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Garden tomato

Most bugs on tomato plants are worth a look and not a spray. University of Minnesota Extension puts it plainly: there will always be some insect feeding on garden tomatoes, and you can still have a good crop from plants that show it. The pests that cost you tomatoes are the ones that cut down transplants in spring or bore into the fruit from midsummer on.

The list below runs in the order gardeners usually meet them. For five of the seven the useful natural enemy is already in the garden and there is nothing to buy. The job is to recognise it, and to avoid the broad-spectrum sprays that kill it. The releases worth paying for are Trichogramma against fruitworm eggs, and only where fruitworm is a known problem, and the predatory mite Phytoseiulus persimilis for spider mites, which is sold mainly for greenhouses and stops working above 86 °F (30 °C).

crop context · staked garden tomatoes, midsummer

Common tomato pests, in the order you meet them

AT TRANSPLANTING

Cutworms

Cut young plants off at the soil line overnight. Worst early in the season.

ReleaseGround beetlesNothing to release — give them cover
MAY–JUNE

Flea beetles

Small shot holes in the leaves. Seedlings suffer most; once plants have four or five leaves they usually survive the feeding.

ReleaseBraconid waspsNothing to release — the native parasitoid is not sold (UMN)
LATE SPRING

Aphids

Curled, sticky leaves. On tomato they rarely need treating, and hot summers knock many species back.

ReleaseHoverfliesWild — attract adults with open flowers
JULY ONWARD

Tomato hornworm

Strips leaves and scars fruit. Dark droppings give it away; hand-picking works.

ReleaseBraconid waspsNothing to release — leave the caterpillar where it is
AUGUST ONWARD

Tomato fruitworm

Bores into green fruit at the stem end. Damaging numbers rarely come before August.

ReleaseTrichogramma1–2 /ft² per release in gardens (Sound Horticulture)
LATE SUMMER

Brown marmorated stink bug

Pierces the fruit, leaving sunken white or yellow blotches with spongy tissue beneath.

ReleaseSamurai waspWild — conserve; not for release (not sold; interstate movement restricted)

Season calendar

TEMPERATE US · OUTDOOR TOMATOES · QUALITATIVE
JFMAMJJASOND
CutwormsJan: QuietFeb: QuietMar: QuietApr: BuildingMay: Pest pressure highJun: BuildingJul: QuietAug: QuietSep: QuietOct: QuietNov: QuietDec: Quiet
Flea beetlesJan: QuietFeb: QuietMar: QuietApr: BuildingMay: Pest pressure highJun: Pest pressure highJul: BuildingAug: BuildingSep: QuietOct: QuietNov: QuietDec: Quiet
AphidsJan: QuietFeb: QuietMar: QuietApr: BuildingMay: Pest pressure highJun: Pest pressure highJul: BuildingAug: QuietSep: BuildingOct: QuietNov: QuietDec: Quiet
HornwormsJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: BuildingJul: Pest pressure highAug: Pest pressure highSep: BuildingOct: QuietNov: QuietDec: Quiet
Spider miteJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: BuildingJul: Pest pressure highAug: Pest pressure highSep: BuildingOct: QuietNov: QuietDec: Quiet
FruitwormJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: QuietJul: BuildingAug: Pest pressure highSep: Pest pressure highOct: BuildingNov: QuietDec: Quiet
Stink bugsJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: BuildingJul: BuildingAug: Pest pressure highSep: Pest pressure highOct: BuildingNov: QuietDec: Quiet
Trichogramma (fruitworm)Jan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: QuietJul: Release windowAug: Release windowSep: Release windowOct: QuietNov: QuietDec: Quiet

Starter program

For a home garden, most of the program is things to leave alone. The one release in it is Trichogramma, and only where fruitworm has cost you fruit before. Bt is a spray, not a release, and belongs on small caterpillars only.

  1. AT TRANSPLANTINGGround beetlesNothing to release. Put a cardboard or foil collar round each stem, and leave mulch or a grassy edge where the beetles shelter.
  2. LATE SPRINGHoverfliesNothing to release. Keep flowers near the bed and leave aphid colonies that already have larvae working in them.
  3. MIDSUMMERBraconid waspsHand-pick hornworms, but leave any carrying white cocoons. The wasps that hatch from them will find the next ones.
  4. SMALL CATERPILLARSBt kurstakiLabel rate: Thuricide 1–3 tsp per gallon for tomato hornworm. Spray at the first droppings, while the caterpillars are small, and repeat weekly as needed. It kills butterfly caterpillars too, so spray only the tomatoes, and keep it out of drains and water.
  5. AT FIRST FRUITWORM EGGSTrichogramma1–2 /ft² per release in gardens, weekly through the egg-laying period. Check eggs a few days later: most parasitised ones turn black.

Setting up the garden

Most garden tomato pest problems are settled before anything is bought.

Collar every transplant

A collar of cardboard or foil, pushed a few inches into the soil and standing several inches above it, stops cutworms. Clear weeds at least two weeks before planting.

Skip broad-spectrum sprays

Carbaryl and many pyrethroids kill the predators that hold spider mites down. In hot weather, mite outbreaks can follow within days.

Water in dry spells

Water-stressed, dusty plants suffer most from spider mites. Watering, and hosing the leaf undersides hard and often, reduces their numbers, although it will not eliminate them.

Turn the bed over after harvest

Hornworms pupate in the soil. Tilling after harvest destroys pupae before they can emerge as next year's moths.