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Disease Note

Spruce Needle Rust Epidemic in Alaska Caused by Chrysomyxa ledicola. J. H. McBeath, Agricultural and Forestry Experiment Station, University of Alaska, Fairbanks 99701.  Plant Disease 70:801, 1986.  Accepted for publication 16 April 1986.  Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-801d.

In the summer of 1985, an outbreak of needle rust (Chrysomyxa ledicola Lagerh.) occurred on spruce (Picea spp.) in the Big Delta and Tanana Loop areas of interior Alaska.  Approximately 130,000 ha of severely diseased spruce trees, predominantly white spruce (P. glauca (Moench) Voss), were observed in aerial and ground surveys.  Clusters of heavily affected spruce trees were also observed in the Fairbanks vicinity.  White spruce was found to be the most susceptible of all spruce species.  Weather in June was cool and rainy.  In early July, small yellow lesions appeared on young needles; spermogonia and aecia formed in the stomatal region in mid- and late July, respectively.  Diseased needles later turned brown, shriveled, and dropped from the branches in late fall.  The one-celled aeciospores were reddish orange, oval or elliptic, and covered with annulated processes.  Spruce needle rust was identified as C. ledicola on the basis of size and morphology of aeciospores.  The uredia and telia of C. ledicola have been found on the alternate hosts wild rosemary (Ledum decumbens (Ait.) Lodd and L. groenlandicum Oeder).  In white spruce stands close to high populations of L. decumbens and L. groenlandicum, the incidence of needle rust was over 90%.

Reference: W. G. Ziller. Can. For. Serv. Publ. 1329, 1974.