Plant Doctor Archive

Cypress hedge dying off

SEVERAL years ago we planted a Leyland cypress hedge along one boundary of our block of land and it has grown really well. But now I notice a few branches here and there are turning yellow and dying off. Can you help?

IT SOUNDS like your hedge has become infected with cypress canker, a fungal disease that attacks a fairly limited range of Cupressus species as well as some close relatives, such as the hybrid Leyland cypress. If you look closely at dying shoots you might see brown powdery specks which are the fungal fruiting bodies and there may also be sticky resin oozing from the bark. If the disease gets into the main trunk it can eventually kill the whole tree.

Unfortunately there are no readily available fungicides that claim to cure cypress canker, but many gardeners and small block owners say they have achieved reasonable control by spraying with copper fungicides, such as copper oxychloride.

Spraying a large hedge two or three times a year can be a daunting, if not almost impossible, task to do well, but there is still hope. If your hedge is growing strongly and has no other complications to cope with, such as poor drainage, it could survive and serve its purpose for many years to come, especially if you cut out affected branches as soon as you spot them.

The disease gets into trees through splits in the bark or pruning cuts, particularly when growth is slow such as during winter, so try to prune your hedge in spring or summer when cuts will heal over quickly. Ideally, apply a copper spray as soon as possible after pruning or trimming in an attempt to prevent disease spores gaining entry through the cut surfaces.

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