Diamondback Moth
Plutella xylostella
Small grey-brown moth whose green caterpillars skeletonise brassica leaves. Globally resistant to many insecticides.
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Identify from a photoBackground
Diamondback moth is a near-worldwide pest of brassica crops. The tiny caterpillars feed on the underside of leaves, leaving distinctive 'window' damage where only the thin upper leaf layer remains. Populations can build fast in warm weather. Diamondback moth is one of the most insecticide-resistant pests in the world, which is why biological control and netting remain the most reliable home-garden approaches.
How to identify
- Adult: small (6mm long, 15mm wingspan) grey-brown moth with a row of pale diamond-shaped markings on the back when wings fold
- Larvae: pale green, 8-10mm when full grown, taper at both ends, wriggle backwards violently when disturbed
- Pupae: encased in fine silk cocoons on leaves or stems
- Damage: leaf windowing, small irregular holes, surface scarring; severe infestations defoliate young plants
Life cycle
Egg to adult in 2-3 weeks in warm weather. Multiple overlapping generations. In subtropical regions there can be 10+ generations per year.
Weather triggers
- Temperature: 12-32°C
- Warm dry conditions favour population build-up. Heavy rain physically knocks eggs and young larvae off plants.
Peak season (southern hemisphere)
Red = active season · Dark red outlined = this month
Affected vegetables & crops
Click any crop to see current prices and growing info.
Climate zones at risk
Organic & low-impact control
- Bacillus thuringiensis (Btk/Dipel). Effective but may be resisted in some regions, rotate with spinosad
- Fine insect netting over brassica beds
- Conserve parasitic wasps Diadegma semiclausum and Cotesia vestalis by avoiding broad-spectrum sprays
Chemical control
- Diamondback moth has developed resistance to most insecticide groups including many pyrethroids and spinosyns. Rotate modes of action aggressively if used
- For home gardens, Btk and targeted spinosad are the practical choices
Always read product labels. Registrations change.
Prevention
- Netting from seedling stage
- Avoid continuous brassica cropping in the same bed
- Remove crop residues promptly after harvest to break the life cycle
Companion planting
Flowering plants that support parasitic wasps (alyssum, coriander, dill, buckwheat) reduce caterpillar numbers. Strongly aromatic herbs at the edges offer modest deterrence.
Biosecurity
Widely established.
Know when Diamondback Moth is actually about
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