Cankers

A canker is a sunken wound in bark. This wound is an open sore filled with dead plant tissue. Okay, so it’s not the prettiest thing we’ve discussed. But it is important to know where cankers come from, how to prevent them, and how to treat them. Your trees will thank you!

Butternut tree infected with fatal canker disease (Mike Ostry, US Forest Service) CC BY 3.0 us Public Domain

Canker causes and identification

Some cankers are obvious and some are not. Both fungal and bacterial microorganisms infect the cambium layer of trees and shrubs, creating cankers. They are very slow to heal and often do not heal at all. If the wound travels laterally, the sap found in the xylem and phloem cannot move, and the branch dies.


Foliage on infected branches often turns yellow or brown and wilts. Cankers can encircle (girdle) and kill limbs or an entire tree. Common canker diseases include Eutypa dieback, pitch canker, fire blight, Fusarium wilt, chestnut blight, pine blister rust, anthracnose diseases, and sudden oak death.

Healthy bark (left) protects the tree. Cankers (right) allow problems to enter. (Hannahzd3) CC BY-SA 4.0

How to prevent cankers

The best prevention method is planting resistant cultivars. Also, installing plants best suited to the local microclimate helps them be strong enough to fight off pests and diseases. Good cultural care, such as proper pruning, watering, and feeding, will also help prevent infection. Remove dead and diseased limbs right away. Avoid heavy feeding since that may stimulate vulnerable new growth. Sunburn and overwatering can both make plants susceptible to various canker diseases. Many healthy trees have these pathogens present, but unhealthy trees are more likely to become sick, just like us.Some cankers are obvious and some are not. They are caused by fungal and bacterial microorganisms that infect the cambium layer of trees and shrubs. Cankers are very slow to heal and often do not heal at all. If the wound travels laterally, the sap found in the xylem and phloem cannot move and the branch dies.


Foliage on infected branches often turns yellow or brown and wilts. Cankers can encircle (girdle) and kill limbs or an entire tree. Common canker diseases include: Eutypa dieback, pitch canker, fire blight, Fusarium wilt, chestnut blight, pine blister rust, anthracnose diseases and sudden oak death.

Canker on a birch tree (MarkusHagenlocher) CC BY-SA 3.0

Treating cankers

Once a fungal disease has taken hold, getting rid of it can be difficult. Most fungicide treatments are ineffective against fungal cankers, and the same is true for bacterial infections. Maintaining healthy plants allows them to fight for themselves.