spray tomato plants with an appropriate insect control product. Several insecticides are effective, with products containing organic and synthetic active ingredients available at local garden centers. When applying any insecticide be sure to read and follow all label directions and pay careful attention to the pre harvest interval. This is the number of days you must wait between the time you spray the plant and the time you harvest. Pre harvest intervals vary among insecticides.
If you already have ripening fruit on your tomato plants, be sure to choose a product with a short pre harvest interval. Check product labeling for application timing recommendations and restrictions. Active ingredients of all pesticides are listed on the product container and can usually be found on the front of the packaging. When treating tomatoes and other garden plants, be sure to only use products that are labeled for spraying vegetables. Spray late in the evening to minimize impacts on bees and other pollinators.
This hornworm is covered in parasitic wasp cocoons. Gardeners occasionally find hornworms in their garden that have white cylindrical attachments all over their backs. These are the cocoons of a type of parasitic wasp, which feed on in this case hornworms, as they develop, eventually causing them to die. Parasitic wasps are very small and do not sting people. If you find a caterpillar in your garden that has been attacked by parasitic wasps, leave it there so the wasps may continue to develop. When mature they will hatch out of the cocoons and feed upon the Hornworm they are attached too.
Hornworm with parasitic wasp cocoons attached
For more gardening information and ways to control insects in the garden contact Franklin County Cooperative Extension at 919-496-3344 or visit our website at www.ces.ncsu.edu.