Weekend gardening

Pest control Is it possible to rid your garden of voracious cabbage whites?

Why even bother to start your winter veges now when the voracious white cabbage butterflies are certain to decimate your young crop?

Well, for one thing, you’ll be taking advantage of the longer daylight hours and warmer weather to make your seedlings strong before planting out.

But many gardeners question the logic of the early planting of winter veges because of the white butterfly, their caterpillars and eggs.

And while you may be keeping the seedlings in trays inside, away from the whites, or undercover, white cabbage butterflies still have a way of getting at your seedlings, says regular NZ Gardener contributor Kath Irvine. She has written extensively about their control and says her initial method was squishing the caterpillars and flicking the eggs.

But as her family and garden grew, she realised the prolific pest needed something more than digital control and turned to Bt (Bacillus thuringiensis) spray, an effective and easy means of control.

You have to spray for total foliage coverage and in a day or two, all the caterpillars will be brown and dangling like baubles, beneath the leaves, she says. However, she later changed her mind about sprays and stopped using Bt because of her concern for the diversity of her garden, and especially its effect on other insects.

Kath suggests checking seedlings for the creamy bullet-shaped eggs or green caterpillars regularly, even when you are using mesh.

Kath also encourages natural predators in her open garden, such as parasitic wasps and even paper wasps, by growing lots of companion plants for a year-round supply of nectar and pollen, as these will target the caterpillars. (But be aware these may also target monarchs.)

The other option, of course, is to wait for late autumn, early winter when the cold weather will see the butterflies gone.