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Abstract
One hundred-thirteen sites were established in perennial watercourses and sampled for 1 to 3 years between 2004 and 2006 to monitor for presence of
Phytophthora ramorum throughout coastal central and northern California watersheds as well as portions of the Sierra Nevada mountain range (Murphy and others 2006). The majority of the monitored watersheds have limited or no
P. ramorum at this time, but are near the epidemic range of
P. ramorum and/or are considered high-risk for invasion by
P. ramorum. Three currently infested watersheds in Sonoma and Mendocino counties were included as a baseline for successful recovery of
P. ramorum. Rhododendron leaves were placed in fiberglass mesh bags, secured to streambanks, and floated on the water surface for 1 to 3 week intervals to bait for
Phytophthora species (von Broembsen 2002; E. Hansen, personal communication 2003; P. Maloney and J. Davidson, personal communication 2003). The interval time was adjusted year round with the minimum time during periods of warm stream and air temperatures and longer intervals in cold conditions. Recovered symptomatic leaves were described and isolated onto
Phytophthora-selective medium augmented with 25 mg/L hymexazol to inhibit growth of
Pythium species (PARP-H). Experiments have shown minimal inhibition of
P. ramorum and other
Phytophthora species growth with this concentration of hymexazol (Fichtner and others 2006; Murphy, unpublished data; E. Hansen, personal communication 2004; S. Jeffers, personal communication 2005). Plates were incubated at 18°C for three weeks and checked microscopically twice weekly for growth of
Phytophthora species; any
Phytophthora-like organisms were transferred and further examined for identification.
Parent Publication
Citation
Murphy, S.K.; Lee, C.; Valachovic, Y.; Bienapfl, J.; Mark, W.; Jirka, A.; Owen, D.R.; Smith, T.F.; Rizzo, D.M. 2008. Monitoring
Phytophthora ramorum distribution in streams within California watersheds. In: Gen. Tech. Rep. PSW-GTR-214, Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture. pp 409-411
