Visually, cankers are deformed portions of the tree or shrub such as dead branches, discolored (usually darker) bark, sunken or swollen bark. On pines, the cankers may produce a sticky whitish sap which dries.
Cankers are dead, deformed areas on branches, twigs, or trunk of the tree, located under the bark. Cankers may be caused by disease, fungus, bacteria or mechanical injury (such as damage from a weed wacker or other mechanics that damage the exterior of the plant) to the tree. Cankers may cause dieback and can be difficult to control, they can also invite more insects and disease activity because the overall health of the tree is in declined.