Canker (Latin name varies depending on species)

 
Plants/trees affected

Ash, Beech, Hawthorn, Poplar, Sorbus, Willow, Roses and Fruit Trees such as Apples, Pears, Cherries, Nectarines, Peaches and Plums.

 

Symptoms

There are two kinds of canker one cause by fungus and the other by bacteria.  The fungal canker becomes noticeable in autumn as a swelling of the bark, often where there is a damaged bud or where a pruning wound has occurred. The central part of the swelling begins to die back and the bark flakes off leaving a sunken discoloured area. In summer, white fungus grows on the diseased bark, which turns to a red fungus in winter.  The symptoms of bacterial canker are small depressions or areas of damaged bark which get bigger in spring and ooze and an orange/yellow sticky gum. Leaves of affected branches can also develop brown spots surrounded by a yellow halo, the brown spots fall out to leave a ‘shot hole’ effect on the leaf.

Causes

Fungal canker is caused by spores penetrating wounds or weak spots on the tree such as those caused by pruning or frost damage. The fungus spores over winter on dead or infected bark and are then transferred by wind, rain or pruning tools.  Spores germinate quickly penetrating and killing the bark cells on the tree but then reproduce and easily spread to other vulnerable or weakened species.  Bacterial canker is from bacteria often found on the surface of plants like Pseudomonas syringae pv. Morsprunorum. This infects the plant through leaf scars or wounds, goes on to form a canker and houses the bacteria over winter. The bacteria are most active in periods of high moisture and low temperatures and can be spread by splashing rain.

 

Prevention

As both canker fungi and bacteria like to attack weakened trees keeping the tree in good health is the best form of defense.  Ensuring good drainage and mulching in spring with good farmyard manure or well rotted organic material should help improve the plants general well being. Trees should be pruned during dry spells in June-Aug taking care not to cause pruning wounds. A copper based fungicide (eg Bordeaux mixture like Murphy Traditional Fungicide) can be used to protect leaf scars and bark wounds.  Refer to manufactures instructions but this is best applied in Autumn (Aug-Oct).

Also when pruning out canker infected areas, it is important to wipe the pruning tools with disinfectant between every cut to avoid spreading the disease.

Treatment