First Report of Lodgepole Pine Dwarf Mistletoe on Subalpine Fir. R. L. Mathiasen, Idaho Department of Lands, P.O. Box 670, Coeur d'Alene 83816. J. S. Beatty, USDA Forest Service, Forest Insects and Diseases, Columbia River Ranger Station, 31520 SE Woodard Road, Trout-dale, OR 97060; and D. M. Hildebrand, USDA Forest Service, Forest Insects and Diseases, P.O. Box 3623, Portland, OR 97208. Plant Dis. 80:342. Accepted for publication 4 January 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0342A.
Lodgepole pine dwarf mistletoe (Arceulhobium americanum Nutt. ex Engelm.) was observed parasitizing subalpine fir (Abies lasiocarpa (Hook.) Nutt. var. lasiocarpa) that were growing near heavily infected lodgepole pine (Pinus contorta Douglas & Loud var. latifolia (Engelm. ex S. Wats.) in mixed conifer forests on the southeast slopes of Mount Adams approximately 15 km north of Trout Lake, WA. Although many subalpine fir were observed growing in close proximity to heavily infected lodgepole pine, only a few infected subalpine fir were observed. Affected subalpine fir were typically heavily infected. Infected branches were usually distinctly swollen, formed dense witches'-brooms, and produced few or no mistletoe shoots. Mistletoe shoots on subalpine fir were morphologically similar to A. americanum shoots produced on nearby infected lodgepole pine. Subalpine fir is best classified as a rare host of A. americanum based on the host susceptibility classification developed by Hawksworth and Wiens (USDA Agric. Handb. 401, 1972). Specimens of A. americanum on subalpine fir were collected (Yakima County, T.07N., R.11E., Sec. 8, NW 1/4, 1,400 m) and have been deposited at the USDA Forest Service Forest Pathology Herbarium in Fort Collins, CO. This is the first report of A americanum parasitizing subalpine fir.