The juicy, lush flavor and rampant, easy-care growth makes tomatoes (Solanum lycopersicum) a garden favorite. While humans enjoy the sweet, tart flavor of the fruits, caterpillars are also attracted to the tomato plants, requiring quick action to remove the hungry invaders. Although the tomato plants will keep producing fruits, reducing the number of caterpillars on the plants will increase the harvest. Removal methods range from hand-picking to spraying insecticides.
About Tomato Plants
Although tomatoes are grown as annuals, the South American natives are tender perennials, hardy in U.S. Department of Agriculture plant hardiness zones 10 through 11. The mature fruits range from grape to softball size and may be green, yellow, orange, red or purple. The plants are sprawling and bushy with vine-like branches. They require full sun and at least 1 inch of water per week -- and more in hot weather.
Several different types of caterpillars infest tomato plants and their fruits. You can identify the pest by its appearance and the damage it causes.
The tomato hornworm (Manduca quinquemaculata) is a large, green and white striped, smooth-skinned caterpillar with a "horn" on its tail. It has a segmented appearance accentuated by the stripes. A hornworm can defoliate entire branches overnight. Tomato hornworms grow up to 3 1/2 inches long.
The alfalfa looper (Autographa californica) and cabbage looper (Trichoplusia ni) also feed on the foliage of a variety of plants, including tomatoes. Loopers are smooth green caterpillars that crawl by bringing their back legs forward, arching their backs, similar to an inchworm. They grow up to 1 1/2 inches long.
The tomato fruitworm (Helicoverpa zea) and tobacco budworm (Heliothis virescens) are similar in appearance, with young caterpillars ranging from cream to yellow and darkening to yellow-green or brown-red as they mature. Older caterpillars have tiny, thorn-like spines and grow up to 1 inch long. Both caterpillars attack and chew on the buds, blossoms and developing tomatoes. They enter the fruit by chewing a hole in the skin and then eat the inside of the tomato.
Variegated cutworms (Peridroma saucia) and black cutworms (Agrotis ipsilon) are among the cutworm species that attack new seedlings and tomato fruits. At night, the cutworm emerges from hiding in the dirt or plant debris and chews the tender stem of the seedling. It may also chew on the fruits, especially if the tomatoes are touching the ground. Cutworms are 1 to 2 inches long and smooth skinned. They curl up when touched.
Hand pick the caterpillars. Large caterpillars, such as the tomato hornworm, are easily hand picked from the tomato plant. Put on gloves if you're squeamish about touching caterpillars. Look at the plant and let your eyes follow the branch down the ragged stubs of the devoured leaves and eventually you'll see the fat green caterpillar amid the stems and leaves. Pluck it from the tomato plant and drop it into a bucket of soapy water.
Make cardboard collars to protect the tomato stems from cutworms. A simple 2 1/2-inch tall and 8-inch long cardboard collar formed into a circle and then pressed 1 inch into the soil surrounding the plant prevents the cutworm from encircling the stem and chewing it off. Alternately, cut off the bottom of a paper or plastic cup and insert the top portion of the cup into the soil to protect the tender stem.
Cultivate the soil after the harvest. By removing dead and dying vegetation and tilling the garden after the harvest, you can destroy many of the larvae and the pupae before winter. Fewer emerging moths in spring means fewer caterpillars to munch on your tomatoes next season.
Less Toxic Insecticides
In the home garden, targeting caterpillars with less toxic insecticides allows beneficial insects, such as bees, to continue to pollinate the other fruits and vegetables. In addition, using less toxic options means you can treat your tomatoes up to the day of harvest. Before mixing and applying any insecticides, put on gloves, safety goggles and a breathing mask to avoid contact with the insecticide. Always follow the manufacturer's instructions carefully.
Bacillus thuringiensis, a bacterium, is toxic to many caterpillar species, including hornworms, fruitworms, budworms and loopers. Mix a Bt concentrate at a rate of 1 to 3 teaspoons into 1 gallon of water for hornworms and 2 to 4 teaspoons into 1 gallon of water for other caterpillars. Spray the tomato's leaves until they are covered with the solution. Repeat weekly or as needed to control caterpillars.
Ready-to-use neem oil products may be used on a seven- to 14-day schedule. Apply the solution in the early morning or late evening to avoid burning the tomato plant. Shake the spray bottle well and spray the tomato plant until the leaves are soaked by the solution.
Spinosaid concentrate is mixed at 4 tablespoons per gallon of water and applied until the tomato plant is soaking wet. It kills infestations of loopers and other caterpillars. It may be reapplied four days apart and up to six times per year.