Cabbages and other brassicas can be extensively holed by caterpillar feeding by the end of summer.
What are cabbage caterpillars?
Caterpillars are the larval stage of various butterflies and moths. There are several species of caterpillar that feed on cabbages, other brassicas and other plants including turnip, swede, horseradish and nasturtiums. Large cabbage white butterfly caterpillars are yellow and black with obvious hairs on their bodies. Those of small cabbage white butterfly are pale green and covered in short, velvet-like hairs. Cabbage moth caterpillars are yellowish green or brownish green, with no obvious hairs on their bodies.
Holes are eaten in the outer leaves of all brassicas and damage may also be seen on the inner leaves of cabbages when the heart is cut through. Caterpillars and their excrement are often found on the plants.
There are three common caterpillar culprits:
- Large cabbage white butterfly (Pieris brassicae)
- Small cabbage white butterfly (Pieris rapae)
- Cabbage moth (Mamestra brassicae)
All three may be present at the same time. Caterpillars of cabbage moth and small white butterfly are more damaging as they bore into the hearts of cabbages, whereas the yellow and black caterpillars of the large cabbage white stay mostly on outer leaves.
- Inspect plants regularly and pick off the pale yellow butterfly eggs and caterpillars when seen
- Growing brassicas under fine netting or horticultural fleece can exclude adult butterflies and moths from laying eggs on the crop. Care must be taken to keep the netting off the crop or the adults can lay eggs through it.
- A biological control is available for caterpillars, this is a pathogenic nematode, Steinernema carpocapsae, available from Agralan Ltd., 01285860015, pestfreegardening.co.uk; Just Green Ltd, 01621785088, just-green.com; Organic Gardening Catalogue, 01932253666, organiccatalogue.com; Ladybird Plantcare, 08450945499, ladybirdplantcare.co.uk; Pippa Greenwood, pippagreenwood.com. The longer the treated caterpillars and foliage stay wet, the greater chance of the treatment being effective, so apply during cool dull weather.
- Spray with pyrethrum (e.g. Py Spray Garden Insect Killer, Bug Clear Gun for Fruit and Veg, Defenders Bug Killer, Growing Success Fruit & Veg Bug Killer, Growing Success Shrub & Flower Bug Killer), lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), or deltamethrin (e.g. Bayer Provado Ultimate Fruit & Vegetable Bug Killer). Pyrethrum has a one-day harvest interval and no restrictions on numbers of applications. For lambda-cyhalothrin and deltamethrin, read and follow the label instructions regarding each crop in general there is a seven-day harvest interval and a maximum of two applications can be made during the growing season (up to three applications for deltamethrin on cauliflower, broccoli, kale or Chinese cabbage)
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
Biological control suppliers (Adobe Acrobat pdf document listing biological controls available to gardeners).
- The adult butterflies and moths lay eggs on the underside of brassica leaves
- The butterflies have two generations during the summer; cabbage moth has one generation
- Large white caterpillars are likely to be seen in June-July and late August-September; small white caterpillars feed May-June and July-early September; cabbage moth caterpillars are active in July-September
- When fully fed, the caterpillars leave the plants to pupate
- Cabbage moth pupates and overwinters in the soil
- Cabbage white butterfly larvae pupate on suitable vertical surfaces above ground level
Common names Large cabbage white, small cabbage white and cabbage moth
Scientific names Pieris brassicae, Pieris rapae, Mamestra brassicae
Plants affected All brassicas, including cabbage, broccoli and Brussels sprout, some ornamental plants in the Cruciferae family, and nasturtiums
Main symptoms Holes in the leaves and presence of caterpillars
Most active May-October