New Study Aimed at Protecting Canyon Live Oaks

P. ramorum symptoms on California bay leaf

Sudden oak death (SOD), caused by the water mold Phytophthora ramorum, is killing oak and tanoak trees throughout coastal California and Oregon. The California bay tree has been identified as a main transmitter of sudden oak death, because it hosts the pathogen on its leaves but does not die from it. P. ramorum spores spread from bay leaves to nearby oak trees, which become systemically infected and die.

Scientists have recently disocvered that Los Trancos Open Space Preserve may be the only known site where mature canyon live oaks are dying from sudden oak death. It was previously thought that mature canyon live oaks were not affected by this disease. The Open Space District and scientists are working quickly to try and confirm this, while protecting these and other large oaks with a new study that began in November 2009.

Large, healthy canyon live oaks in Los Trancos Open Space Preserve

In Los Trancos Open Space Preserve, twelve large oak trees along the Fault and San Franciscan Loop trails were sprayed with the fungicide Agri-Fos, considered by the EPA to be safe and non-toxic. Scientists believe Agri-Fos may help protect healthy oaks from sudden oak death. The trees will be sprayed again in spring 2010 and then annually each fall. Select California bay trees near the treated oaks will be removed to reduce the risk of infection.

As part of this same study, bay trees will also be removed from around large canyon live oaks along the Ancient Oaks Trail in the Russian Ridge Open Space Preserve. Scientists are concerned that visitors climbing these oaks may be contributing to sudden oak death infections due to P. ramorum spores on their shoes being transmitted directly to the tree trunks.

Ongoing Sudden Oak Death Research on District Lands

The District has been recognized by researchers worldwide for its contributions to the science surrounding this disease, which currently has no cure. In 2005, the District committed more than $150,000 over 10 years to research the prevention and treatment of sudden oak death. There are currently several ongoing sudden oak death research projects on District land conducted in partnership with scientists from UC Davis, UC Berkeley, the US Forest Service and Phytosphere Research.

These studies attempt to identify tanoak trees that are genetically resistant to SOD, prevent infection of large specimen trees, and determine whether the use of Agri-Fos, coupled with selective California bay tree removal, is effective in protecting select specimen trees and large stands of oaks from sudden oak death. Results from these studies contribute to finding a long-term solution to sudden oak death and help the District preserve a healthy natural environment and provide beautiful recreational areas for future generations to enjoy.