A Technical Report from The Bartlett Tree Research Laboratories 396
Weir’s cushion rust of spruce, also called spruce needle rust, is caused by the fungus Chrysomyxa weirii. This fungus is native to the western United States, but is now found throughout North America from Canada south through the southern Appalachian Mountains. The disease rarely kills spruce, but can seriously defoliate and disfigure trees creating a problem for nurseries, landscapes, and Christmas tree growers. Colorado blue spruce is the most commonly and seriously affected, but all spruce species are susceptible.