Re: Pearleaf Blister Mites
The site you link suggests doing the spray after harvest.
My sister had them pretty bad on her pear tree last year as well. I was planning to try to apply neem oil to it this spring but didn't get to it and there weren't many rain breaks.
It sounds like it may not have helped anyway.
From reading this winter I was of the impression that once the blisters are forming it is too late. They are already safely under the surface.
my sisters tree last spring