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Cabbage, broccoli & kale

Cabbage, broccoli, kale, cauliflower, collards and Brussels sprouts all draw the same pests, so one list covers them. Transplants are most at risk. Cabbage maggots eat the roots of early spring plantings, and flea beetles pepper the leaves of seedlings. Then come the caterpillars: the imported cabbageworm, the diamondback moth and the cabbage looper. Kentucky's extension entomologists advise identifying the caterpillar first, because different species may respond to different insecticides.

Bt works on all three while they are small, and it spares the parasitic wasps that attack them. Row cover from planting keeps most of these pests off in the first place. In autumn, cabbage aphids build in cool weather, and they can make kale inedible.

crop context · kale and cabbage bed, early summer

Common cabbage, broccoli and kale pests, in the order you meet them

EARLY SPRING PLANTINGS

Cabbage maggot

Eats the roots. Transplants wilt, turn blue-grey and stunt, and some die.

ReleaseSteinernema feltiae100,000–125,000 infective juveniles per transplant (UMass)
APRIL–MAY

Flea beetles

Shot holes in seedling leaves. Plants past the five-leaf stage tolerate a few beetles.

ReleaseBraconid waspsNothing to release — the native parasitoid is not sold (UMN)
FROM THE FIRST WHITE BUTTERFLIES

Imported cabbageworm

Velvety green caterpillars along the midrib, feeding towards the centre of the plant.

ReleaseBt kurstakiLabel rate — Thuricide 1–3 tsp per gallon
SPRING & AUTUMN

Diamondback moth

Small caterpillars that wriggle when touched. They do most harm to young plants and growing points.

ReleaseBt kurstakiLabel rate — Thuricide 1–2 tsp per gallon for diamondback moth
LATE SUMMER

Cabbage looper

Arrives late in the North. Large loopers are harder to control than small ones.

ReleaseTachinid fliesWild — keep nectar plants near the crop, no broad-spectrum sprays
AUTUMN

Cabbage aphid

Grey, waxy colonies that curl the leaves and pack into heads. Worst in cool autumn weather.

ReleaseHoverfliesWild — plant alyssum, dill, cilantro or Ammi majus near the brassicas
SPRING–AUTUMN · SOUTH

Harlequin bug

Red-and-black shield bug that leaves white blotches. Not known to overwinter north of about 40° N.

ReleaseNo release availableNothing to buy — fine netting and hand-picking; egg parasitoids are wild
MID-MAY–OCTOBER · NORTHEAST

Swede midge

Tiny larvae in the growing point leave broccoli and cauliflower blind or multi-headed, with brown corky scars.

ReleaseNo release availableNothing to buy — rotate 2–3 years and grow under fine netting on clean ground (UMass)

Season calendar

TEMPERATE US · SPRING AND AUTUMN CROPS · QUALITATIVE
JFMAMJJASOND
Cabbage maggotJan: QuietFeb: QuietMar: QuietApr: BuildingMay: Pest pressure highJun: BuildingJul: QuietAug: BuildingSep: BuildingOct: QuietNov: QuietDec: Quiet
Flea beetlesJan: QuietFeb: QuietMar: QuietApr: BuildingMay: Pest pressure highJun: BuildingJul: BuildingAug: BuildingSep: QuietOct: QuietNov: QuietDec: Quiet
Imported cabbagewormJan: QuietFeb: QuietMar: QuietApr: QuietMay: BuildingJun: BuildingJul: Pest pressure highAug: Pest pressure highSep: BuildingOct: BuildingNov: QuietDec: Quiet
Diamondback mothJan: QuietFeb: QuietMar: QuietApr: BuildingMay: Pest pressure highJun: Pest pressure highJul: BuildingAug: BuildingSep: Pest pressure highOct: BuildingNov: QuietDec: Quiet
Cabbage looperJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: QuietJul: BuildingAug: Pest pressure highSep: Pest pressure highOct: BuildingNov: QuietDec: Quiet
Cabbage aphidJan: QuietFeb: QuietMar: QuietApr: QuietMay: QuietJun: BuildingJul: BuildingAug: BuildingSep: Pest pressure highOct: Pest pressure highNov: BuildingDec: Quiet
Harlequin bug (South)Jan: QuietFeb: QuietMar: BuildingApr: Pest pressure highMay: Pest pressure highJun: BuildingJul: BuildingAug: BuildingSep: Pest pressure highOct: BuildingNov: QuietDec: Quiet
Nematodes (cabbage maggot)Jan: QuietFeb: QuietMar: QuietApr: Release windowMay: Release windowJun: QuietJul: QuietAug: QuietSep: QuietOct: QuietNov: QuietDec: Quiet

Starter program

For a home garden the program is row cover, a nematode treatment at planting, and Bt on small caterpillars. Everything else is conserving what is already there.

  1. AT TRANSPLANTINGSteinernema feltiae100,000–125,000 per transplant, sprayed or soaked onto the tray before planting or drenched in at planting. Repeat if the fly arrives more than a week later, and keep the soil moist.
  2. AT TRANSPLANTINGRove beetlesNothing to release. Aleochara bilineata emerges just after the maggot flies begin laying, and eats their eggs and larvae.
  3. FIRST WHITE BUTTERFLIESBt kurstakiLabel rate: Thuricide 1–3 tsp per gallon for cabbageworm, 1–2 tsp for diamondback moth. Spray while caterpillars are small, before they enter the heads. Repeat weekly as needed and after heavy rain.
  4. SUMMERBraconid waspsNothing to release. Leave parasitised caterpillars and clusters of small cocoons on the plant, and grow sweet alyssum or buckwheat nearby.
  5. LATE SUMMERHoverfliesNothing to release. Alyssum, dill, cilantro or Ammi majus near the bed draw them to cabbage aphid colonies. Alyssum is itself a brassica and attracts flea beetles.

Setting up the garden

The brassica bed is protected at planting, not rescued at heading.

Cover from the day you plant

Row cover or fine netting, sealed at the edges, keeps out cabbage maggot flies, flea beetles and egg-laying moths and butterflies. Don't plant where brassicas grew last year.

Check transplants before they go in

Diamondback moth, including insecticide-resistant strains, travels north on transplants raised in the South.

Scout from the first white butterflies

Look under the lower leaves and pull back the wrapper leaves to check the growing point. Small caterpillars are the ones that are easy to kill.

Clear the bed after harvest

Cabbageworm pupae, cabbage aphid eggs and harlequin bugs all overwinter on old stems and debris. Take them out or dig them in.