By David Marks

RECOGNISING CABBAGE BUTTERFLIES AND CATERPILLARS

Any butterflies or caterpillars on your crops are normally bad news! But just to get this particular pest identified you need to identify it at three stages of its life, the butterfly, the eggs and the caterpillars. The symptoms of Cabbage White Butterfly are as follows:

• Leaves will have holes in them
• The inner leaves of cabbages will often have been damaged
• Caterpillar “poo” will be left over the leaves and the hearts of cauliflowers
• Plants will be in poor health because of the leaf damage
• The physical presence of caterpillars will be obvious all over the leaves
• The underside of leaves will have  eggs on them

IDENTIFYING THE CABBAGE WHITE BUTTERFLY

The males and females are slightly different. Both have white wings with grey tips and are about 4.5cm / 1.8in wide. The males have one dark grey spot on each wing, the females have two spots on each wing.

The female butterflies lay eggs twice, sometimes three times in a season which hatch into caterpillars after a couple of weeks. Typically eggs are laid on the underside of leaves and to get an idea of size there would be about 25 on a 5p coin. Eggs tend to be laid 20 or so at a  time. The butterflies emerge in April / May time depending on your local weather. The eggs are shown in the picture below.

When the eggs begin to hatch the top of the eggs have black and white top to them which are the young caterpillars emerging.

Finally onto the caterpillars which do all the damage. There are two types, the pale green one and the green and black ones. Identifying them is a bit pointless in reality because any caterpillar on a brassica needs to be removed! However the picture below shows the more common black and green type of caterpillar.

LIFECYCLE OF THE CABBAGE WHITE BUTTERFLY

The diagram below shows the typical lifecycle of the Cabbage White Butterfly. There are two life cycle per season shown in the diagram but in favourable years this can increase to three. The damage is done at the caterpillar stage which is June to July and August to September.

The last egg laying of the season occurs in late August to September time depending on weather conditions. The eggs are laid on both the under and upper surface of leaves. The caterpillars emerge after a short time and begin to feed on the leaves of plants, typically members of the cabbage family.

When fully fed the caterpillars move away from their source of food and pupate (change into butterflies) on broken bark, fences and similar sites which are higher than the soil surface.

Cabbage white butterflies do not over winter in the ground although the Cabbage moth does. The large whites are unlikely to survive our winter but the small whites butterflies and moths definitely do survive.

PREVENTING AND TREATING CABBAGE WHITE BUTTERFLY

It’s important to remember with this pest that although the damage is done by the caterpillar the key to preventing damage is to stop the butterflies from laying eggs on your vegetables. If they do manage to lay eggs you can try to minimise the damage but in truth you will be fighting a loosing battle. Prevention is definitely the key to winning the battle against the Cabbage White Butterfly.

Chemical treatments are discussed below but the primary prevention measure is to cover your cabbages, cauliflowers and Brussels sprouts with some form of barrier to prevent the butterflies getting in. There are several options available which include Enviromesh, non-branded meshes, scaffold debris netting and horticultural fleece.

The principle behind all of them is to provide a covering which prevents insects getting in (including the Cabbage White Butterfly) but at the same time allowing air to circulate, water and light to enter freely. The costs, effectiveness and lifespan of each solution differ wildly so we have a devoted a special page which analyses in detail the pros and cons of various insect protection meshes and netting. The article also describes how to secure the netting to provide maximum protection. Click here for our page on insect mesh netting.

If Cabbage White caterpillars do manage to get onto your plants take action as soon as possible by removing as many as possible by hand. At the same time remove any eggs you see which are normally on the underside of the leaves.

The safest insecticide to use for Cabbage White Butterfly is one which is based on pyrethrum. Stronger chemical sprays include lambda-cyhalothrin. Always read the label of any insecticide for full instructions.

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