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.
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