What is killing this hawthorn?

[Javaman4373]

I found a soft spot on the bark of this hawthorn and probed it and discovered dark rotten cambium underneath. I debrided it down to the sap wood and followed it where ever it went and found a large area on the trunk that seems to girdle the whole thing to the point that I am surprised there was leaves and live buds above the affected area. I am guessing some sort of fungus and inquire here to see if anyone recognizes this problem. I assume the tree is doomed.

 

[Potawatomi13]

The close up seems to show two possible borer holes. If the tree dies above the low branch it will still make an interesting tree. Treat with systemic and topical insecticide, leave alone till next year and see if anything grows and if it lives treat again and continuing growing it.

 

[Shibui]

If the trunk is completely girdled - no live connection between roots and top - then the top will die. It's probably making a last ditch attempt using whatever stores of water and energy are in the trunk itself.
If there's even a small strip of cambium connecting base to top it may survive, provided whatever has affected the bark does not continue to spread.

My first thought was also borers but the damage does not usually spread as far as this.
Physical damage is also possible but unusual to spread all round the trunk.
Other wise not sure what has occurred.

 

[Javaman4373]

Thanks for the comments. I did treat with a systemic insecticide and while I was at it, I treated my other hawthorns and tamaracks. I did find what looked like a short borer track, but it didn't seem to account for all the damage. Since the top was fully girdled and doomed, I made an air layer where the cambium was still live. Wrong tiime of year and probably won't work, but I have nothing to lose at this point. I wonder if the exposed sap wood should be coated with something to protect it. The tree is going to be in an unheated garage over the winter.