The most effective organic control for these green caterpillars on tomatoes is to simply hand pick them. They are a larger caterpillar and easy to spot on the vine. Hand picking them and placing them in a bucket of water is an effective way for how to kill tomato hornworms.You can also use natural predators to control tomato hornworms. Ladybugs and green lacewings are the most common natural predators that you can purchase.ommon wasps are also vigorous predators of tomato hornworms. These tomato caterpillars are also prey to braconid wasps. These tiny wasps lay their eggs on the tomato hornworms and the larva literally eat the caterpillar from the inside out.