The Blitz aims to wipe out sudden oak death

Debbie Mendelson looks at a diseased bay laurel tree leaf in Woodside on May 10. Photo by Magali Gauthier/The Almanac

Debbie Mendelson is a zealot for saving oak trees from sudden oak death (SOD), a scourge that has wiped out millions of trees in recent years.

Mendelson is the chair of the Peninsula version of "The SOD Blitz," which will take place in Portola Valley on May 18.

During the Blitz, volunteers go out into the oak forests and take leaf samples that are sent to a lab at University of California at Berkeley to find out if the samples show evidence of sudden oak death.

The Blitz started on the Peninsula and in three additional California communities in 2008 and has now spread to 27 locations in the state, Mendelson said. The Peninsula Blitz is now held annually and alternates between Woodside and Portola Valley.

"It's the largest citizen science program in the world," she said.

Sudden oak death is a forest disease that infects trees such as tan oak, coast live oak, Shreve's oak, California black oak and canyon live oak, she said.

The oak trees get infected in the trunk and die by degrees over two to three years, she said.

Many of the local participants check the trees in Huddart Park and ones on their own properties.

"Way back in the beginning when I had an adolescent oak on my property, I witnessed what is sudden oak death," Mendelson said. "All the leaves on the tree seemed to turn brown overnight."

Matteo Garbelotto, director of the forest pathology and mycology lab at UC Berkeley, was on the team that first isolated the microbe that causes SOD.

The researchers found that the pathogen originated in ornamental plants that had arrived from Asia, including rhododendrons and camilla, and had escaped into the larger environment, Garbelotto said.

The phenomenon happened first in California, but there have also been recent sudden oak death outbreaks in England, Belgium, Holland, Ireland, France and southern Oregon, he said.

The tree that spreads SOD to the oaks is the bay laurel, which can grow beside oak trees and at times become intertwined with them, he said.

"The way to slow down the disease is to find a way to reduce the number of bay laurel," Garbelotto said. "Also, if we can increase the distance between the oaks and the laurel, the range that the disease can spread goes down."

Participants collect samples from the bay laurel since it is much cheaper and easier to test the disease carrier than to test the oaks, Garbelotto said.

The infection rate for oaks within 15 feet of a bay laurel tree is about 75 percent, he said. After a distance of about 20 yards the infection rate drops substantially.

After the samples are gathered, they are shipped to Garbelotto's lab where they are evaluated using DNA tests, Garbelotto said. Test results are then published online at

"If an infected oak is near your house, you want to take it out because if it burns in a fire it will spread to your home," he said.

The spread of sudden oak death is more rapid during wet weather, so organizers are expecting more infections after this year's rainy winter, he said.

This year's Peninsula SOD Blitz will start at the Portola Valley Town Center, 765 Portola Road, beginning at 10 a.m. For more information, contact Woodside Town Manager Kevin Bryant at 650-851-6790.

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