Insect pest infestation is one of the most frustrating aspects of tomato gardening. Your plants may look healthy and bear plenty of fruit one day, and before you can get to the ripened fruit a tomato pest insect has beat you to it, burrowing deep holes. General-purpose chemical insecticides may help, but they may also kill your best allies against these invaders: ladybugs, mantises and other insect predators. Tomato pest identification can help you tailor your control methods to target the pests and save the beneficial insects.
Stink bugs have gray or green shield-shaped carapaces and grow to about 3/4 inch long. They eat the tomato fruit and cause yellowish spots; the fruit becomes soft and spongy underneath the spots. They also leave their eggs in clumps on the leaves. If you find stink bugs or their eggs on your tomato plants, you can hand-pick them off and put them in a bucket of soapy water to kill them.
Snails and Slugs
Snails and slugs attack the fruit; snails eat the surface and slugs burrow into the fruit, leaving large ugly hollows. Slugs, which are snails without shells, are between a quarter inch to seven inches long, depending on species. You can deter these pests by using cages or stakes to support the plants and keep the fruit off the ground, and by placing slug beer traps around the plants.
This is a green caterpillar that gets its name from the horn on its rear end. The worm grows three to five inches long. It eats both the leaves and the fruit and may leave large holes behind. If you find just a few tomato hornworms on your plants, you can hand-pick them and kill them in a bucket of soapy water; for larger infestations you can apply Bacillus thuringiensis, a bacteria which attacks and kills the caterpillars but is harmless to people and pets.
The tomato pinworm is a tiny caterpillar; it grows to about a quarter inch in length. You may notice the small holes it leaves behind in the fruit and leaves of the tomato before you see the worm itself. The best control of this pest is to remove and dispose of any leaves or fruit you find with tunnels in them and clean up all plant debris at the end of the season to prevent the worms from finding shelter to survive the winter.
The cutworm gets its name from the damage it causes, cutting through the stems of young seedlings at ground level. The cutworm is a small gray grub, one to two inches long; if you observe cutworms around the base of your plants you can pick them off by hand. You can also protect your young tomato seedling from cutworms by placing a cardboard collar or toilet paper roll around the base of the stem at planting time.
Flea beetles, named for their tendency to jump when disturbed, are tiny (.06 to .12 inch long) black or brown beetles. They chew on tomato leaves, but this damage is secondary to the diseases that can enter through the wounds they leave in the plant. Insecticides containing carbaryl or permethrin are most effective at controlling flea beetles.
These are a few of the insects that may attack your tomato plants, but you may find others depending on your location. If you find insects that you can't identify, you can contact your local agricultural extension office for help with identification and control.