Plant Doctor: Apprehensive About Apple

Q: I HAVE a three year-old ‘Golden Delicious’ apple tree. Recently I noticed lesions on some of the small branches. Is this canker? If so what can I do about it and will my other young apple tree become infected? D Challis, Waitakere.

A: THE lesions on the twig you sent are typical of the damage European canker inflicts on apples. It is a fungal disease common on many apple cultivars, and sometimes pears, in wet-climate parts of the country, such as Auckland, Waikato, Taranaki and Nelson. In dry regions, like Wairarapa, Marlborough, Canterbury and Otago, it is virtually unknown. The disease gets into the tree through cuts in the bark, particularly small leaf scars left when the leaves drop in autumn, and pruning wounds. Once infection takes hold the disease grows slowly inside the branch tissue causing the lesions that untreated can eventually kill off whole branches. You’ll probably never get rid of the disease but in the home garden there are several things you can do to keep damage to a minimum.

Prune out any infected areas as soon as you see them – don’t wait until winter. Treat all cut surfaces with pruning paste containing a fungicide, such as Bacseal. Spray regularly with a copper fungicide, like copper oxychloride, especially in autumn at leaf fall. There are also reports that copper sprays around the finish of flowering (petal fall) in spring can also help reduce incidence of the disease.

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