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Sudden oak death disease spreading in Napa County

Sudden oak death disease spreading in Napa County


The results are in and the news is not good. Sudden oak death, the disease that has been killing countless oak trees is spreading, and new portions of Napa,  both city and county, have just been confirmed as infested.

In cooperation with the UC Berkeley Forest Pathology and Mycology Lab, volunteers participated in the 2011, SOD Blitz, a collaboration of university research scientists and volunteers from numerous counties in California, to locate and fight this devastating disease.

This is the first year Napa has participated in the program, which is now in its fourth year.

 On June 4,  about 20 volunteers attended a meeting at Skyline Park to receive training and sample collection packets from UC researcher Doug Schmidt. We then headed out to our chosen locations to collect California bay laurel leaves showing  symptoms of the disease. Then, on June 6, I delivered the sample packets to the UC Berkeley lab.

The results were made public on Oct. 2 and can now be viewed on the lab website:

The 2011 SOD Blitz, held in 13 regional locations, shows an overall dramatic increase in confirmations of the disease. The worst hot-spots were Saratoga/Los Gatos, Woodside/Portola Valley, and Marin, followed closely by Sonoma, Napa, and Atherton/Palo Alto/Menlo Park. 

Since the disease is dependent on water, it is believed that a recent increase in lingering spring rainfall has fostered the increase in the disease.

Here in Napa, 137 samples were collected, resulting in 34 positive tests for Phytophthora ramorum,  the organism that causes the disease.

A close look at the Napa County 2011 SOD Blitz results on the website’s Google Earth map reveals that the disease is present in a wider geographical distribution than was previously thought. SOD has been regarded primarily as an inhabitant of  outlying densely forested areas,  a few of the 2011 Napa results show it is present in and near the city: A location on Napa Creek at California Boulevard, Merced Street (a few blocks south of Pueblo Avenue), and near Carol Drive.

Other newly confirmed locations are in the classic wooded habitat for the disease such as portions of Redwood Road, Dry Creek Road and the mountains west of St. Helena, with a surprising one on the east side of the valley on Soda Canyon Road.

Checking the newly confirmed locations on a Napa road map, I find that virtually all of the city of Napa is within a three-mile radius of a confirmed site.  That is the distance within which the California Oak Mortality Force Arborist Guidelines recommend that tree owners seriously consider risk factors and protection measures for healthy, high value oaks.

Bill Pramuk is a registered consulting arborist. Visit his website,, email questions to or call him at 707-226-2884.

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