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Cabbage moth: how to recognise and treat it

Pest

Cabbage moth — Photo: picture taken by Olaf Leillinger, CC BY-SA 2.5, Wikimedia Commons

Symptoms

Smooth caterpillars without obvious hairs, yellowish green to brownish green or almost black, growing to 40–50 mm.
Young caterpillars feed in groups on the undersides of leaves and skeletonise them; they feed at night.
Older caterpillars bore into the hearts of cabbages, so damage shows when the head is cut.
Holes in the outer leaves and dark droppings on the plants.

Organic treatment

Pick off the white, round egg clusters and the caterpillars; check leaf undersides near the ground, and look at dusk when they feed.
Spray Bacillus thuringiensis (Bt), which works best on young caterpillars before they bore into the hearts.
Water on a nematode biological control sold for caterpillars, in cool, damp weather so the leaves stay wet.

Chemical treatment

Spinosad or pyrethrins on young caterpillars; follow the label dose and pre-harvest interval.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Prevention

Grow brassicas under fine netting or fleece that does not touch the leaves, so moths cannot lay eggs.
Check plants regularly from spring; the caterpillars are active mainly from July to September.
Dig or loosen the soil in autumn and keep weeds down — the pupae overwinter in the soil.
Spare parasitic wasps such as Trichogramma, which attack the eggs, and clear plant debris after harvest.

Plants it affects

Sources

Figures checked against these sources.