Cabbage white caterpillars
Caterpillars of the large and small cabbage white (Pieris brassicae, P. rapae) eat brassica leaves, often to the point of stripping them. The large white feeds in groups on the outer leaves; the small white feeds singly and bores into the head.
Symptom photos
Symptoms
- Irregular holes and chewed-out sections of the leaf blade
- Yellow-and-black caterpillars feeding in groups on leaf undersides
- Green, solitary caterpillars hidden along the midrib
- Dark green pellets of frass in the heart of the plant
- Yellow egg clusters on the underside of leaves
What it does to the crop
- Leaves skeletonised and the crop lost entirely in a mass attack
- Heads fouled with frass that is hard to remove
- Damage opening the way to bacterial rots
- Plants weakened and growth checked
What encourages it
- A warm, sunny summer that suits butterfly flight
- Two to three generations a season, from May to September
- Brassicas grown without protection
- No natural enemies, such as parasitic wasps
Prevention
- Cover with insect mesh or fleece for the whole season
- Inspect leaf undersides and wipe off egg clusters
- Pick caterpillars off by hand on a small plot
- Attract parasitoids with umbellifer flowers
- Clear crop debris after harvest
⚠️ Before you reach for a spray
This atlas is informational and still growing — different diseases can look almost identical. Confirm the diagnosis and read the product label before applying any plant protection product. If you are unsure, ask your local extension or advisory service.
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