History of the Problem

Swiss needle cast disease of Douglas-fir is caused by the ascomycete Phaeocryptopus gaeumannii (Rohde) Petrak. The disease, and the fungus that causes it, were first described from Douglas-fir plantations in Switzerland and Germany in 1925, and soon afterward reported from various locations in Europe, the British Isles, and Northeastern North America (Boyce 1940, Peace 1962). The causal agent, P. gaeumannii, was found to be abundant on foliage of diseased trees and was determined to be distinct from any previously described foliage fungi from coniferous hosts. Subsequent surveys of Douglas-fir in the Western United States found the pathogen was widespread throughout the Pacific Northwest region, where it had escaped notice because of its inconspicuous habit and negligible effect on its host. Boyce (1940) considered P. gaeumannii widespread but harmless on Douglas-fir in Western North America, and probably indigenous to the Pacific Northwest, where “...the fungus has been found at such widely separated localities in British Columbia, Washington, and Oregon that it must be considered generally distributed, although harmless, in the Douglas-fir region of the Pacific coast.”

Symptoms of Swiss needle cast

Douglas-fir is the only host of P. gaeumannii, which has accompanied cultivation of its host to various localities worldwide (Hood 1997, Temel and others 2003). Diseased trees have chlorotic foliage and may lose all but the current year’s complement of needles (see figure at right). The earliest confirmed records of P. gaeumannii in Western North America are herbarium specimens collected by J.S. Boyce from Oregon and California in 1916 (Boyce 1940). The fungus occurs on both coastal (Pseudotsuga menziesii var. menziesii) and interior (P. menziesii var. glauca (Beissn.) Franco) forms of Douglas-fir throughout the natural range of the host (Boyce 1940, Hood 1982). The fungus has also been reported from P. macrocarpa (Vasey) Mayr in New Zealand (Gadgil 2005), although it has not been reported on this host in North America.

Although Swiss needle cast disease in Europe first brought attention to Phaeocryptopus gaeumannii, the fungus has long been considered a pathogen of negligible significance in Western North American forests. Peace (1962) wrote of Swiss needle cast disease in Europe: “This is a classic case of a disease, of no importance in its native haunts, which has become damaging when transported to other areas.” With the growth of a commercial Douglas-fir Christmas tree industry in the Pacific Northwest in the 1970s, and the practice of shearing trees to promote a more compact growth form, Swiss needle cast first began to attract serious notice in its native region (Michaels and Chastagner 1984). Although episodic outbreaks of brief duration in forest plantations in the Pacific Northwest were noted in the 1970s and 1980s (Russell 1981), Swiss needle cast was not considered a significant forest pathogen. The occurrence of Swiss needle cast disease primarily in forest plantations outside the native range of Douglas-fir, or on sheared Christmas tree plantations, has contributed to the perception of the disease as being primarily associated with inappropriate planting stock or stressed trees.