Sudden Oak Death, Tree Pathogen, Rapidly Killing Northern California Forests

Researchers at UC Berkeley recently completed a survey of the health of Northern California's forests and the results aren't pretty. A microbial disease called Sudden Oak Death is sweeping through the region at a blinding rate, increasing in prevalence nearly tenfold over last year.

The San Francisco Chronicle notes a study conducted by the U.S. Forestry Service which documented 375,700 news cases of dead oak trees spanning 54,400 acres of California this year, up from 38,000 cases over 8,000 acres a year ago.

This exponential growth in cases over last year is made even more disturbing by the previous year's study, which found a 200-300% increase in Sudden Oak Death between 2010 and 2011.

According to California Oak Mortality Task Force spokesperson Katie Palmieri, the reason behind this rapid expansion is largely due to weather--two wet years followed by a very dry one. "We've seen this pattern before after wet years," she told the Chronicle. "The key to all this is rapid response so we can see containment and hopefully eradication."

Sudden Oak Death is a disease caused by the plant pathogen Phytophthora ramorum and has a deadly effect on oak trees as well as a number of other plant species. It has been found in tree populations in California, Oregon and parts of Europe.

The U.C. Berkeley Department of Forest Pathology and Mycology undertook a Sudden Oak Death Blitz this year where individual volunteers went out on weekends and collected leaf samples for study. Researchers discovered the infection rate varied wildly between the twelve counties studied. Places like San Francisco and Los Altos had infection rates that could be as low as under one percent; however, other areas were much more deeply affected. Marin County, where Sudden Oak Death was first discovered in the mid-1990s, had an infection rate just above 50 percent and Saratoga's rate may be near 60 percent.

Last year, researchers discovered one section of forest near Skyline Boulevard between Saratoga and Los Gatos where 97 percent of the trees present carried the pathogen.

In San Francisco's Golden Gate Park, three trees near Middle Lake were also found to have Sudden Oak Death. This is the second time the disease has been detected in the park, but Parks Department officials believe the infection is still in an early stage and can hopefully be contained.

Other plants, such as rhododendron and bay laurels, can serve as hosts for the disease. The San Jose Mercury News reports that researchers have urged Northern California homeowners to check for leaf blot on their plants, which is a symptom of the disease, to stop it from spreading.

Despite the increased prevalence of Sudden Oak Death, a recent breakthrough by scientists at Marin County's Dominican University has found a simple, effective way to combat the disease. The Marin Independent Journal reports:

On Tuesday, scientists at the three-year-old National Ornamental Research Site at Dominican University in San Rafael unveiled breakthrough "green" technology they have developed using an ordinary commercial steamer to heat soil to 122 degrees, killing the sudden oak death pathogen.

"It's low-tech and high impact," said principal investigator Sibdas Ghosh, chairman of Dominican's Department of Natural Sciences and Mathematics.

A free, open-to-the-public town hall on the spread of Sudden Oak Death is scheduled for Friday, November 9th at 7 p.m. at 1710 Socol Ave. in Napa.