Canker is a general term for a symptom of a variety of tree diseases.  Cankers are sunken, discolored areas of dead tissue on branches that may ooze sap.  If it progresses far enough to encircle the branch (or trunk), the portion of the tree above it will die.

In Grande Prairie, canker diseases commonly affect:

  • Cherries and plums - bacterial canker
  • Russian olive and sea buckthorn - phomopsis canker
  • Trembling aspen - hypoxylon and black canker
  • Elm - Valsa canker
  • Apple - apple canker, nectria, and fireblight
  • Mountain ash - nectria, cytospora and fireblight
  • Spruce - cytospora


Preventing unnecessary bark wounding is key to stopping canker disease, as they preferentially enter the tree through wounds:

  • Keep mowers and trimmers away from the trunk of the tree. 
  • Prune during the dormant season.
  • Avoid flush cuts (these damage the bark collar that closes the wound, and leave the wound open to infection much longer).
  • Avoid unnecessary pruning. 
  • Do not use pruning paint to cover wounds.  This impedes healing and keeps the wound open longer.

Keep your trees healthy, as stressed trees cannot fight pathogens as well.  Water them during dry spells and watch for insect attacks.

Control of cankers is limited to removal.  There are few, if any, registered pesticides to aid in canker control once it's infected the tree.  Cut out the disease at least 12 inches (30cm) below the canker, preferably to the next branch, and destroy it immediately by burning or sending it to the landfill.



Bacterial blight canker on Toka plum tree
Canker on trembling aspen caused by trimmer damage. Thin-barked trees such as aspen, cherry and mountain ash must be protected from trunk damage to lower the chance of canker infection.
Canker on trembling aspen caused by a branch ripped off (visible at bottom of picture). Note dieback of branches as the trunk is being girdled.