Cankers are localized dead areas of bark in trees and shrubs caused by fungi and bacterial infection. Canker pathogens can cause branches and twigs to die or be disfigured, and larger trunk cankers can even kill an entire tree in a very short time. Canker pathogens are among the most destructive tree diseases and include chestnut blight, butternut (white walnut) canker and dogwood anthracnose.

Chestnut blight canker form when a canker pathogen is able to penetrate the outer layer of bark usually through broken twigs, pruning cuts, mower damage, insect injury, hail damage or other injuries the tree may receive. Once the pathogen is in past the outer bark, they colonize other bark tissues weakening the infection point and reducing the heartiness of the tree, resulting in decay or tree death. Once canker is past the outer bark it moves into the inner bark choking off nutrients and starving entire portions of the tree.

Canker symptoms may look a little different depending on the type of canker and the species of tree. On thin barked trees cankers appear as sharply defined, slightly sunken depressed areas, which cause the bark in the affected areas to turn shades of red brown or black and sometimes have a foul-smelling sap. Symptoms on trees with thicker or rougher bark are a little harder to see, sometimes requiring careful shaving off of the outer bark with a knife. Some of the visible signs to look for in this case are spore producing structures on the surface of dead bark and can appear as black pepper-like spots or small bright red coral-like clusters.

Trees are especially susceptible to canker when there is drastic weather change. As there are many different types of canker and different methods of treatment the best course of action is to call a certified arborist to come out and examine your tree to recommend the best course of action.

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