April 14, 2018
In 2016 we had to have seven stately 100-year-old coastal live oak trees on our property in Inverness cut down due to sudden oak death (SOD). This sad fact fits into the data from SOD Blitz, a project of the Univerity of California at Berkeley forest pathology and mycology laboratory — that SOD has killed hundreds of thousands of coastal live oak and tanoak trees in Marin and other coastal communities in California and Oregon. In fact, in the past year, the largest sampling of affected trees by SOD Blitz volunteers showed that the incidence of SOD statewide is three times higher than it was two years ago. In Marin, the overall infection rate in 2017 was estimated to be just above 21 percent, an increase of 5 percent from 2016.
The SOD Blitz program was instituted by Matteo Garbelotto, the director of the laboratory, in 2008 as an effort to track the devastation affecting coastal live oaks and tanoaks (sodblitz.com). For the 2017 blitz, 315 volunteers surveyed nearly 15,000 trees by submitting leaf samples from approximately 2,000 symptomatic trees from Siskiyou County in Oregon south to San Luis Obispo County. Now with almost 10 years of data, the current detailed 2017 map of areas devastated by SOD documents the epidemical spread of the disease in the state.
Training meetings for volunteers are on a Friday evening or Saturday morning, and last one hour. Armed with collection materials, these newly branded citizen scientists go out on the weekend following the training into their locales to collect leaf samples, tag bay trees that exhibit symptoms of infection and, using GPS, record the location of affected oaks. Leaf samples are bagged and brought to Garbelotto’s lab for analysis. Results from each year’s survey are added to that year’s SOD map so volunteers can track the results of the trees sampled in their area. These blitz surveys, conducted each spring, educate participants and help scientists identify mildly affected areas where proactive management may be crucial.
Of major concern since the outbreak of fires in Sonoma last October is the finding that oak trees killed by SOD ignite easily and burn extremely hot. This is scary news for Marin homeowners concerned about the heightened risk of wildfires in Marin. To add to the growing alarm, Garbelotto says another finding of concern in this year’s survey is that SOD has spread into some more populated urban areas of Marin such as Ignacio, Greenbrae, Kentfield and Mill Valley. This suggests that Marin residents would be wise to take preventive action, such as attending a SOD Blitz to learn how to monitor trees on their property and identify infected bay laurels particularly those near high-value oaks. Other actions include removing dead oaks and other combustible material.
SOD was identified in 1995 in West Marin by Pavel Svihra, a former UC cooperative extension advisor. During wet, warm weather spores of the pathogen, Phytophthora ramorum, a fungus-like “water mold,” are airborne, allowing the infection to spread via water droplets from California bay trees that sit close to coastal live oaks and highly susceptible tanoaks. Often the first sign of infection is a discoloration on the tips of California bay laurel leaves. As the infection progresses, the pathogen cuts off nutrients and water gradually killing the oak. Symptomatic oaks exude a dark sap from their trunks. There are no known methods to arrest the spread of the disease once trees become infected. Applying a preventative phosphonate to oaks at risk in the fall is currently the recommended treatment.
The next SOD Blitz training in Marin is from 10 to 11 a.m. May 5 in room 103 in the Joseph R Fink Science Center at Dominican University of California at 155 Palm Ave. in San Rafael. Help protect your property and Marin’s forests and landscapes — volunteer to help researchers monitor and ultimately control this disease. To register, contact Wolfgang Schweigkofler at firstname.lastname@example.org.