Cabbage Worms & Loopers
TreatablePest · does not spread · also called cabbage white caterpillar, imported cabbageworm
If you have white butterflies over your brassicas, you will shortly have caterpillars in them. The damage is ragged holes rather than clean edges, and the frass accumulating in the centre of a cabbage or lettuce is often the first thing noticed.
What it looks like
Velvety green caterpillars, well camouflaged along the midrib, chewing ragged holes through leaves. Green-brown pellets of frass collect in the heart of the plant. White butterflies fluttering around the bed are the adults.
How to confirm it
- Ragged irregular holes through the leaf, not neat edges or notches.
- Green frass pellets in the crown of the plant.
- Caterpillars lie along the midrib where they are nearly invisible.
- White or cream butterflies over the bed in the weeks before.
What to do
- 1Hand-pick, checking along midribs and in the heart of the plant.
- 2Bt or spinosad are effective and specific to caterpillars.
- 3Floating row cover from planting is the most reliable answer — it stops the butterflies laying at all.
What it gets confused with
One observation settles each of these.
Slugs leave slime trails and irregular holes with smooth edges, and feed at night. Caterpillars leave frass.
Flea beetles make many tiny round shot-holes rather than a few large ragged ones.
Preventing it next time
- Cover brassicas with fine mesh from the day they go in.
- Grow flowering plants nearby to support parasitic wasps.
Plants affected
Check these two things first
- Push a finger into the soil, two knuckles deep. Wet soil plus a wilting plant means too much water, not too little — and it is the commonest reason a plant is dying. Dry soil plus crisp leaves means the opposite. The leaves look nearly identical either way, so the soil is what tells you.
- Turn a damaged leaf over. Half of all diagnoses live on the underside: fuzz means downy mildew, fine webbing means spider mites, clusters of insects mean aphids. Nothing on the top of a leaf is as informative.
Most garden problems are cosmetic and resolve without treatment. Reach for a spray last, not first.