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Foliage infected with P. gaeumannii may range in colour from (normal) dark green to pale green to yellowish-brown. The pattern of discoloration within a needle may be uniform or mottled, frequently beginning at the needle tips, and is more severe in the older foliage. Premature needle abscission begins with the older, more severely infected foliage. At its most severe, complete abscission of all but the current-year needles may be observed.
P. gaeumannii is effectively controlled by protectant fungicides applied to emergent foliage during the infection period. The fungicide chlorothalonil has been effective in controlling Swiss needle cast in Christmas tree plantations. Two spray applications are recommended, the first shortly after bud burst and the second 3-4 weeks later (Chastagner and Byther, 1983). Limited control of Swiss needle cast in forest plantations in New Zealand was achieved using copper fungicides (Hood and van der Pas, 1979). However, use of chemical fungicides for control of Swiss needle cast in forest plantations is not considered economically viable in addition to environmental health considerations. No biological control methods are known. Disease can also be controlled by judicious selection of appropriate planting stock.
The worldwide impact of P. gaeumannii has not been determined. In Oregon, USA, Swiss needle cast disease is a serious forest health problem currently affecting some 109,000 ha of forest land in the west of the state encompassing private, state, federal and tribal land ownerships. Volume growth losses as a result of Swiss needle cast in the affected area are estimated at between 23 and 52% depending on disease severity (Maguire et al., 2002). For 76,000 ha of Douglas-fir plantations aged 10-30 years between Newport and Astoria, Oregon, volume losses of 43 million board ft per year with a value of $21.5 million per year were estimated (D Maguire, Oregon State University, Department of Forest Science, personal communication, 2004). Extrapolating the entire area affected by Swiss needle cast, annual growth losses to the disease are conservatively valued at over $30 million per year. Swiss needle cast also affects the Douglas-fir Christmas tree industry, valued at about $100 million per year, in Oregon and Washington. The economic effects of Swiss needle cast to the Christmas tree industry include costs of protective fungicide sprays as well as losses due to disease. It is estimated that 4000-8000 ha of Christmas trees are sprayed annually for control of Swiss needle cast (GA Chastagner, Washington State University, Department Plant Pathology, personal communication, 2004).