Tomato plants are susceptible to several types of pests, one of which is the tomato hornworm, or manduca quinquemaculata. These caterpillars are large and green with horn-shaped tails that contain v-shaped markings on their backs. Tomato hornworms can cause significant damage to a plant in as little as 24 hours. It is important to begin measures to control tomato hornworms the second they are spotted on your plants.
Pour 1 qt. hot water into a bucket and mix in 1 tsp. dish soap. Slide on a pair of gardening gloves and pick all of the tomato hornworms off of the tomato plants. Set the hornworms in the bucket of soapy water until they drown. This will work for smaller infestations.
Introduce a natural enemy to your tomato garden for larger infestations. According to the University of Minnesota, lady beetles, green lacewigs, paper wasps and braconid wasps all feed on the tomato hornworm and will keep the population under control.
Spray infected tomato plants with Bacillus thuringiensis, or Bt, as directed by the label instructions. Spray the tops of the leaves, and their undersides. This natural bacteria will be eaten by the tomato hornworm caterpillars, killing them from the inside out.