Drought is decreasing but not defeating the pathogen that causes sudden oak death, according to a citizen science-assisted survey conducted this spring by a UC Agriculture and Natural Resources forest pathologist.

Results of the 2015 Sudden Oak Death Blitz survey reveal coastal mountain infestations in areas such as Big Sur (19 percent infection), the Santa Cruz Mountains (13 percent infection), and western Sonoma County (12 percent infection) remain high despite an overall decline in infection rates from 4.4 percent to 3.7 percent across California’s 15 infested counties.

Sudden oak death (SOD) symptoms have been seen in Alameda, Contra Costa, Humboldt, Lake, Marin, Mendocino, Monterey, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano, Sonoma and Trinity counties.

“Understanding the current disease distribution is key to preventing sudden oak death spread. Citizen scientists have been an invaluable help with this task over the last decade,” said Matteo Garbelotto, UC ANR Cooperative Extension specialist in the Department of Environmental Science, Policy and Management at UC Berkeley, who organizes the annual SOD Blitz.

Several new SOD outbreaks of note were identified during the blitzes. Two infected California bay laurel trees were confirmed near UC Berkeley’s West Gate, a high-traffic, high-risk area with many heritage oaks. An infected California lilac shrub was found in the Presidio of San Francisco’s (part of the Golden Gate National Recreation Area) southeastern quadrant. An infected California bay laurel tree was confirmed in Danville (eastern Contra Costa County) in an area where SOD had not previously been reported, and an urban park in Saratoga was found infested for the first time.

Read the full blog post by University of California Division of Agriculture and Natural Resources here.

Read more from Turf about sudden oak death:

Sudden Oak Death on the Rise

Foreign Invaders Target Our Trees