California Oak Mortality Task Force

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PDF ) Management Research Related Research Education and Outreach Calendar of Events The northern Humboldt County Redwood Creek watershed P. ramorum infestation appears to be restricted to one discrete location, according to collaborators who have implemented intensive surveying efforts over the past several months. Surveying efforts have taken place since the end of June, when the pathogen's presence was confirmed in water samples taken near the mouth of Redwood Creek at Orick. They have consisted of (1) numerous rhododendron leaf baits placed in the 67-mile-long river (~200,000 acre watershed) and several of its tributaries from locations high in the watershed all the way downstream; (2) two aerial survey flights conducted by the USDA Forest Service, State and Private Forestry, Forest Health Monitoring, in July and September; and (3) ground surveys of vegetation along nearly the entire lower 40 miles of river. The net result of these surveys is that the pathogen has only been found in one location centered near the community of Redwood Valley. This continues the pattern of P. ramorum generally being found near residences. The pathogen has been detected on symptomatic tanoak, California bay laurel, huckleberry, and Douglas-fir. Its effects on the latter three appear to be negligible. However, it is killing tanoaks in all size classes, including very large ones that are undetectable from the air because of the density of the Douglas-fir and redwood canopy in that location. Genetic work conducted by the UC Berkeley Garbelotto Lab on the P. ramorum isolate taken from Redwood Creek near Orick confirmed that the pathogen is of the North American (NA1) lineage. Treatment has begun on one forested property containing the majority of the infected trees. Treatments include a 300-foot treatment buffer around infected trees. Discussions are under way with neighbors who own other infested parcels to present them with similar treatment options. Efforts are under way to secure funds to support these control projects. This situation remains a very high priority for California Sudden Oak Death management, given its still-small size and remoteness from the nearest infested forests in southern Humboldt County, along with its proximity to uninfested Del Norte County, Redwood National Park, the Hoopa and Yurok Reservations, and highly productive timberlands of the north coast. For more information, contact Yana Valachovic at yvala@ucdavis.eu . P. ramorum-infested Japanese larch (Larix kaempferi) has been confirmed at 68 southwest England plantations (see http://www.forestry.gov.uk/website/forestry.nsf/byunique/infd-86ajqa ). Larch plantations with similar symptoms were also discovered in south Wales where P. ramorum was also isolated at multiple sites. Overall an estimated 600,000 mature larch over 2400 ha have been affected to date in the United Kingdom. A large area of juvenile larch is also affected. This is the first widespread and lethal damage caused by P. ramorum to a conifer and the first to a commercial plantation tree.

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