Dwarf mistletoes on western white pine and whitebark pine in northern California and southern Oregon

Pinus monticola is a principal host of Arceuthobium californicum in the Siskiyou Mountains, and suffers extensive mortality in some stands. Whitebark pine P. albicaulis is a principal host and western white pine is a secondary host for A. cyanocarpum in N California. Mortality of whitebark pine caused by this dwarf mistletoe on Mount Shasta, California, is as high as 58%. Western white pine is occasionally infested in A. tsugense infested mountain hemlock stands in California and S Oregon. However, no infection of western white pine occurred in A. tsugense-infested western hemolock stands in S Oregon, indicating there are physiologically distinct races of A. tsugense parasitizing western hemlock Tsuga heterophylla and mountain hemlock T. mertensiana. -from Authors