Tree Canker Disease

Tree Canker

Rosser1954 / Wikimedia Commons / CC BY-SA 3.0

The term " canker" is used to describe a killed area or blister on the bark, a branch or the trunk of an infected tree. The Morton Arboretum describes it as a canker that is "usually oval to elongate, but can vary in size and shape." Cankers will often appear as a swelling surrounding a sunken lesion on the bark of trunks and branches.

The canker-causing pathogens like fungi and bacteria commonly invade wounded or injured bark tissues to form a canker. They subsequently produce reproductive structures called fruiting bodies and can spread. Dozens of species of fungi cause canker disease.


Cankers are caused by a number of factors including biotic fungi and bacteria or by abiotic and nonliving conditions to include excessive low or high temperature, hail and other natural and mechanical tree damage. A combination of these attacks is potentially the most successful process in causing a tree to develop a canker.

The fungi that cause cankers are always around and naturally inhabit the bark surface of a tree. They look for the opportunity to gain entrance through natural or man-made wounds and usually have the best chance to cause canker disease when the tree is under stress. Stressors that cause cankers include:

  • exposure to extremely high or low temperatures
  • flooding and drought
  • summer or winter sunscald, hail, high winds
  • nutritional imbalances and soil compaction
  • mechanical injuries (lawn mower, vehicles) and animal damage
  • pruning wounds
  • root rot and insect borers
  • improper planting


Preventing cankers means growing vigorous trees that can fight off the entrance of pathogens into the bark by using a good tree management program. You must be faithful to your tree by using correct pruning methods, taking care not to over-fertilize and prevent defoliation of your tree by disease and insects.

Wounds are essential for most canker infections to take hold and spread, so avoid wounds, especially where active spore-spreading cankers are present. Make sure that your tree has adequate water and avoid mechanical injury to roots and trunk.

When planting a new tree: Plant your tree on a good site, use vigorous planting stock, fertilize trees to promote growth and control weeds for several years after planting. Landscape trees will benefit by deep watering or trickle irrigation, especially during dry summer months. Also maintain good drainage.


Canker diseases can be controlled if diagnosed early and action is taken. To control canker disease on trees, cut off the affected branch or limb using proper pruning methods.


Do not cut into trunk cankers as it may renew fungal activity and increase damage.

If a large canker is on the main trunk, the tree may ultimately need to be replaced. Still remember that when a trunk canker develops, the tree may begin to compartmentalize off the area by sealing wood cells off around the canker. You may be able to extend the life of the tree by just leaving it alone. There are no effective chemicals are available to control the fungi that cause canker disease.