IDENTIFYING HORNWORMS
Tomato and tobacco hornworms are closely related large, bright green caterpillars that feed on the leaves of tomatoes, as well as angel trumpet (Brugmansia and Datura species), tobacco, eggplant and occasionally peppers. 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.
CONTROL OPTIONS
One of the simplest methods for controlling hornworms, as well as many types of insects, is to pick them off plants and drop them into a bucket of soapy water. 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 from 0 to 21 days or more. If you already have ripening fruit on your tomato plants, be sure to choose a product with a short pre harvest interval.
ORGANIC PRODUCTS
Organic insecticides that control hornworms and other caterpillars include Bacillus thuringiensis, a bacterial disease that only effects caterpillars and is commonly referred to as B.t. B.t. is sold as Dipel, Thuricide, and several other brand names, and is most effective if applied when caterpillars are small. Spinosad is another option for controlling caterpillars organically. Derived from a soil dwelling bacterium, spinosad is the active ingredient in several insecticides, including Captain Jack’s Dead Bug Brew and Greenlight Spinosad Lawn and Garden Spray. Additional organic control options include products containing neem or pyrethrins. Because they break down quickly, most organic pesticides need to be reapplied more often than synthetic sprays to maintain plant protection. Check product labeling for application timing recommendations and restrictions.
SYNTHETIC PRODUCTS
Synthetic insecticides that control caterpillars include products containing one of the following active ingredients: carbaryl (commonly sold as Sevin), cyfluthrin, permethrin, and bifenthrin. 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.
BENEFICIAL INSECTS
