large white butterfly

Symptoms

Large yellow + black hairy caterpillars 35mm long, voracious feeding leaving only midribs, egg clusters of 20-100 bright yellow eggs on leaf undersides.

Plants affected

• cabbage / broccoli / cauliflower / Brussels sprouts

Easily confused with

• cabbage moth

  How to tell them apart: Pieris brassicae (Large White) larvae are gregarious and feed in clusters on the OUTER leaves: they are yellow-green with conspicuous black blotches/spots, three yellow longitudinal stripes (one mid-dorsal, two lateral), and a covering of short white-grey hairs. Damage is open skeletonisation and ragged holes on exposed foliage, with dry granular green frass on top of the leaves. Mamestra brassicae (Cabbage Moth) larvae are smooth and HAIRLESS, green when young turning greyish-brown with a faint pale lateral line and a slightly humped rear segment; they bore DOWN INTO the heart of the head, tunnelling out of sight. Look for wet, sticky greenish-brown frass packed deep in the cabbage heart and internal galleries rather than surface feeding.

• diamondback moth

  How to tell them apart: The large white caterpillar is much larger when grown (up to ~40 mm), stout, yellow-green with conspicuous black blotches and a yellow dorsal and lateral stripe, covered in short fine hairs. Larvae feed gregariously in clusters, rapidly chewing large ragged holes and stripping leaves down to the veins, often on the upper leaves and growing heart. They leave heavy green-black droppings and do not drop on a silk thread when touched. The diamondback moth larva is small (max ~10-12 mm), slender, pale to bright green with a tapered body and a forked rear pair of prolegs. It feeds mostly on the underside of outer and lower leaves, scraping one surface to leave a thin transparent 'window' (window-paning) and small irregular holes. When disturbed it wriggles violently backwards and may drop on a silk thread. Pupae sit in a loose, open lacy silk cocoon on the leaf.

Common questions

How do I recognise large white butterfly on cabbage / broccoli / cauliflower / Brussels sprouts?

Large yellow + black hairy caterpillars 35mm long, voracious feeding leaving only midribs, egg clusters of 20-100 bright yellow eggs on leaf undersides.

Do I have to report large white butterfly?

No. large white butterfly is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is large white butterfly treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.