Hi Parker, thanks for posting this question to the MyWoodlot forum! I am not an expert in this area, but I can provide you with some helpful resources. My advice would be to first determine that it is in fact Rhizosphaeara that is causing needles to drop. These extension articles discuss possible reasons for blue spruce needle loss, as well as treatment options for Rhizosphaeara:
New Mexico State University publication, Rhizosphaera Needle Cast Disease of Blue Spruce - has a good paragraph on Disease Management: https://aces.nmsu.edu/pubs/_h/H163/welcome.html
Purdue University publication, Why Spruce Trees Lose Their Needles - explains a telltale sign of Rhizosphaera, tiny black dots arranged in rows on infected needles: https://extension.purdue.edu/article/29053
Michigan State University publication, What's going on with blue spruce? - https://www.canr.msu.edu/news/whats_going_on_with_blue_spruce
Iowa State University article - Common Diseases of Blue Spruce
I hope you find these to be helpful. I would be interested to learn about your course of action.