One summer morning, a tomato plant that looked fine yesterday has bare stems at the top.
Whole leaves are simply gone.
A green tomato lower down has a large, open scar across its skin.
You look closely and see nothing at first.
Then a fat green caterpillar, about as long as your finger, comes into focus.
It blends almost perfectly into the stem.
That is a hornworm, one of the best-known tomato pests.
This guide follows the tomato insect pests fact sheet from Clemson Cooperative Extension.
It covers hornworms and the other insects you are most likely to meet on tomatoes.
Start With Strong Plants
Clemson Extension notes that stressed plants tend to attract more insect pests than healthy ones.
So prevention starts with ordinary, steady care.
- Plant in a well-prepared, fertile bed.
- Spread mulch around the plants.
- Fertilize properly, ideally based on a soil test.
- Water steadily so the plants keep growing.
Check plants for pests before you buy them, too.
Clemson Extension suggests inspecting transplants carefully so you do not bring mites home.
A short walk through the garden every few days catches most problems early.
Look at the tops of the plants, the undersides of leaves and the green fruit.
Hornworms
What they look like
Two kinds of hornworm feed on tomatoes: the tobacco hornworm and the tomato hornworm.
Both are large green caterpillars that reach 3 to 3 and a half inches long.
Each has a horn-like spike near its tail, which gives the name.
The tobacco hornworm has seven diagonal white stripes on each side and a curved red horn.
The tomato hornworm has eight V-shaped marks on each side and a straight black horn.
The adults are large moths that are often seen hovering over plants at dusk.
The damage
Hornworms strip leaves from tomato vines.
In heavy outbreaks they also feed on the surface of the fruit, leaving large open scars.
Clemson Extension notes that leaf loss is much more common than fruit damage.
Damage usually begins in midsummer and continues through the rest of the season.
Hornworms also feed on pepper, eggplant and related plants.
Their life cycle
Hornworms spend the winter in the soil as pupae.
The moths come out in early summer and lay eggs on the undersides of leaves at night.
Each moth leaves only one to five eggs on a plant per visit.
Caterpillars hatch in about four days and feed for about three weeks.
Then they burrow into the soil to change into moths.
In warm regions there are usually at least two generations a year.
Hand-Pick Hornworms Calmly
In a home garden, Clemson Extension calls hand-picking an effective way to control hornworms.
Start where leaves are missing at the top of the plant.
Follow the bare stems down slowly until you spot the caterpillar.
Their green color hides them well, so look from a few different angles.
Drop each one into a bucket of soapy water.
A few minutes of checking every couple of days keeps them under control.
Leave Hornworms With White Cocoons
Sometimes a hornworm carries small white projections on its back.
These are the cocoons of tiny beneficial wasps.
Clemson Extension explains that the wasps lay eggs inside the hornworm, and the young feed inside it.
Then they spin cocoons on its back.
A hornworm in this state has stopped feeding.
If you find one like this, leave it in place.
A new generation of wasps will hatch and go after more hornworms.
Tomato Fruitworms
Clemson Extension calls the tomato fruitworm the most damaging tomato insect pest in South Carolina.
The same insect is known as the corn earworm on sweet corn.
The adult is a yellowish-olive moth that lays single eggs near flowers and fruit.
The young caterpillars bore into fruit soon after they hatch, often at the stem end.
They prefer green fruit.
The holes cause direct damage and invite rot.
Usually only one caterpillar is found in each fruit.
Check green tomatoes for small holes near the stem, and remove damaged fruit.
Fruitworms spend the winter as pupae in the top 2 inches of soil.
Stink Bugs and Leaf-Footed Bugs
These bugs feed on ripening tomatoes and many other vegetables.
They pierce the fruit with needle-like mouthparts and suck the sap.
Fruits punctured while young can grow up deformed.
Adult stink bugs are shield-shaped.
Green stink bugs are bright green, and brown stink bugs are dull grayish-yellow.
Leaf-footed bugs are dark brown with a cream stripe and flattened, leaf-like hind legs.
Their young look similar but smaller, and leaf-footed bug nymphs are bright orange-red.
Stink bugs spend the winter as adults along ditch banks, fence rows and roadsides.
They build up on wild plants and move into gardens as those plants mature.
Numbers often peak from July into early October, so watch ripening fruit closely then.
Aphids, Whiteflies and Spider Mites
Several smaller pests feed on tomato sap.
Potato aphids
Potato aphids are soft, pear-shaped insects about an eighth of an inch long.
They may be pink, light green, or mottled green and pink.
Heavy feeding can curl new growth, make blossoms drop and spread plant viruses.
Our guide to aphids in the vegetable garden covers gentle control steps.
Silverleaf whiteflies
These tiny, whitish-yellow insects gather on the undersides of leaves.
They suck sap and leave sticky honeydew, where black sooty mold can grow.
They can also spread viral diseases of tomatoes.
Two-spotted spider mites
Spider mites are about the size of the period at the end of a sentence.
Their feeding leaves fine pale flecks, and the leaves can turn grayish.
A hand lens helps you see them.
Protect the Helpful Insects
Clemson Extension notes that beneficial insects help control aphids, leafminers and hornworms.
The small wasps that attack hornworms are a good example.
Broad sprays kill these helpers along with the pests.
That is why Clemson Extension advises using insecticides only when necessary.
When a Spray Is Needed
Many home gardens need little more than hand-picking and steady care.
If pests get out of hand, start with the gentlest option.
Clemson Extension lists insecticidal soap for aphids, whiteflies and spider mites.
Our guide to insecticidal soap explains how to use it safely.
Spinosad is a natural product that controls caterpillars.
Clemson Extension notes that it is easier on beneficial insects than broad-spectrum products.
Whatever you use, check the label for the waiting time between spraying and harvest.
Follow every direction and precaution on the label.
A Simple Tomato Pest Checklist
- Keep plants healthy with good soil, mulch and steady water.
- Inspect transplants before you bring them home.
- Walk the garden every few days and look under leaves.
- Hand-pick hornworms when you see bare stems.
- Leave hornworms that carry white cocoons.
- Check green fruit for small holes near the stem.
- Watch for stink bugs from midsummer into fall.
- Use soap or spinosad only when needed, and follow the label.
A Calm Way to See It
Finding a hornworm can feel alarming the first time.
In truth, a few minutes of looking each week keeps most tomato pests in check.
For leaf spots, cracks and other troubles that are not insects, see our guide to common tomato problems.
Sources and Further Reading
- Clemson Cooperative Extension, Home and Garden Information Center — Tomato Insect Pests: supports the identification, damage and life cycles of hornworms, fruitworms, stink bugs, leaf-footed bugs, potato aphids, whiteflies and spider mites, hand-picking, parasitized hornworms, beneficial insects and the use of soap and spinosad.
- Clemson Cooperative Extension — Insecticidal Soaps for Garden Pest Control: how to use soap sprays on soft-bodied pests.
- Clemson Cooperative Extension — Tomato Diseases and Disorders: tomato problems that are caused by disease or weather rather than insects.