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Washington State University
WSU Puyallup Ornamental Plant Pathology

Sudden Oak Death Is Still Spreading, Still A Threat

By Michael Joyce, Jefferson Public Radio

Reports on Sudden Oak Death don’t seem to be nearly as common as they were a few years ago. The invasive plant disease, which has devastated oak stands along the West Coast, continues to spread in northwestern California and southwestern Oregon. But funding, public engagement, and solutions have been hard to come by.

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Native plant nurseries

Fourteen native plant nurseries have joined the California Department of Food and Agriculture (CDFA) Best Management Program (BMP) for Ornamental and Native Plant Nurseries. The program also serves 14 ornamental nurseries. The discovery of Phytophthora tentaculata infecting several native plant species in nurseries and restoration sites has alerted the industry to the cryptic nature of plant pathogens and how easily they can move into the environment. Although the program has been voluntary to date, with the nurseries choosing which BMPs to employ, CDFA and the National Ornamentals Research Site at Dominican University of California are working to identify minimum requirements for acceptance into the program for ornamental interstate shipping nurseries as well as native plant nurseries. CDFA is developing a website to further support the BMP Program.

For more information on this and other news items, read the COMTF monthly newsletter.

Native plant nurseries in Washington interested in participating in a multistate research program in 2015-2016 are encouraged to contact Marianne Elliott ( for information. The program will investigate the movement of Phytophthora species among nurseries, restoration sites, and forests.

Update on Kitsap Co. garden site

The Kitsap County botanical garden found to have a P. ramorum-positive Pieris plant in April had additional positive plants found in May during the delimitation survey. All infected plants were destroyed and trace-back investigations are underway. The facility will undergo a Critical Control Point Assessment (CCPA) at which time best management practice (BMP) mitigations will be identified for implementation. The BMPs will be enforced through a state compliance agreement. Federal regulatory oversight will continue to ensure the pathogen is being managed effectively.

For more information on this and other news items, read the COMTF monthly newsletter.

New Pr hosts found

Five new Phytophthora ramorum hosts were detected during a rare plant survey in February on Marin County Municipal Water District property when unusual Arctostaphylos symptoms were identified. Samples submitted to the California Department of Food and Agriculture (CDFA) Plant Pest Diagnostics Lab tested negative for root pathogens, but the leaves and branches tested positive for P. ramorum. Follow-up official samples were collected for testing by CDFA scientists, which resulted in the identification of five new P. ramorum hosts: Arctostaphylos virgata, Arctostaphylos glandulosa, chinquapin (Chrysolepsis chrysophylla), blackberry (Rubus ursinus), and chaparral pea (Pickeringia montana). Arctostaphylos virgata and Arctostaphylos glandulosa symptoms include leaf spots and necrosis, petiole dieback, stem lesions and cankers, and tip dieback. Many plants of both species were showing symptoms. Chinquapin (Chrysolepsis chrysophylla) symptoms include canopy dieback, leaf spots, and vascular discoloration. Many chinquapin were showing symptoms; two trees were confirmed positive. Blackberry (Rubus ursinus) symptoms include leaf spots and stem lesions. Chaparral pea (Pickeringia montana) symptoms include leaf spots, stem lesions, and thorn dieback. CDFA scientists are in the process of obtaining healthy container plants of each host species to confirm pathogenicity. A follow-up site visit to the water district is planned for July to observe disease progression on these hosts.

Vaccinium parvifolium (red huckleberry) was found P. ramorum positive for the first time from two samples taken at a Lewis County, WA interstate shipping nursery during their 2015 spring Federal P. ramorum Certification Program survey. The Lewis County facility was also positive in 2014 and had undergone a CCPA as well as extensive mitigation activities. A new CCPA has been conducted to determine possible ways the pathogen has continued to infect plant material; additional mitigation efforts will completed in 2015. As a result of the new host confirmation, Vaccinium parvifolium will be added to the federally recognized P. ramorum host and associated host list.

For more information on this and other news items, read the COMTF monthly newsletter.