Tomato hornworms are a large caterpillar that eats many parts of the tomato plant. The large size of these pests allows them to rapidly defoliate tomatoes, potatoes, eggplants, and peppers. Handpicking is one method of control. You can also use Dipel DF (OG), (Bacillus thuringiensis subsp. Kurstaki) to control tomato hornworms.