Cabbage caterpillars

What are cabbage caterpillars?

Caterpillars are the larval stage of various butterflies and moths. There are several species that feed on cabbages and allied brassica plants. Large cabbage white caterpillars are yellow and black with obvious hairs on their bodies. Those of small cabbage white 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.

Symptoms

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 the outer leaves.

Control

Non-chemical control

• Inspect plants regularly and pick off the pale yellow butterfly eggs and caterpillars when seen
• A pathogenic nematode, Steinernema carpocapsae, is available by mail order from some suppliers of biological controls as well as some garden centres. The microscopic worm-like nematodes are sprayed or watered on to the foliage, preferably in the evening when the leaves are likely to stay wet for longer. The nematodes enter the caterpillars’ bodies and infect them with a bacterial disease

Chemical control

• Spray with pyrethrum (Py Spray Garden Insect Killer, Scotts Bug Clear Gun for Fruit & Veg, Doff All In One Bug Spray, STV Time's Up Bug Killer), lambda-cyhalothrin (Westland Plant Rescue Fruit & Vegetable Bug Killer), or deltamethrin  (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, there is a seven-day harvest interval and two applications can be made during the growing season (up to three applications for deltamethrin on cauliflower, broccoli, kale or chinese cabbage)

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

• 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