Hornworms can easily be identified because they are plump, green, and about four inches in length. They also have distinct V-shaped markings. According to Tammy's Recipes, hornworms are capable of causing extensive damage to tomato plants. Look toward the inside of the tomato plant during the day, and the outside of the tomato plant at night to find out if you have any tomato hornworms. If you spot any hornworms on your tomato plants, you will want to take action to get rid of them right away.
Look at your hornworm carefully. If you spot any white sacs that look like tiny pieces of cotton, no action is needed. This means that your tomato hornworms are infected with a parastic wasp. The wasp eggs will hatch and kill the hornworm for you.
Purchase a product with the active ingredient Bacillus thuringiensis (Bt for short). Bt is an all natural bacteria that will kill hornworms. This product comes in either a powder or a spray. The spray form is the easiest to apply.
Spray your tomato plants with the Bt product. Make sure you turn the leaves over and spray the underside. Sometimes hornworms will feast on the underside of the leaves. Do this on a day when rain and wind are not predicted.
Wait for the hornworms to eat the Bt and begin to die. This can take several days. You can then rinse the dead hornworms off of your tomato plants with a garden hose.