Much like cedar-apple rust, this is a fungal disorder that travels between two host plants - true firs (Abies species) and the vacciniums (blueberries and cranberries can also be infected). The best way to control is to remove the host fir species.

Otherwise, you can just prune out the infected portions, being sure to sterilize pruners after each cut. It really does not affect the health of the plants and is primarily cosmetic in nature.

https://pnwhandbooks.org/plantdisease/host-disease/huckleberry-vaccinium-spp-witches-broom-rust