Plant Doctor Archive

Caterpillars on kōwhai

Question I HAVE a dwarf kōwhai, ‘Dragons Gold’, which was devastated by caterpillars in summer. It was in a tub, but I have since planted it in the garden and it seems to have recovered enough to produce a covering of leaves, but only about half a dozen flowers. Should I give it a feed? If so, is a slow-release fertiliser the best? Also, what is the best spray to use to prevent another caterpillar attack? I have used Neem oil in the past.

Answer  KŌWHAI don’t generally require much in the way of feeding, so in reasonable garden soil a general fertiliser, whether slow-release or not, should be fine. Don’t be tempted to apply lots of fertiliser, as you’ll probably only encourage lush growth at the expense of flowers.

What’s likely to also have a very beneficial effect is applying a good layer of mulch to conserve soil moisture over summer, as well as an occasional watering in dry periods.

Neem oil should help control kōwhai moth caterpillars, but you’ll need to spray at the right time. Check your plants regularly through summer and spray as soon as you spot the first few caterpillars — while they’re still small and haven’t had time to do much damage. You need to be vigilant, as they grow quickly and can sometimes strip a small tree in just a few days! One or two timely sprays will often be enough to control them.

Other products you could use include Success Naturalyte, one of the many pyrethrum-based products such as Garlic & Pyrethrum, and Derris Dust.

Weekend Gardener, Issue 178, 2005, Page 32