Rowan tree disease identification help plese

My Rowan tree has got a disease that I would like some help in identifying if possible?  I think that it is probably leaf spot or fire blight but I am not sure.  The leaves have been developing brown spots and some defoliation has started.  The bark does not seem particularly bad and I cannot see any signs of honey fungus when I cut a little bark away. I have cut away a couple of branches and there is some dark stains inside the branches.  If it is leaf spot does anyone know how to tell if this is caused by bacteria or fungus? I would like to treat the tree if it can be saved but I need to identify the exact problem first.