Sorbus sargentiana

[brianw]

I planted a full standard of this Sorbus 3 years ago and noticed recently damage ~18" up the main stem. It is a "black" hole large enough to get 2 finger joints in with apparently wider damage under the bark around it. The stem is no thicker than  ~4 cms so will considerably weaken the stem even if it gets no larger. It was under a tree guard or I would have noticed it earlier. At present I have just sprayed a lot of sulphur into it. Any suggestions?
There is a single shoot a few inches below it but I am reluctant to just cut the whole stem off at present as it is 9 feet or so tall, and it will never look much if I do, at least in my lifetime. ;-(

[GordonT]

I am not sure, but from the sounds of it, your tree may have been attacked by a borer. In eastern North America we have to look out for flathead appletree borers, and invasive longhorn beetles in select areas where the latter have established a foothold. I am not sure what you ought to do now, but the extended area of damage under the bark would suggest larvae have been tunneling.

[brianw]

I suspect I have apple canker, after much searching. Sorbus are susceptible to it apparently.
So I need to clean it up and protect it if I want to attempt to save the tree. Not looking forward to that at this time of the year. Wish I had seen it sooner. Lots on line about filling the hole, or not, as the current feeling is. I think it may be too much of a reservoir if I don't fill it, at least partially. One of the builders foams seems most appropriate now; assuming there is enough strength left in the stem/trunk. I have one or these portable rotary grinding wheel gadgets. Maybe I can persuade my dentist to help out ;-)