Tree cankers develop on branches and stems as a result of a fungal infection that enters through a wound. 

What are the Risks?Cankers on Poplar tree

Cankers can result in branch death, and in some cases, the eventual weakening and death of the entire tree. Cankers can be difficult to diagnose and often appear in the late summer or early fall.

What to Look For

Depending on the type of tree and fungus, cankers can vary in size, shape, and colour, making them difficult to identify.

Canker of spruce affects spruce, tamarack larch, and white pine trees. Cytospora cankers can affect many tree species, including poplar, balsam, and aspen.


With an infected tree, it is best to remove all affected areas by pruning the dead and dying branches. Use clean pruning shears and disinfect cutting tools after use to prevent further spread of the fungus.

You can protect your trees by keeping them as healthy as possible. This includes:

  • Regular aeration
  • Balanced fertilization
  • Watering in times of drought