Sudden Oak Death, a disease that has plagued the oak and tanoak tree population in California for the past 20 years, has killed more trees this year than in the last two years, leading UC Berkeley researchers to be concerned that the epidemic is becoming more deadly.
The disease has been infecting oak and tanoak trees around the bays of California since its discovery in the 1990s, and this year, the number of trees killed indicates that a wave of the disease is spreading throughout the state, according to Katharine Palmieri, the spokesperson for the California Oak Mortality Task Force.
An annual aerial survey from the U.S. Department of Agriculture Forest Service found 376,000 dead oak and tanoak trees over 54,000 acres in California’s impacted areas, compared to 38,000 trees across 8,000 acres mapped in the same area in 2011.
Palmieri said the pathogen is primarily spread through the spores of infected plants but is expedited by the presence of water.
According to Matteo Garbelotto, the head of the UC Berkeley Forest Pathology and Mycology Lab, the heavy rains in 2011 are a major factor in the rapid spread of the disease this year.
Palmieri said that while there are as many as 137 different types of plants infected by the disease, oak and tanoak trees are some of the only plants killed by the disease.
“Oaks are a keystone species, which means they are fundamentally important to ecosystems,” said Doug Schmidt, a researcher in the lab. “They provide food and shelter to several different types of organisms. If they are lost, the entire ecosystem will be negatively affected.”
According to Palmieri, the symptoms of Sudden Oak Death vary from plant to plant. An oak or tanoak tree infected with the disease will present symptoms such as “oozing out of the trunk” — a canker — on the tree.
Palmieri said that there are two ways to deal with the disease — early prevention and eradication. Early prevention includes root zone management, pruning and proper irrigation of the trees, and eradication is completely removing the infected tree to prevent spread to healthy trees.
In addition to the aerial surveys, researchers could see that the disease had become more widespread this year because of the data collected from Sudden Oak Death Blitz surveys, according to Schmidt.
Schmidt said Sudden Oak Death Blitzes, founded in 2008, are community-based outreach programs coordinated by local organizers in cooperation with UC Berkeley, and the programs are endorsed by the U.S. Forest Service, the Gordon and Betty Moore Foundation and the National Science Foundation.
The volunteers in the program — referred to as “citizen scientists” — are trained to identify disease symptoms in different plants, and every spring for two days, they survey the land in their areas and collect samples of leaves that present symptoms of Sudden Oak Death. The samples are then sent to Garbelotto’s lab to be analyzed for the disease.
Schmidt said that this spring, a total of 10,000 trees were surveyed in 19 Sudden Oak Death Blitzes organized throughout Northern California by more than 500 volunteers.
Debbie Mendelson, a member of the county of Woodside’s Conservation and Environmental Health Committee, said she joined her local Sudden Oak Death Blitz because she read an article about Sudden Oak Death and its harmful effects on the environment, and from her own experiences, she wanted to raise awareness of the disease.
“There was a tree on my property that I had walked by every day until one day I noticed it had what looked like wood shavings near its trunk,” Mendelson said. “After having someone come to check it out, we found out that it was positive for (the disease). It was healthy for two years before finally becoming brittle, and I was forced to cut it down.”
The disease is currently found in the wildlands of 14 coastal California counties, from Monterey to Humboldt, according to Palmieri, and more counties are likely to be affected by the disease if preventative measures are not taken.
“Last year, the Contra Costa County was really affected by SOD, and it seems to be moving into the urban areas in Alameda County,” Garbelotto said. “It’s time for them to do something to prevent the spread of this disease, or they will, unfortunately, face the same troubles.”
Schmidt said that so far, samples taken from campus have tested negative for the disease, but without preventative measures, that could soon change.
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