Management of Western Dwarf Mistletoe in Ponderosa and Jeffrey Pines in Forest Recreation Areas

ROBERT E SCHARPF is project leader, forest disease research, with headquarters in Berkeley, Calif. He earned a bachelor's degree in forestry (1953) at the University of Missouri, and a master's degree in forestry (1957) and a doctorate in plant pathology (1963) at the University of California, Berkeley. He joined the Forest Service in 1960 and has been with the Station's staff since then. He earned a bachelor's degree (1958) in forest management from Utah State University, and a Ph.D. in plant pathology from the University of California, Berkeley (1963). He joined the Forest Service in 1961. DETLEV VOGLER is a graduate student in plant pathology, University of California. He recently was a plant pathologist, with headquarters in San Francisco. He earned bachelor's (1965) and master's (1972) degrees from San Francisco State University, and a master's degree (1979) in plant pathology from the University of California, Berkeley. He joined the Forest Service in 1973. California is reputed to have the world's largest known "witches broom" caused by western dwarf mistletoe. The broomed tree, about 250 years old, is a major attraction on a self-guided nature trail. Western dwarf mistletoe (Arceuthobium campylopodum Engelm.) is a damaging parasite of pines in the Western United States. In high value campgrounds and recreational areas, dwarf mistletoe can be particularly damaging. Lowered life expectancy, increased hazard from defect, poor growth, and diminished esthetic or scenic values are some of the losses these parasitic plants cause in trees and forests. Resource managers now realize that many such losses in western forests are caused not by single pests alone, but by the interaction of two or more pests including insects, diseases, and animals responding to specific environmental conditions. For example, insects and diseases together killed millions of trees in California weakened by a severe drought in 1976-77. Dwarf mistletoes were among the major pests associated with this drought-related mortality. In addition, managers are increasingly aware that a single approach to control a given pest or pests is not always the best method of pest management. For instance, early attempts to eradicate dwarf mistletoes by pruning and thinning trees and stands have, for the most part, proven to be unsuccessful. The concept of "living with" dwarf mistletoe and keeping its population in check has become a more realistic approach to dealing with this disease problem. Also, the use of more than one method of managing pest complexes (more commonly …