European Canker (Nectria Canker)

European Canker (Nectria Canker)

Causal agent: Nectria galligena

European canker is severe in coastal orchards, and has been a problem in some interior orchards in high rainfall areas. While not a common problem in the dry climate of the Okanagan/Similkameen valleys, the disease has been introduced to some orchards on nursery stock grown in wet climate areas. At the time of purchase infected nursery stock may have no obvious symptoms of canker, but cankers develop during the first year after planting. Natural spread of European canker in Okanagan orchards is possible, but the disease is less aggressive in dry climate areas.

Symptoms

The first sign of canker is a reddish-brown spot around a leaf scar, spur or pruning wound, usually in late spring or early summer. The canker develops quickly with ring shaped cracks forming in the bark. If the canker girdles the trunk or branch, shoots above the canker die. The canker usually stops growing after one year. A ridge or collar of healthy tissue walls off the canker. Young cankers produce small, whitish fruiting bodies. Older cankers may produce orange-red fruiting bodies.

European canker can sometimes be confused with anthracnose canker.

European canker European canker on apple

Life Cycle

Spores from new cankers are spread primarily by rain or overhead irrigation. New infections are thought to occur mainly in the autumn through leaf scars, with symptoms appearing the following spring. Older cankers produce airborne spores (ascospores) that can initiate new infections at a distance from the source. The airborne spores function mainly to initiate new infections, while the water-borne spores serve to intensify the disease in trees that are already infected.

Cultural Control

Prune out diseased wood. On young trees this often means pulling out the tree or pruning it back severely.
Scrape away the diseased rough bark to prevent the spore fruiting bodies from developing. Only attempt this if the canker is not seriously girdling the trunk or limb.
Nursery trees should be examined carefully for symptoms of the disease. Trees with cankers should be returned to the nursery for replacement or discarded.

Chemical Control

There are no fungicides registered for control of European canker in Canada.

Fungicides applied for other diseases such as apple scab may help to reduce the numbers of new infections. Copper fungicides such as Bordeaux mixture are recommended in some wet climate areas.

February 2004

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