Question
My Choke Cherry has developed wide thick black growth on many of its
branches.  The branches affected have narrowed near the trunk.  Though there
were many, I cut all the sick branches off.  I am clueless as to what this is or
how to treat.

Answer
If the black areas are sort of like charcoal and hard, then I would say the tree has black knot, which is a fungal disease.  There are fungicides to help prevent this.  Pruning off the affected branches is one of the management tools that you have already started.  Check google for a list of fungicides to use.  Good Luck.