The Park has been monitoring and sampling for Phytophthora ramorum (the pathogen that causes SOD) since 2003; however, this is the first time it has been confirmed on the grounds.
Responding to a request from the Presidio Trust, the federal agency that manages the interior 80 percent of Presidio lands, Matteo Garbelotto of UC Berkeley’s Forest Pathology and Mycology Laboratory sampled the symptomatic tree and determined that it was infected with a strain of the pathogen that is typically associated with nurseries.
Ornamental plant may be source of infection
“This finding suggests the source of the Presidio infestation may be an infected ornamental plant. While a relatively uncommon event, the fact that nursery plants can still be a source of infection is an issue affecting not only California but also other states in which the SOD pathogen has only been found in nurseries but not in the wild,” said Garbelotto.
“I was surprised by the finding because the Presidio is located in an urban setting, far from any other known infestation,” continued Garbelotto. “With a few exceptions, all known infestations are close to oak woodlands or redwood forests.”
Additional inspections of the site show no other sign of infection. The finding is not a likely source of further infection as P. ramorum is not spread by infected oak trees, but rather by spores produced from infected hosts that contract leaf and twig infections such as bay laurel, toyon, and rhododendron. The Presidio Trust and Garbelotto continue to monitor the Park, in an effort to insure no further infections are present.
A comparable situation was reported several years ago in Golden Gate Park, but at that site, infected California bay laurel and oaks were found in close proximity to an area where rhododendrons were held before being planted throughout the park. With bay laurel and rhododendron leaves supporting pathogen sporulation, there was a clearer picture of the pathogen’s path.
“Here at the Presidio, we found toyon near the oak,” Garbelotto said. “Toyon is a native California species that can become infected and potentially spread the disease to oaks. Currently these toyons are healthy. Our best guess at this time is that the oak was infected in 2006; hence the toyons may have been temporarily infected at that time, but lost their infection because of the 2007-2009 drought.”
Securing the site
Upon confirmation of the pathogen, Presidio personnel took steps to secure the site, which now has fencing up around the oak, preventing foot traffic from moving soil and plant material directly beneath the tree to other areas. Signs have also been posted near the infested site informing visitors of measures they can take to assist in prevention efforts.
“We’re doing all we can to prevent the spread of SOD in the Presidio’s forest, including ongoing testing in the area and educational outreach with Park neighbors and users,” said Christa Conforti, integrated pest management manager for the Presidio Trust.
The Presidio Trust will be conducting a “SOD Blitz” April 29 to May 2, 2011, when hundreds of samples will be taken throughout the Presidio and vicinity. Training for the community/Presidio-based cooperative effort to sample for the pathogen will be provided by Garbelotto on Friday, April 29, 2011. Residents near the Presidio have been invited to participate in the training as well as follow-up sampling efforts on their properties.
For more information on Sudden Oak Death, contact Katie Palmieri at (510) 847-5482 or go to the California Oak Mortality Task Force website at http://www.suddenoakdeath.org. For more information on the SOD Blitz in the Presidio, contact Presidio Trust Public Affairs at (415) 561-5331.