Diamondback moth
The main cole-crop caterpillar — grazes leaves into pale windows and skeletonises the plant, and resists insecticides faster than almost any pest.
- Pest type
- Grazing caterpillar
- Attacks
- Leaves, heart, curd
- Worst in
- Cool, dry cole-crop season
- Main risk
- Extreme insecticide resistance
Overview
Diamondback moth (DBM) is the most important pest of cabbage, cauliflower, broccoli and other cole crops. The small greyish moth (with a diamond pattern on its folded wings) lays eggs on the leaves; the small, spindle-shaped green caterpillars graze the leaf tissue, usually from the underside.
Young larvae eat only one surface, leaving thin, pale, papery "windows"; older ones make holes and, in heavy numbers, skeletonise the leaves and bore into the heart or curd. DBM is famous worldwide for developing insecticide resistance extremely fast — it was the first crop pest to become resistant to Bt sprays — so the only durable approach is IPM: biologicals, traps, and strict rotation of a few remaining effective insecticides.
How to identify it
- Thin, pale, papery "windows" on the leaves where young larvae have grazed one surface, plus small irregular holes from older larvae.
- Small (up to ~1 cm), spindle-shaped green caterpillars that wriggle violently and drop on a silk thread when disturbed.
- Greyish moths with a pale diamond pattern along the back when the wings are folded, flying up at dusk.
- In heavy attacks, skeletonised leaves and larvae boring into the cabbage head or cauliflower curd.
The damage it does
- Leaf windows, holes and, in heavy attacks, skeletonised leaves that cut photosynthesis and stunt the plant.
- Larvae boring into the heart of cabbage or the curd of cauliflower, directly spoiling the marketable part.
- Contamination of the head/curd with larvae and frass, downgrading or rejecting the produce.
- Rapid resistance that makes repeated spraying of one product useless and worsens control over time.
When to act
- Scout leaf undersides twice a week from the seedling/nursery stage, since early control is easier and cheaper.
- Use pheromone traps to monitor moth flights and time action against young larvae.
- Act on the recommended threshold rather than by calendar, and never rely on repeated sprays of a single insecticide.
Organic & cultural control
- Spray Bacillus thuringiensis (Bt) against young larvae — the mainstay of DBM control, and rotate it with other modes of action.
- Grow a mustard trap crop around the cole crop (two rows per 25 rows of cabbage is a classic recommendation) to concentrate egg-laying, and manage the trap crop.
- Use pheromone traps for monitoring and mass-trapping, and conserve the parasitoid Diadegma/Cotesia and other natural enemies by avoiding broad-spectrum sprays.
- Overhead/sprinkler irrigation and neem sprays reduce larval survival; destroy crop residues after harvest.
Chemical control
- Because DBM resists insecticides so fast, strict rotation of modes of action is essential — CIB&RC-registered options include spinosad 45% SC, chlorantraniliprole, flubendiamide and emamectin benzoate, used in rotation, not repeatedly.
- Spray to cover the leaf undersides where larvae feed, and start with Bt on young larvae.
- Observe the pre-harvest interval strictly on cabbage and cauliflower, which are eaten directly.
- Confirm the current recommendation and rotation plan for your area with your local KVK.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My cabbage leaves have thin pale patches and small holes. What causes it?
That is diamondback moth. The young green caterpillars graze one surface of the leaf, leaving thin, pale, papery "windows", while older ones make holes and can skeletonise the plant. Look on the leaf undersides for small green caterpillars that wriggle and drop on a silk thread when touched.
Why do sprays stop working on diamondback moth so quickly?
DBM develops insecticide resistance faster than almost any pest — it was the first to become resistant to Bt sprays. Repeating one product quickly makes it useless. The answer is IPM: Bt on young larvae, a mustard trap crop, pheromone traps, conserving parasitoids, and strict rotation of the few remaining effective insecticides.
How does a mustard trap crop help?
Diamondback moth prefers mustard for egg-laying, so a couple of rows of mustard around the cabbage draw the egg-laying onto the trap crop instead of the main crop. You then manage the concentrated larvae there. It is a classic, low-cost IPM tactic that reduces the pressure and the number of sprays needed on the cabbage itself.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.