Cabbage white: controlling caterpillars on cabbage naturally
The cabbage white is one of the best-known butterflies in the vegetable garden – and one of the most feared. It is not the white butterfly itself that does the damage, but its voracious caterpillars: within a few days they can strip cabbage, kohlrabi, broccoli, Brussels sprouts and radishes down to the leaf ribs.
There are two species, the large and the small cabbage white. Both prefer to lay their eggs on brassicas. Anyone who looks early and takes preventive action can prevent the feeding damage almost entirely with simple, natural means.
In short
- The white butterflies lay yellow eggs on the undersides of brassica leaves.
- The green or yellow-and-black caterpillars eat large holes and leave droppings behind.
- Best remedy: an insect-proof net right from the start.
- Also: collect eggs and caterpillars, mixed culture, encourage beneficial insects.
How to spot an infestation
The first warning signs are the white butterflies fluttering over the beds in spring and summer. Shortly afterwards you will find small, elongated yellow eggs on the undersides of the leaves – in groups for the large cabbage white, singly for the small one. The caterpillars that hatch are velvety green (small) or yellow-green with black dots (large). Typical are large feeding holes, nibbled leaf edges and crumbly, green-black droppings in the hearts of the leaves.
The damage the caterpillars cause
The caterpillars first eat holes, later whole leaves down to the ribs. Particularly annoying: they bore into the hearts of headed cabbage, broccoli and Brussels sprouts, soil them with droppings and make the harvest inedible. Young plants can collapse completely under heavy infestation.
Preventing the cabbage white
- Insect-proof net: by far the most effective measure. Lay a fine-meshed net (mesh size approx. 0.8–1.4 mm) over the crop right after planting – the butterfly cannot reach the leaves at all.
- Mixed culture: plant tomatoes, celery, sage, thyme and marigolds among the cabbage – their scent irritates the butterflies.
- Check regularly: search the leaf undersides weekly and simply wipe off egg clusters.
- Encourage beneficials: parasitic wasps, birds and lacewings keep the caterpillars in check.
Controlling caterpillars naturally
- Collecting: pick off caterpillars and egg clusters on every walk through the bed – often enough on its own for small plots.
- Bacillus thuringiensis: a biological product (Bt) based on a soil bacterium that acts specifically against caterpillars and spares beneficial insects.
- Encourage rather than spray: parasitic wasps parasitise the caterpillars, tits feed them to their young – a nest box near the bed helps.
- Rock dust: dusted onto the leaves it makes feeding harder for the caterpillars.
Tip
Put the net on right at planting and make sure it closes well at the edges – otherwise the butterflies slip underneath and lay their eggs directly on the protected crop.
Caution
Avoid chemical insecticides on cabbage – they contaminate the vegetables and kill the parasitic wasps that would otherwise do the work for you.
Frequently asked questions
Can I still eat affected cabbage?
You can remove lightly nibbled outer leaves; the inside is edible. Heads heavily soiled with droppings are better discarded.
When is the risk greatest?
From May to September in several generations – the butterflies are especially active on warm, sunny days.
Strong young plants grow out of the sensitive phase faster. We raise our cabbage seedlings to be robust – a good start to a healthy harvest.