It is difficult to diagnose the tree from a photo, but I believe the tree has Botryosphaeria canker. The fungus kills bark and phloem tissue and infections may occur randomly throughout the tree. The cankers appear as sunken areas of bark that may be surrounded by swollen edges (callus tissue) and covered with roughened bark that occasionally splits to expose the xylem. The cankers range in size from small, almost unnoticeable elliptical lesions, to large areas of blighted tissue. Branches with multiple cankers are girdled and killed causing leaves on the affected branch to turn reddish-brown, a symptom known as "flagging." Entire trees may be killed if the cankers move from branches into the main stem.

Maintaining healthy trees is the best defense against Botryosphaeria canker since vigorously growing trees can resist infection. Proper site selection, planting, and aftercare are all essential to avoid loss of branches or entire trees to this fungus. It is particularly important to provide water throughout periods of extended drought. Should trees become infected, it is essential to remove cankered branches promptly upon detection to reduce spread of the disease within the tree or to nearby trees. Pruning should be done during dry weather and cuts made at least 6 - 8" below infected tissue. Pruning tools should be sterilized between cuts using denatured alcohol to prevent the tools from becoming vectors of the disease. Fungicide applications have not proven to be effective in controlling this cankering disease.