Cankers are dead areas of bark, caused by fungi and bacterial infection. Cankers can be found on branches as well as on tree trunks. Such an infection can cause a draw back in annual branch or twig growth. Yet on the stem it can create visually interesting formations which can be deadly to a tree. Organisms which cause a canker formation can enter and infect the bark through wounds. These wounds could be caused by broken branches, or insects which have caused an injury. When canker pathogens pass through the outer bark barrier, they can colonize other bark tissue. Cankers can enhance wood decay, and cause branch breakage or tree death (Tisserat 2004).
Fig 12. Canker on a tree trunk. Picture taken from:
Ned A. Tisserat, 2004 Canker Diseases of Trees, Kansas State University Agricultural Experiment Station and Cooperative Ex tension Service,