Plant Doctor Archive

Bronze beetle damage

I HAVE a 40-year-old pohutukawa grown as a bonsai, which I prune hard. This year the new growth is full of holes. I have a number of other pohutukawas in different parts of the garden that are all fine.

THE damage on the samples you sent is typical of that caused by the native bronze beetle. The adult beetle is around 5mm long and it chews holes in leaves but can also damage fruit and flowers of quite a range of plants. They can be quite hard to catch in the act of damaging plants, as they feed mostly at night underneath the leaves, and if disturbed will jump off and hide in the soil. Generally, by the time you discover the telltale holes, the beetle has moved on and it's too late to take any action.

The larvae live in the soil, feeding mainly on the roots of grass and clover. They pupate and emerge as adults from around November to January, which is often when much of the damage is done. Perhaps the new growth on your bonsai pohutukawa was at a more tender stage than the others in your garden and so suffered more, but they have been known to cause quite severe damage to quite large specimens as well as fruit trees.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.