Ecology of Swiss needle cast in Western Oregon Coastal forests: ecophysiology and tree ring analysis correlate intensification to climate warming.
D. C. SHAW (1). (1) Dept. of Forest Engineering, Resources, and Management, Oregon State University, Corvallis, OR, U.S.A.
<i>Phaeocryptopus gaeumannii</i>, cause of Swiss needle cast of Douglas-fir (<i>Pseudotsuga menziesii), </i>has intensified in western Oregon and Washington, USA since 1980’s. Manter and colleagues demonstrated <i>P. gaeumannii</i>, an endophytic biotroph, caused disease by carbon starvation due to ascocarps (pseudothecia) plugging the stomates. ~25% stomatal occlusion was associated with no net carbon gain for a leaf. Manter et al. used field, laboratory, and greenhouse studies to build an epidemiology model that included Dec, Jan, Feb mean daily temperature and a leaf wetness factor for May, June and July (the period of potential spore dispersal). Saffell et al. used fungicide treated and un-treated trees to demonstrate carbon stable isotope discrimination (Δ<sup>13</sup>C) of treated Douglas-fir was greater than untreated and used tree ring analysis to predict precipitation in the previous 2 summers most influenced disease. Black and colleagues demonstrated that dendrochronology could be used to find a tree-ring-reduced-growth signal and indicated that deviation in growth from a companion species (<i>Tsuga heterophylla</i>) has occurred since the 1980’s. Black et al. developed a climate-based disease severity model using data from 3 sites that linked March-August temperature to intensification of disease and showed a correlation with 1960-2000 weather records when consistent warming occurred during these months.
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