Cabbage white caterpillars
Green or yellow-green caterpillars of white butterflies that chew large holes in cabbage-family leaves and foul the hearts with droppings.
Also known as: Cabbage worms, Cabbage white butterfly
Symptoms and identification
Large, ragged holes in leaves, with the midrib often left, and green droppings in the centre of cabbages, cauliflowers and broccoli. Small yellow bottle-shaped eggs or clusters appear on the underside of leaves, and white butterflies flutter over the plants.
Causes
Female butterflies lay eggs on brassica leaves from spring to autumn. In warm climates, several generations occur in a season, and the caterpillars grow quickly.
Organic treatment
Hand-pick caterpillars and eggs. Spray Bacillus thuringiensis (Bt), which affects only caterpillars, on young larvae and repeat after rain.
Prevention
Cover plants with fine insect mesh from planting, supported so it does not rest on the leaves. Check leaf undersides weekly and squash eggs. Plant nasturtiums away from the crop only if you want to attract the butterflies elsewhere.
Chemical treatment (use with care)
Use an insecticide labelled for caterpillars on brassicas, such as one containing spinosad, following the label and harvest wait.