United States Department of Agriculture Mistletoes of North Forest Service Rocky Mountain Research Station American Conifers General Technical Report RMRS-GTR-98 September 2002 Canadian Forest Service Department of Natural Resources Canada Sanidad Forestal SEMARNAT Mexico Abstract _________________________________________________________ Geils, Brian W.; Cibrián Tovar, Jose; Moody, Benjamin, tech. coords. 2002. Mistletoes of North American Conifers. Gen. Tech. Rep. RMRS–GTR–98. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 123 p. Mistletoes of the families Loranthaceae and Viscaceae are the most important vascular plant parasites of conifers in Canada, the United States, and Mexico. Species of the genera Psittacanthus, Phoradendron, and Arceuthobium cause the greatest economic and ecological impacts. These shrubby, aerial parasites produce either showy or cryptic flowers; they are dispersed by birds or explosive fruits. Mistletoes are obligate parasites, dependent on their host for water, nutrients, and some or most of their carbohydrates. Pathogenic effects on the host include deformation of the infected stem, growth loss, increased susceptibility to other disease agents or insects, and reduced longevity. The presence of mistletoe plants, and the brooms and tree mortality caused by them, have significant ecological and economic effects in heavily infested forest stands and recreation areas. These effects may be either beneficial or detrimental depending on management objectives. Assessment concepts and procedures are available. Biological, chemical, and cultural control methods exist and are being developed to better manage mistletoe populations for resource protection and production. Keywords: leafy mistletoe, true mistletoe, dwarf mistletoe, forest pathology, life history, silviculture, forest management Technical Coordinators_______________________________ Brian W. Geils is a Research Plant Pathologist with the Rocky Mountain Research Station in Flagstaff, AZ. Dr. Geils earned a Master of Science degree in forestry at the University of Idaho and a Ph.D. degree in plant pathology at Colorado State University. His current research focuses on the epidemiology and ecological effects of rusts and dwarf mistletoes in the interior western United States. Jose Cibrián Tovar is Director of Sanidad Forestal, SEMARNAT, Mexico D.F. He has investigated the distribution and effects of dwarf mistletoes in Mexico and now leads the forest health program for Mexico. Benjamin Moody is Science Advisor on pest management for the Canadian Forest Service, Department of Natural Resources Canada, Ottawa, Ontario. Dr. Moody obtained a Master of Science degree in forestry from the University of New Brunswick and a Ph.D. degree in forestry from the University of British Columbia. He serves as national advisor for the forest insect and disease research programs and provides guidance on forest insect and disease issues for federal policy and management development. You may order additional copies of this publication by sending your mailing information in label form through one of the following media. Please specify the publication title and number. Telephone (970) 498-1392 FAX (970) 498-1396 E-mail [email protected] Web site http://www.fs.fed.us/rm Mailing Address Publications Distribution Rocky Mountain Research Station 240 West Prospect Road Fort Collins, CO 80526 Mistletoes of North American Conifers Technical Coordinators: Brian W. Geils Jose Cibrián Tovar Benjamin Moody Sponsors: Forest Service, U.S. Department of Agriculture, U.S.A. Sanidad Forestal, SEMARNAT, Mexico Canadian Forest Service, Department of Natural Resources Canada Preface _______________________ cies names or combinations are proposed. The nomen- clature used in this book for mistletoes is adapted from The mistletoes are serious disease agents affecting several sources including taxonomic publications by forests in all three countries represented by the North Hawksworth, Wiens, and others (see Hawksworth and American Forestry Commission (NAFC 2002): Canada, Wiens 1996), the International Plant Names Index (Plant Mexico, and the United States of America. For this Names Project 1999), the VAST database (Missouri reason, the Commission through its Insect and Disease Botanical Garden 2002), and the National PLANTS data- Study Group has asked us to prepare a practical guide for base (USDA, NRCS 2001). field foresters. This publication provides basic informa- The taxonomy of many host groups is also subject to tion on the species of mistletoes, their hosts, distribu- uncertainty, disagreement, and revision. The names of tions, effects, methods of evaluation, and management. many hosts cited in the literature are no longer accepted, This work updates and expands the several pages dedi- and the proper name for a population in question may not cated to mistletoes in the previous guide produced for the be apparent. The host taxonomy accepted here follows NACF (Davidson and Prentice 1967). This book covers the Flora of North America (Flora of North America the mistletoes (Loranthaceae and Viscaceae) that para- Committee 1993) for Canada and the United States and sitize conifer hosts and occur in North America (Canada, Perry (1991) for Mexico. These sources also provide United States, and Mexico). A similar management syn- valuable host information including description, synonymy, opsis but from a different perspective is available for the and distribution. Nomenclatures for taxa not represented mistletoes of eucalypts in Australia (Reid and Yan 2000). in these sources (and some authorities) are from the The literature on mistletoes is large (over 5,700 articles International Plant Names Index (Plant Names Project on North American mistletoes) but widely scattered for 1999). some topics and rare for other topics. We intend this Because this book has international readership in synoptic review as a guide to useful references for several languages (English and Spanish), we usually addressing management concerns from biological con- refer to plants by their scientific name. To accommodate servation to wood fiber production. Because many refer- those not familiar with these names, we provide appendix ences have been already cited by Hawksworth and B, relating scientific and vernacular names for trees Wiens (1996) for the dwarf mistletoes, we give emphasis species; and we refer to common genera in the text as to general reviews, recent publications, and information “pines” for Pinus and “dwarf mistletoes” for Arceuthobium. on other mistletoes. An extensive, searchable, anno- The formal nomenclature for mistletoes including author- tated bibliography (and other information) is available at ity, publication, and common synonyms is given for each the Mistletoe Center (2002). To facilitate use of this mistletoe before its description. guide, we provide a glossary for specialized terms (see The technical editors are grateful to the many sup- appendix D) and post the text online. porters, contributors, reviewers, and editors who helped Many chapters in this book were first drafted by F. G. to prepare and publish this guide (see appendix C). We Hawksworth and D. Wiens as they were preparing bo- thank C. G. Shaw and Jerome Beatty, USDA Forest tanical monographs for Phoradendron and for Service, Washington Office, for their helpful support to Arceuthobium (published as Hawksworth and Wiens this project. We also thank the members of the NAFC, 1996). Although information in this book has been se- Insect and Disease Study Group for encouraging and lected, revised, and updated, the present authors and supporting this work. The NAFC (2002) is a commission technical editors acknowledge Hawksworth and Wiens of the Food and Agriculture Organization of the United as the original source for many passages of text. Nations and consists of the national forest agencies of The systematics of Psittacanthus, Phoradendron, and Canada, the United States, and Mexico. Specialists Arceuthobium are the active subjects of current re- from the represented countries meet in study groups to search; taxonomic revisions of these genera are ex- exchange technical assistance on insects and dis- pected in the near future. This book is not a systematics eases, tree improvement, silviculture, fire management, and taxonomic review of these mistletoes; no new spe- and other topics. Technical Coordinators Brian W. Geils Jose Cibrián Tovar Benjamin Moody September 2002 Author Profiles ________________________________ Frank G. Hawksworth died in 1993 after starting this project and a monographic review of the genus Arceuthobium. He had been Project Leader and Supervisory Plant Pathologist with the Rocky Mountain Research Station in Fort Collins, CO. Beginning with his doctoral studies at Yale University, Dr. Hawksworth dedicated his professional life to the single question, “What is mistletoe?” He described numerous species (most with Del Wiens), authored over 275 articles on dwarf mistletoes, and compiled an extensive library on mistletoes of the world. He is commemorated by Arceuthobium hawksworthii. Delbert Wiens is retired Professor of biology, University of Utah, Salt Lake City. He received a Ph.D. degree from the Claremont Graduate School, CA for his work on the taxonomy of Phoradendron. Dr. Wiens has investigated numerous aspects of plant biology including systematics, biogeography, cytology, reproductive biology, and mimicry. He has a particular interest in the Loranthaceae and Viscaceae