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Cytospora canker

Cytospora canker - Cytospora canker on aspen, caused by <em>Valsa sordida</em>.
  • Latin name: Valsa sordida Nitschke
  • French name: Chancre cytosporéen
  • Division: Ascomycota
  • Class: Diaporthales
  • Synonym(s): Cytospora pulcherrima Dearn. and Hansbr.


Branch, Trunk, Annual shoot


Eastern Canada

Damage, symptoms and biology

We can observe a zone of dead bark, sunken and brown around the entry point, generally a wound or a dead twig. Under the bark, the wood is discoloured, wet and foul-smelling.  We can also see orange-coloured fructifications and sometimes orange-coloured tendrils (conidia) coming out of the bark.

This disease appears as sunken, dead areas of brown bark, around an entry point of infection, generally a wound or dead twig. Under the bark, the wood is discoloured and wet and has an unpleasant odour. Orange fruiting bodies and occasionally orange tendrils (conidia) protruding through the bark can also be seen. This disease is rarely a problem of economic importance in natural stands, but can cause serious damage in forest nurseries, young plantations, and in horticultural settings. The initial infection is followed by the death of part of the bark and rarely by the formation of a true canker. In humid weather, the spores of the fungus are released from the bark in the form of orange tendrils and are spread by rain, wind or animals.

In disease affects already weakened or stressed trees, and the fungus usually gains entry through a wound on the branches or trunk. After the infection is initiated, part of the bark dies and a true canker may form in rare cases

Other information

The disease causes greater damage in young trees. Some hybrid poplars are much more resistant than indigenous species.

Cytospora chrysosperma has been shown to inhabit healthy bark of aspen and beech, causing disease only in trees or branches of low vigour or when the hosts are stressed by drought, injury, sunscald, fire, or other pathological disorders. The presence of this disease generally indicates that the trees are under stress. Cytospora nivea (Hoffm.: Fr. Sacc.) and its teleomorph Leucostoma nivea (Hoffm.: Fr) Höhnel also cause similar damage in poplars. Other species of Valsa, including Valsa abietis Fr. (anamorph: C. abietis Sacc.) and V. pini (Alb. & Schw. ex Fr.) Fr. (anamorph: C. pini Desmaz.) are associated with cankers and dieback of conifers.

Canadian Forest Service Publications

Cytospora canker

Information on host(s)

Main host(s)

Balsam poplar, golden weeping willow, largetooth aspen, Lombardy poplar, trembling aspen, willow

Secondary host(s)

Apples, choke cherry, eastern cottonwood, elders, European white poplar, maple, mountain-ash, Norway maple, oaks, silver maple, sugar maple, water birch, white birch


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