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Title: A CLIMATE BASED MODEL FOR PREDICTING GEOGRAPHIC VARIATION IN SWISS NEEDLE CAST SEVERITY IN THE OREGON COASTAL RANGE

Author
item Manter, Daniel
item REESE, PAUL - OSU, CORVALLIS, OR
item STONE, JEFFREY - OSU, CORVALLIS, OR

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2005
Publication Date: 7/12/2005
Citation: Manter, D.K., Reese, P.W., Stone, J. 2005. A climate based model for predicting geographic variation in Swiss needle cast severity in the Oregon coastal range. Phytopathology. 95:1256-1265.

Interpretive Summary: Since the early 1990s Swiss needle cast disease has been increasing in Douglas-fir plantations in the Oregon Coast Range. Considerable variation in disease severity across the affected area often has been noted. We investigated the influence of site microclimate on fungal colonization as a basis for this variation with a combination of seedling inoculation and field studies. Development of P. gaeumannii ascocarps on inoculated seedlings subjected to mist, irrigation, and shading treatments was followed for 10 months. Contrary to expectations, numbers of ascocarps on foliage were negatively correlated with wetness and positively correlated with temperature. Numbers of ascocarps on foliage, site temperature and leaf wetness were monitored over four years at nine field sites in the Oregon Coast Range. Factors most highly correlated with ascocarp abundance were winter mean daily temperature and spring cumulative leaf wetness. Predictive models for disease severity based on these correlations were tested against disease and climate data measured at field sites during 2003-2004. A temperature-based disease prediction model was developed in combination with GIS-linked climate databases to estimate disease levels across a portion of the Oregon Coast Range. This model can be used for hypothesis testing and as a decision support tool for forest managers.

Technical Abstract: Since the early 1990s Swiss needle cast disease has been increasing in Douglas-fir plantations in the Oregon Coast Range. Considerable variation in disease severity across the affected area often has been noted. We investigated the influence of site microclimate on fungal colonization as a basis for this variation with a combination of seedling inoculation and field studies. Development of P. gaeumannii ascocarps on inoculated seedlings subjected to mist, irrigation, and shading treatments was followed for 10 months. Contrary to expectations, numbers of ascocarps on foliage were negatively correlated with wetness and positively correlated with temperature. Numbers of ascocarps on foliage, site temperature and leaf wetness were monitored over four years at nine field sites in the Oregon Coast Range. Factors most highly correlated with ascocarp abundance were winter mean daily temperature and spring cumulative leaf wetness. Predictive models for disease severity based on these correlations were tested against disease and climate data measured at field sites during 2003-2004. A temperature-based disease prediction model was developed in combination with GIS-linked climate databases to estimate disease levels across a portion of the Oregon Coast Range. This model can be used for hypothesis testing and as a decision support tool for forest managers.