Here are some five year old Sumner and Elliots that have sunken, cracked areas in the bark that appear pulled away from the wood. This is the result of Botryosphaeria canker or “Bot Canker.” This is a problem that is usually not noticed until it becomes severe. UGA Extension Horticulturalist Dr. Lenny Wells says, “Bot canker” is caused by a fungus which can infect the tree through wounds like limb breakage, pruning sites, or small cracks. The infected wood may appear black while the bark surrounding the wound site appears grey-white in color. The problem is easily taken care of when caught in time but can lead to serious problems when left un-checked.
Botryosphaeria fungi may initially colonize dead tissue and move downward on the branch or trunk into healthy bark and sapwood. Spread occurs through air movement or splash dispersal of spores, and can also occur through use of contaminated pruning tools.”
For trees that are not too far gone, it is recommended to use white latex paint on the infected area. This reflects the sunlight into the infected area which worsens the canker. Below is a photo of a tree painted.