Chrysomyxa pirolata

The spruce cone rust, caused by the rust fungus Chrysomyxa pirolata Wint., affects spruces in 3 continents, including white spruce in Canada. Alternate hosts of the fungus are several species among 3 genera of wintergreen: Pyrola spp., Orthilia spp., and Moneses spp.. Diseased cones open prematurely and orange-yellow aeciospores are sometimes produced in such quantity as to color the forest floor and lake surfaces. Up to half of a cone crop can be affected, and most of the affected cones do not produce viable seed. Some localities commonly experience damage to 20% to 30% of cone crops, a factor to be considered in the siting of seed orchards.