Tomato hornworms and Tobacco hornworms are often confused for one another but nonetheless are both very destructive pests that are common in North America. They both attack tomato, potato, eggplant, pepper and tobacco plants. Hornworms feed on the leaves, small stems and fruit of the aforementioned plants. They have voracious appetites and despite their large size are difficult to spot as they blend in well with the foliage. They both damage plants in a similar manner and likewise can be controlled and prevented using the same techniques.
Identify Tomato and Tobacco Hornworms
Tomato hornworms are green caterpillars with white v-shaped marks along its body that grow up to 5 inches long and have a black horn projecting from its rear. Tobacco hornworms are also green with white stripes diagonally across its body and have a red horn on its rear. Their horns are fake and incapable of stinging, so no worries there!
Tomato hornworms are the larvae of the Five-Spotted Hawk Moth while tobacco hornworms are the larvae of the Sphinx Moth. Both these moths lay their eggs on the underside of leaves of their favorite plants. Eggs hatch in 4-7 days.
Hornworm eggs are round and greenish-white and will mostly be found on the underneath of leaves of the plants they relish!
Signs of an infestation
Dark green/black dropping on leaves or stems of the plant you’re inspecting or on the ground around the plant is a sure shot sign of a hornworm infestation! Stems with missing leaf bits, wilting leaves, small bites in immature fruit are also signs of an infestation.
Controlling and Preventing Tomato and Tobacco Hornworms Organically
Till the soil: Rototilling soil in and around planting area after harvest and before planting the next batch will without doubt get rid of overwintering pupae of the hornworm. Performing this activity can cause greater than 90% mortality of pupae as pupae are quite large and are not buried deep in the soil.
Handpick the bugs: Hornworms do not like sunlight so they generally are slugging it around in the shade. Put on your gloves and go about scouting your plants for the hornworms. Splashing soapy water on the plant can help knock those unsuspecting caterpillars off their perch or in the least will make them writhe about revealing their position! Look underneath leaves as they generally preside there. Just drop them off into a bucket of soapy water to kill them or squish them if that makes you happy!
Seek and kill hornworm eggs: Late spring is when, hornworm moths tend to mate and lay eggs underneath leaves of aforementioned plants. It would be best though, if you look out for these pests and their eggs all season long!
Use organic pesticides: Bacillus thuringiensis (BT) is a natural insecticide that is especially effective on small larvae and works by attacking the stomach of particular insects. It is sold commercially as Dipel and Thuricide and is considered to be safe environmentally and for humans. Some growers use it even before an infestation as a precaution. However, do your research and get advice from a local specialist beforehand.
Beneficial insects: Wasps, in particular barconid wasps are known to prey on hornworms by parasitizing them with eggs of their own. Hence, while removing hornworms if you spot one with white wasp cocoons/white egg sacs in them let them be. The eggs will hatch in time giving rise to more wasps that feed on those dreaded hornworms! Other beneficial insects are lacewings, ladybugs and trichogramma wasps.
Plant trap/ally crops: Hornworms absolutely love dill and more often than not go for them instead of your tomato plants! Once they have infested your dill, you can easily get rid of them. Marigolds and opal basil are known to be beneficial when planted nearby.
Homemade moth deterrent: A mixture of garlic, insecticidal soap and red pepper powder diluted with water sprayed on your plants will keep the sphinx and hawk moth out of your garden as they dislike the smell of this solution, thus preventing them from laying their eggs.