Bruce McConnell plucked a leaf from a scruffy little bay tree on a steep, rocky Fountaingrove hillside overlooking the Santa Rosa Plain.
“Here's your clue,” he said, pointing to a brownish stain at the edge of the leaf, a telltale sign of the as yet unstoppable disease that is ravaging Sonoma County's woodlands.
Sudden oak death, discovered in Marin County in 1995, has now killed about 257,000 tanoak and oak trees in 14 counties from Monterey to Humboldt, leaving property owners grasping for ways to at least slow the pathogen's onslaught.
“These trees need our help,” said McConnell, who can see the bay tree from his home on Shillingford Drive in the Fountaingrove II subdivision.
Nearly 600 homeowners in the upscale development are spending $8,000 a year to spray the trunks of 400 large oaks surrounding their homes with a chemical considered the best defense, but by no means a cure, for the disease.
At least five oaks in Fountaingrove's 200 acres of open space are infected by the pathogen that rides wet spring winds from unharmed host bay trees to four types of oak trees, including coast live oak and black oak common to Sonoma County, as well as tanoaks, which are not a true oak.
“Once your trees become infected, there is no hope — and the danger of the trees or their limbs suddenly crashing onto your home or loved ones becomes a frightening reality,” warns the Fountaingrove II Open Space Maintenance Association's website.
A dry spring curbed the rate of infection documented by the sixth annual Sudden Oak Death Blitz organized by UC Berkeley's Forest Pathology Laboratory.
More than 400 volunteers in 16 greater Bay Area communities collected leaves from 2,020 trees, enabling Matteo Garbelotto's lab to calculate an overall 7.38 percent rate of infection.
In Sonoma County, McConnell was one of 46 volunteers who sampled 193 trees, which were determined to have a 5.57 percent infection rate, eighth-lowest among the communities ranging from Mendocino County to San Francisco and the East Bay, and from the Peninsula down to San Luis Obispo.