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Effects of Comandra Blister Rust and Dwarf Mistletoe on Cone and Seed Production of Lodgepole Pine. Bruce Schaffer, Graduate Research Assistant, Department of Forest and Wood Sciences, Colorado State University, Fort Collins 80523. F. G. Hawksworth, Research Plant Pathologist, USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins 80523; and W. R. Jacobi, Assistant Professor, Department of Botany and Plant Pathology, Colorado State University, Fort Collins 80523. Plant Dis. 67:215-217. Accepted for publication 14 July 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, 1983. DOI: 10.1094/PD-67-215.

Effects of comandra blister rust (Cronartium comandrae) and dwarf mistletoe (Arceuthobium americanum) on cone and seed production of infected lodgepole pine trees were determined. Trees infected with C. comandrae in the Shoshone National Forest, WY, were given comandra rust ratings based on Brown's 8-class system. Trees infected with A. americanum in the Roosevelt National Forest, CO, were given dwarf mistletoe ratings based on Hawksworth's 6-class system. Cone and seed numbers, cone and seed sizes, the percentage of filled seed, and the percentage of viable seed were compared with the disease severity for each of the diseases. Reduction of live crown size in trees heavily infected with C. comandrae resulted in significantly fewer cones and seeds than were found in healthy trees. Trees heavily infected with dwarf mistletoe had significantly smaller cones and seeds, which may have been a result of a reduction in tree vigor caused by the parasite.