How To Deal With Cabbage white butterfly in Your Irish Garden
What is Cabbage white butterfly?
The large cabbage white butterfly is one of Ireland's most familiar garden butterflies, but its caterpillars are also one of the most destructive pests of brassica crops. Two species cause damage — the large white (Pieris brassicae) with its black-tipped white wings, and the small white (Pieris rapae) which is slightly smaller and less conspicuous. Both species lay eggs on brassica plants, with the large white laying conspicuous clusters of yellow eggs on leaf surfaces and the small white laying single eggs. The bright yellow-and-black caterpillars of the large white are gregarious and feed in groups, while the green caterpillars of the small white are solitary and harder to spot.
Damage Caused by Cabbage white butterfly
Large white caterpillars feed gregariously, starting on outer leaves and working inward, capable of reducing cabbage, broccoli and cauliflower plants to stripped skeletons of stems and midribs within days. Small white caterpillars bore into the hearts of cabbages and the florets of broccoli and cauliflower, contaminating crops with frass. Both species also attack Brussels sprouts, kale, nasturtiums, and other brassicas. Two to three generations may occur per year in Ireland, with damage most severe from June through October.
How to Prevent Cabbage white butterfly
Cover all brassica crops with fine insect mesh netting immediately after planting, ensuring no gaps where butterflies can enter. Inspect plants regularly from May onwards, checking the undersides of leaves for eggs — large white eggs are in conspicuous yellow clusters while small white eggs are single and pale. Pick off eggs before they hatch. Companion plant with strongly scented herbs and grow nasturtiums nearby as a trap crop. Encourage natural parasitoid wasps which attack cabbage white pupae.
How to Treat Cabbage white butterfly
Hand-pick caterpillars daily during the peak season — wear gloves as large white caterpillars release a foul-smelling yellow liquid when handled. Spray with Bacillus thuringiensis (Bt) for effective biological control — Bt is a naturally occurring bacterium that kills caterpillars but is harmless to beneficial insects, birds and mammals. Apply when caterpillars are small for best results. Organic pyrethrum provides knockdown control for heavy infestations. Encourage garden birds, particularly blue tits, which consume large numbers of caterpillars.
Cabbage white butterfly in Ireland
Cabbage white butterflies are abundant throughout Ireland with populations building from May onwards. The mild Irish climate allows two to three generations per year in most areas, with continuous caterpillar damage from June through October. The large white population is supplemented by annual migrations from continental Europe, adding to the locally bred population. Irish organic brassica growers consider mesh netting essential — it is by far the most reliable protection method. The increasing popularity of kale in Irish diets has led to more awareness of cabbage white damage.
Plants Affected by Cabbage white butterfly
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