Sudden oak death spreading in the Bay Area

The Forest Pathology and Mycology Laboratory at UC Berkeley used 10,000 tree and plant samples collected by 500 citizens between April and June this year to document a dramatic increase in the infection rate of sudden oak death (SOD) from Napa to the Carmel Valley and virtually everywhere in between.

"We found that the number of positives were double and in some cases triple what they were last year," said Matteo Garbelotto, the UC Berkeley forest pathologist who organizes the annual surveys. "We were surprised. That was a big jump."

The findings are part of a major effort over the past four years to involve citizens in the battle against the mysterious pathogen, which has killed hundreds of thousands of oak trees from Big Sur to southern Oregon.

Arborists and ecologists are afraid that sudden oak death could eventually denude California's golden hills of its signature tree. As it is, experts predict as many as 90 percent of California's live oaks and black oaks could die from the disease within 25 years.

The citizen scientists, who were trained to detect disease symptoms, surveyed about 50,000 acres and collected samples from 2,000 oak and bay trees during a series of so-called SOD blitzes.

The information was added to a Bay Area-wide map plotting the tree-strangling microbe's path of destruction. New infestations were found this year in and around neighborhoods throughout the region, including urban and suburban areas of Napa, Berkeley and other locations in southern Alameda County.

The largest infestation was along South Skyline Boulevard, west of Saratoga and Los Gatos, where 97 percent of the specimens that were collected tested positive for the pathogen.

Garbelotto, who is one of the nation's foremost experts on sudden oak death, said the positive tests in this woodsy region were not a surprise. The area is a known hot spot for the disease. This was, nevertheless, the first comprehensive survey done in the area, he said, and it came out worse than expected.

"We confirmed that it's at epidemic levels," he said, "but we didn't expect to find 97 percent."

The infection rate was also disturbingly high around Woodside, in the Portola Valley, with 70 percent of the samples testing positive. A year ago, 24 percent of the samples tested positive in that area.

Marin County has also been ravaged by the disease, with 53 percent of the samples there testing positive compared with 35 percent a year ago. Menlo Park, Atherton, the Los Altos Hills, the Carmel Valley, Sonoma and Napa counties also had numerous positive tests.

The most surprising result, Garbelotto said, was the fact that the disease had moved into residential areas, including North Berkeley, the Claremont district in Berkeley and the Montclair area of Oakland. Positive tests were recorded in East Richmond, San Leandro and at the Oakland Zoo.

Infected trees were even found in the Sunol area of eastern Alameda County, which was thought to be too dry for the disease.

"I didn't expect it to be that widespread," Garbelotto said. "It looks like it's coming down the slopes toward the bay. Pretty much from San Leandro to Richmond, we are seeing the disease move westward."

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