Every Australian gardener with a veggie patch knows them: I’m talking about a grey-white butterfly with black dots on the upper surface of its forewings. Or, what really causes the damage – a velvety green caterpillar covered with fine short hairs.
Pieris rapae (the scientific name of cabbage white butterfly) is the most serious economic butterfly pest in Australia. In its caterpillar stage it munches its way through the foliage of all kinds of cabbages, cauliflower, broccoli, Brussel sprouts, radish, mustard, kale, and turnip, and can easily destroy an entire harvest.
Fortunately, there are a few things we can do to reduce the problem.
Cabbage white butterfly likes warm weather, and is most active in spring/early summer, and in autumn. If you regularly wrestle with these pests, it’s best to grow vegetables of the cabbage family during the cool season only. Sow in autumn, and by the time the butterfly hatches in late spring, your vegetables should be ready to harvest. Winter chill only enhances the flavour of cruciferous vegetables.
Some people swear by growing nasturtiums close by – the butterflies are so keen on nasturtium that it helps keep the pest burden on your vegetables down. Sage seems to repel cabbage white butterfly, and dill is attractive to parasitic wasps – that’s two herbs your kitchen should never be without anyway. And – as always – keep your garden weeded: shepherds purse and wild mustard are favourite breeding ground for cabbage white butterfly!
If you discover holes in your kale, it’s best to examine the underside of leaves. And if you do find yourself staring at green caterpillars, or the greenish-brown pellets of their excrement, it’s time for Beat A Bug. Obviously, treatment is more effective when caterpillars are small, so patrol your veggie patch every day when the butterfly is active, and repeat application regularly.
If the pest burden is really high, remove and destroy the infested crop, and start again. Netting your cabbage vegetables with a fine mesh may be the only solution in such a situation. It is a bit of work, but preventing access to your precious vegetables is still the most effective way to keep cabbage white butterfly out of your garden.
Birgit Daller is a horticulturist and garden designer, and the owner and creative head of Art of Green Landscapes & Design.