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Mountain Hemlock Is Occasional Host for Hemlock Dwarf Mistletoe in Alaska. Charles G. Shaw III, Research Plant Pathologist, Forestry Sciences Laboratory, Pacific Northwest Forest and Range Experiment Station, USDA Forest Service, Juneau, AK 99802. Plant Dis. 66:852-854. Accepted for publication 8 March 1982. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1982. DOI: 10.1094/PD-66-852.

Hemlock dwarf mistletoe (Arceuthobium tsugense) was found on mountain hemlock (Tsuga mertensiana) near Homeshore, AK. This is the first and only confirmed occurrence on this host in Alaska since a single, uncertain collection in 1913. A. tsugense infects this host less commonly in Alaska than in the western contiguous United States, where T. mertensiana is a principal host for A. tsugense. The relative infrequency of infection, unusually large swellings at the point of infection, and sparse shoot development suggest some degree of host-parasite incompatibility.