Eradication of Phytophthora Ramorum from Oregon Tanoak Forests - Status after Three Years

Alan Kanaskie, Oregon Department of Forestry, 2600 State Street, Salem OR USA 97310; 503-945-7397; akanaskie@odf.state.or us; Nancy Osterbauer, Oregon Department of Agriculture, Salem OR USA; Michael McWilliams, Oregon Department of Forestry, Salem OR USA; Ellen Goheen, USDA Forest Service, SW Oregon Forest Insect and Disease Service Center, Central Point OR USA; Everett Hansen and Wendy Sutton, Department of Botany and Plant Pathology, Oregon State University, Corvallis OR USA.

Since July 2001 we have been attempting to eradicate Phytophthora ramorum from tanoak forests in southwestern Oregon by cutting and burning all infected host plants and adjacent apparently uninfected plants. On many sites the pathogen survived the initial treatment and was present in stump sprouts of host vegetation one year after treatment. Vegetation sprouting from stumps following the initial treatment is being destroyed mechanically or with herbicides. Eradication is in progress on approximately 36 sites, totaling 70 acres. Monitoring vegetation, soils, and stream water within the eradication sites has shown that the pathogen survived cutting and burning on more than 50 percent of the sites. The number of new infected trees discovered each year has decreased since we first discovered the pathogen in Oregon. Most new infected trees occurred within 100 meters of existing eradication sites, and a few were found up to 3 kilometers from the nearest eradication site. Repeated aerial surveys and ground-checks have failed to detect the pathogen in Oregon forests beyond this limited area. Despite several new occurrences of P. ramorum in 2003 and 2004, these results suggest that the eradication effort has reduced inoculum levels and slowed spread of the pathogen.

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