Plant Doctor Archive

Warding off scale

OUR golden totara is covered in tiny white insects. The tree is probably 20 or more years old and I've not noticed the problem before. Are they harmful and, if so, what can we do about them? It would be difficult to spray such a large tree.

THE sample you sent had a quite a severe infestation of scale insects, which feed by sucking sap. Scale can cause quite serious growth problems to some plants but totara are tough and should be able to tolerate a few patches of scale. It's likely the scale are in scattered populations, probably mostly in the lower, sheltered parts of the tree and that the upper branches, which are more exposed to the elements, will not be affected.

An easy way to reduce a scale population like this is to lightly prune back the infested shoots. Don't cut them hard back, just remove those shoots with scale and dispose of them in the rubbish or burn them.

Alternatively, or as well as pruning, you could apply an oil spray, which kills by covering scales' skin with oil, blocking the breathing pores. Spraying oils like Eco Oil, Clear White Oil, and Conqueror are safe and easy to use. Ideally, spray on a cloudy day and try to avoid getting spray on nearby leafy plants as the oil can damage tender new spring foliage. Ensure thorough coverage, especially under the leaves where most scale feeds.

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