The 2016 citizen scientist-based sudden oak death surveys (SOD Blitzes) in California forests and parks documented a substantial increase in SOD from 2015 levels associated with high rainfall levels experienced in 2016. The 2016 Blitzes detected Phytophthora ramorum (invasive, water-loving plant pathogen known to cause SOD) on multiple trees in San Luis Obispo County. Because these are the first detections of the pathogen south of Monterey County, and because SOD Blitzes findings have no regulatory implications, the UC Berkeley Garbelotto lab will be working closely with the California Department of Food and Agriculture and USDA Animal and Plant Health Inspection Service to validate the data for regulatory use.
P. ramorum was also found for the first time on Mount Diablo in Contra Costa County. Both the San Luis Obispo and Mt Diablo infestations were identified on California bay laurel. Mortality of susceptible true oaks** is not yet evident in either region, suggesting these outbreaks are recent.
The Blitzes also identified new outbreaks near Ukiah and southern coastal Mendocino County as well as in the city of Piedmont (Alameda County) and several areas east of Highway 280 on the San Francisco Peninsula. Infected trees were also detected in areas where SOD infection had subsided as a result of the drought, including northern and central Sonoma County and the Napa Valley region. A significant outbreak on bay laurels was identified in San Francisco’s Golden Gate Park near the AIDS Memorial Grove (first found positive in 2004) and, for the first time, P. ramorum was found in the San Francisco Botanical Garden at Strybing Arboretum, which houses an international plant collection. Infected trees at the Arboretum include two possible new host species; as newly identified putative hosts, their susceptibility to P. ramorum nee