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    Author(s): Tedmund J. Swiecki; Elizabeth Bernhardt
    Date: 2015
    Source: Gen. Tech. Rep. PSW-GTR-251. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 563-572
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: Download Publication  (346.0 KB)


    From 2000 through 2012, we collected annual observations on disease symptoms and stand conditions in 128 coast live oak plots in forests affected by sudden oak death (SOD), caused by the introduced pathogen Phytophthora ramorum. Elevated rainfall in one or both of the previous wet seasons was associated with pulses of new infections. However, persistent differences in infection rates between nearby locations and among plots within locations show that tree and site specific factors influence disease risk on the local scale. Because California bay is the primary source of P. ramorum spores in these affected forests, variables describing the proximity and density of California bay in the local oak neighborhood are the strongest predictors of disease risk. Tree growth rate and bark characteristics are also predictors of disease risk. Faster-growing, more dominant trees had elevated SOD risk whereas trees declining from other diseases had reduced SOD risk. Coast live oaks with SOD followed one of several disease progress trajectories, ranging from rapid decline to disease remission. Extensive initial trunk girdling by cankers was associated with rapid decline. More than half of the trees that developed symptoms between 2001 and 2010 had inactive or undetectable cankers by 2012.

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    Swiecki, Tedmund J.; Bernhardt, Elizabeth. 2015. Phytophthora ramorum canker (Sudden Oak Death) disease risk and progress in coast live oak, 2000-2012. In: Standiford, Richard B.; Purcell, Kathryn L., tech. cords. Proceedings of the seventh California oak symposium: managing oak woodlands in a dynamic world. Gen. Tech. Rep. PSW-GTR-251. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 563-572.


    California bay, disease remission, Quercus agrifolia, resistance, risk model, susceptibility, symptoms, Umbellularia californica

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