Plant Doctor Archive

 I WAS horrified to find my 10-year-old kōwhai had been attacked by voracious caterpillars. We live on a farm where there are no other kōwhai trees around and I have never had this happen before. They did not like the shower of fly spray I gave them, but is there anything I can do to prevent my poor tree being attacked again?

  KŌWHAI moth caterpillars regularly strip the foliage from both young and mature kōwhai. Damage happens most often from summer through to autumn and in most cases the tree suffers very little permanent damage. A healthy tree soon throws out a full set of new leaves, so often there’s little need to try to control them. Most times you don’t realise the caterpillars are there until the damage is so bad it’s too late to do anything about it.

If you do notice a few caterpillars on the tree, you could spray with the low-toxicity insecticide Success Naturalyte, which controls almost all types of caterpillars. It can take several days for the caterpillars to die following spraying with this product, so don’t panic if nothing happens right away.

A trick I learned recently is that if the tree is small enough for you to give it a good shake, a lot of the caterpillars will drop off on to a sheet laid on the ground beneath and you can dispose of them.

Also worth remembering is that quite a few parasitic wasps and other bugs feed on the kōwhai moth caterpillars, so if you can maintain a healthy insect population in your area, the kōwhai tree may be less likely to be badly affected.

Weekend Gardener, Issue 196, 2006, Page 39

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