Dwarf Mistletoes Affecting Pines and Firs of Wyoming

Document Type


Journal/Book Title/Conference

University of Wyoming, Cooperative Extension Service, B-1083

Publication Date


Last Page

4 pp.


Dwarf mistletoes are parasitic flowering plants in the genus Arceuthobium. They occur widely on conifers, especially lodgepole pine, Douglas-fir, and ponderosa pine. Trees infected by dwarf mistletoe are unattractive and serve as sources of inoculum that threaten nearby healthy trees. This parasite robs trees of essential water and nutrients. Although an infected tree may survive 20 years or longer, dwarf mistletoe reduces the tree’s height and diameter. Infected trees also produce fewer viable seeds and gradually weaken from the crown or top downward and eventually die. Witches’ brooms, the large masses of twigs that sometimes form after infection, cause lumber defects by forming large knots. Witches’ brooms also are hazardous because they may break off the tree and fall, possibly damaging property or injuring people and pets.