In a rare 1969 epidemic, spruce cone rust caused by Chrysomyxa pirolata infected 40–100 percent of trees and 20–67 percent of cones on riparian Colorado blue spruce on plots located in a 2200–2400 m elevational zone in Huntington Canyon of central Utah. Uredinial and telial sporulation on Pyrola spp. began in mid-June, a time closely correlated with opening of pistillate spruce cones. Come phenology and host habitat, as influenced by elevation, are apparently important factors in the restricted niche of the cone rust fungus in Utah. Several preceding consecutive years with extended periods of spring and fall moisture were associated with occurrence of the epidemic, although no cause-and-effect relationship was established. Weather records indicate that these events are infrequent in this climatic zone, and there was no detectable recurrence of cone rust for at least 9 years following 1969. Outwardly normal seeds developed in diseased cones, but seed germinability was reduced by 25 percent. Aecial spore masses between cone scales, cone resinosis, and distortion of cone scales prevented seed dispersal to the extent that the seed crop was effectually destroyed.
Nelson, David L. and Krebill, Richard G.
"Occurrence and effect of Chrysomyxa pirolata cone rust on Picea pungens in Utah,"
Great Basin Naturalist: Vol. 42
, Article 11.
Available at: http://scholarsarchive.byu.edu/gbn/vol42/iss2/11