White butterfly

Active from spring right through to late autumn, September to May, with the worst pressure in summer.

The white butterfly, or cabbage white, is the number one brassica pest in New Zealand gardens. The velvety green caterpillars chew large ragged holes in cabbages, broccoli, kale and other brassicas and bore into the hearts, fouling them with droppings.

How to identify

• White butterflies with one or two black wing spots fluttering over the patch
• Single yellow bullet-shaped eggs laid on leaf undersides
• Velvety green caterpillars up to 30mm, often along leaf veins
• Large ragged holes in leaves and caterpillars tunnelled into hearts
• Dark green-brown droppings scattered over the leaves

How to prevent

• Cover brassicas with fine insect mesh from planting to block egg-laying
• Check leaf undersides weekly and rub off the small yellow eggs
• Plant butterfly-decoy crops or white eggshell halves, which can deter egg-laying females
• Clear spent brassicas and weedy nasturtiums and cresses that host them
• Rotate brassicas so pressure does not build in one bed

How to control organically

• Hand-pick caterpillars, checking veins and the centre of the plant
• Spray a Btk product such as Yates Success or Kiwicare caterpillar spray, which targets only caterpillars and spares bees
• Mix the spray fresh, apply late in the day and reapply every 7 to 10 days and after rain
• Use a neem-based spray as an alternative to deter feeding and egg-laying
• Encourage and protect parasitic wasps and birds that prey on caterpillars