Canker Disease in Trees

Canker disease mostly occurs on ornamental woody plants, forest trees, and some fruit trees such as apple, peach, and pear, etc. It causes dieback of twigs and branches, reduces tree growth, affects lumber quality, and causes significant yield losses on fruit trees. Sometimes, it kills the entire tree if the canker girdles the trunk of a tree.

Furthermore, canker disease on a tree will be seen as an inverted blister on the bark of the tree which, during some time of the year, may ooze sap. A canker forms on branches or trunks of trees. Fungi, very small organisms that produce spores and mold-like material, cause most canker diseases.

Leaves of a tree affected by these fungi begin to turn yellow and may drop to the ground. Some limbs may not develop new leaves in the spring. In severe cases, trees may die if canker disease isn't treated for a few years.

Most canker-causing fungi overwinter in dead or infected bark tissue in which fungal fruiting bodies, spores or mycelia are present. In the spring, fungal spores are transmitted by wind, rain, water, or pruning tools to other trees or other parts of the same tree. If spores reach a stressed or injured tree and find desirable infection sites (usually those injured spots or natural holes on the bark), they germinate immediately and then penetrate into the bark tissue.

The first step to detect a canker disease is to look for symptoms. The most common symptom caused by canker disease is dieback. Check the tree to see if any twigs or branches are dead or not growing well (for example, buds are not open, or leaves are dead, etc.).

As most of the canker fungi are opportunistic and like to attack those weakened trees, keeping tree’s growth vigor is very critical to lower the chance of infection. Avoiding wounding or severe pruning also will reduce opportunities for fungi to attack. Removing cankers and treating with a disinfectant will prevent further expanding of the canker area.