Re: When to prune Norway Spruce in lower Michigan
The same pruning practices should be used to control the needlecast. (Disinfect using 70% isopropyl alcohol.) Also you should try to improve the air circulation around the blue spruce by mowing underneath and if possible cutting down bushes or other trees that are crowding the infected spruce. Michigan State has some detailed information about the timing of fungicide applications here that may help you.