Sudden Oak Death, a disease that can destroy oak and tanoak trees in California, has reached "epidemic" proportions in some parts of the East Bay and the Peninsula and prevention efforts against further infestation are "urgently needed," according to an environmental task force.
Surveys of California Bay Laurel trees in selected Bay Area cities, conducted by the University of California at Berkeley and volunteers, show that the pathogen that triggers the disease has spread rapidly in the western East Bay area and the North Peninsula, where "a staggering 48 percent" of bay laurel trees tested in the Burlingame Hills were infected, according to the California Oak Mortality Task Force.
The on-site surveys, known as "SOD Blitzes," of more than 10,000 trees by 500 volunteers identified bay laurel trees with evidence of the pathogen Phytophthora ramorum, which does not harm the bay laurel but can take hold, infect and eventually kill decades-old oak and tanoak trees if left untreated.
"The bay trees are the primary spreaders of the pathogen," said Katie Palmieri, spokeswoman for the task force and UC Berkeley. "They indicate how much pathogen is in the area."
Communities that also have high volumes of infected bay laurel trees -- where spores from the pathogen show up as black and yellow coloring on the trees' leaves -- likely will see their oak and tanoak trees catch the disease as well, Palmieri said.
"The next step is for oaks and tanoaks to be infected" within about a half-mile of infected bay laurels, she said.
Sudden Oak Disease has been killing oak and tanoak trees in the wetlands of California's 14 coastal counties, Palmieri said.
A survey this year by the U.S. Forest Service located 376,000 dead oak and tanoak trees within 54,000 acres in California, up from 38,000 dead trees inside 8,000 acres in 2011, she said.
Leaf samples were gathered from SOD Blitzes last spring in East Bay communities such as Pinole, East Richmond, Kensington, North Berkeley, Claremont and Piedmont.
The samples had pathogen levels so high that infection of oaks and tanoaks in those areas is "extremely likely, making preventative disease management options urgently needed to protect oaks and tanoaks both in private and public spaces," said Matteo Garbelotto, adjunct professor at Berkeley who operates a lab that analyzes the samples.
The elevated levels of bay laurel infection observed in the western East Bay indicate that the disease has "rapidly transitioned from arrival (reported in 2011) to an epidemic phase," Garbelotto said.
The pathogen thrives in moisture and so the wetter the seasons the bigger the outbreaks each year, he said.
"This increase in infection really was predicted two, and especially one, year ago when we had heavier rains and mild springs," Garbelotto said.
"SOD Blitzes, combined with aerial surveys, validate our theory that SOD outbreaks are driven by wetter than average conditions and are initiated by bay laurel infection," he said.
If the disease spreads to an oak and tanoak, two similar but separate species of tree, it creates a dark wound in the trunks of the trees that expands to kill healthy wood, making it harder for the oaks to distribute water and nutrients, Palmieri said.
"It can take several months to several years for them to die," she said. "The tanoaks are the fastest to die."
Volunteers, also known as "citizen scientists," who take part in the SOD Blitz surveys of bay laurels are trained how to recognize diseased trees and to inoculate oak and tanoak trees to prevent the disease from spreading.
The inoculation involves using Agri-Fos, a commercial fungicide that is absorbed into the tree and uses the tree's natural defenses against disease to block the pathogen.
People seeking to protect their oak trees within the half-mile radius of infected bay laurel should consider using Agri-Fos, applied either topically or by injection, into the trees this fall before it gets wet, Palmieri said.
There is no cure once the oak tree is infected, so prevention is crucial, Palmieri said.
"All it can do is help boost the tree's immune system," she said. "As long as you treat a tree before it's been infected, that is the key."
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