UC Berkeley researchers find sudden oak death in California spreading south

SOD Blitz/Google Earth Map/Courtesy

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Recent campus findings reveal that a pathogen that kills oak trees by the millions has recently spread further down the coast of California than ever before.

The pathogen, which can cause Sudden Oak Death, has been the focus of research team SOD Blitz — part of the UC Berkeley Forest Pathology and Mycology Laboratory — for a decade. Its research, announced Sunday, included DNA sampling revealing that the disease has reached the San Luis Obispo region for the first time.

The pathogen, called Phytophtora ramorum, has killed more than three million native oak and tanoak trees in California since its initial detection in early 2000. It thrives in environments with moist, humid and mild conditions.

“The pathogen spreads only when it’s raining. During the drought, it wasn’t spreading very much,” said principal investigator and adjunct professor Matteo Garbelotto. “However, when it started raining, some infections doubled compared to last year (and) in some locations it’s four to five times as much.”

The pathogen poses a domino effect as it also harms various plants besides oaks, including keystone plant species. The death of important plant species susceptible to the pathogen could pose a much larger negative impact on other wildlife as a consequence, Garbelotto said.

The research is a collaborative effort between volunteers and scientists, known as “citizen science.” The survey and sample data was collected by volunteers and then analyzed for genetic testing by the campus lab.

In 2016, SOD Blitzes held 23 meetings across California from Mendocino to San Luis Obispo, where about 500 volunteers participated to survey the state’s natural habitats and collected samples in search of the invasive pathogen in oak trees.

“Thanks to the help of citizen science volunteers, we are able to monitor a lot more of the national landscape than we would have been able to otherwise,” said Katie Harrell, communications director of the California Forest Pest Council. By knowing where the pathogen is and isn’t, or at least by attempting to identify the location of the pathogen, we can be much more proactive in containing the disease.”

There is no guaranteed cure for combating the pathogen, Harrell said, but there are preventative measures that can be taken.

“A lot of factors go into play and preventative treatment is useful, but if the tree is really susceptible and conditions are favorable for the pathogen then it can be affected in ways,” Harrell said.

Besides the economic and ecological ramifications that the disease imposes on the equilibrium of the ecosystem, it also poses a concern for Californian indigenous tribes who hold practical and symbolic value for oak trees, according to Mike Grone, a campus fourth-year doctoral student in archaeology.

“Many native groups used fire for controlled burns around the base of oak trees in order to kill off pests eating the fallen acorns, while returning nutrients to the soil in the form of nitrogen-rich ash,” Grone said in an email. “These trees and the acorns they provide continue to be important to Native peoples to this day as a food source as well as for spiritual and cultural purposes.”

Contact Mariah De Zuzuarregui at [email protected] and follow her on Twitter at @mdezuzuarregui.