Thank you for sending the image outside of this system. Fungal growth is an indicator that some sort of rot is going on, in the trunk, base or root system. i was not able to identify the exact kind of fungus your hackberry has, but do suspect that it has been ongoing for some time. You can use a probe to determine how soft the area is and the extent of the decay to monitor the problem. Once a tree begins to decay, it is very difficult(impossible0 to reverse the problem. Exposure to good air movement and sunlight can help dry the area out, potentially lessening the spread.
