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Sudden Oak Death (SOD) Overview

Sudden Oak Death (SOD) is a disease that infects and kills certain oak tree species. SOD has killed many trees in Vista Verde and the surrounding area and continues to spread. This article discusses SOD and how it can be prevented. The Vista Verde/Los Trancos Woods Sudden Oak Death (SOD) Task Force was formed to help minimize the effects of SOD in our neighborhood by educate homeowners and identifying best practices. The SOD Task Force is headed by Amanda Lee and has compiled the information below.

What is SOD?

Sudden Oak Death (SOD) is a tree disease that kills some oak species and has had devastating effects on forests in California, Oregon, and Washington, where it has killed more than a million oaks since the mid-1990s. SOD is widespread in the Corte Madera and Los Trancos Creek watersheds, which includes our neighborhood, and has killed a large number of trees in both Vista Verde and Los Trancos Woods. Four local varieties of oak and tanoak are susceptible to SOD.

SOD is caused by the plant pathogen, Phytothera ramorum, which is a water mold that spreads during wet weather using host plants such as Bay Laurel. Although P. ramorum does not kill the host plants, it causes leaf spots or browning. Red sap leaking from lesions in the lower trunk often precedes the sudden death of affected trees.

Are My Oak Trees At Risk?

If your trees are species susceptible to Sudden Oak Death and you live near where trees have already succumb to the disease, your trees are at high risk. Only two common oaks in the area are susceptible: the Coast Live Oak and the Black Oak. Less common, but also present in are neighborhood, are the Canyon Live Oak and the Tan Oak. Valley Oak is not susceptible. Please use the oak identification sheet as a guide in determining what type of oak you have.

SOD can be spread from one susceptible oak to another, but it is often spread by non-oak carrier species listed here. Among the most common of these carriers in our area is the bay laurel tree, which has been termed the “Typhoid Mary” of SOD.

Most of the trees that have died or become infected are in an area extending from Corte Madera Creek up hill to Old Spanish Trail and the higher areas of Vista Verde, or are near the Los Trancos Creek in the East. Unfortunately, the fungus-like “water-mold” that causes SOD is wide spread in our community so all susceptible species of oaks, regardless of location, are at some risk. The Sudden Oak Death Task Force has mapped the progression of the disease in Vista Verde and Los Trancos Woods.

How Do I Prevent My Oaks From Getting SOD?

There are two methods two that seem to work well to protect neighborhood oaks from Sudden Oak Death. Our Sudden Oak Death task force, and most professionals working in the field recommend that the methods be used in combination where possible. The two methods are:

  1. Trim back your Bay trees and other carrier plants according to these guidelines.
  2. Apply Agri-Fos according to these guidelines. Agri-Fos is phosphate compound formulated to stimulate growth in trees, improving their defenses against SOD and other pathogens.

Sudden Oak Death Web Sites

County SOD Resources

Contact: Jeremy Eide, San Mateo County Agriculture, Weights & Measures, 728 Heller Street, San Mateo, CA 94064-0999, 650-363-4700, jeide@co.sanmateo.ca.us

Jeremy will come to your property to take samples from oak trees suspected of having SOD for positive identification of the SOD phytophthora. It takes 3 – 4 weeks to get test results. Call or email him for an appointment.

You can also bring host tree leaf samples to Jeremy at his Heller Street address. Please bring at least 10 leaves per tree that were picked within the last 24 hours. He will send to lab for positive identification of the SOD phytophthora. It takes 3 – 4 weeks to get test results.

All above is free of charge.

Bay Laurel and Oak Disposal

Once SOD-infested oaks, bay laurels, and other trees are taken down, that material is still capable of infecting living trees. Recommendations for disposal of SOD-infested material found on www.suddenoakdeath.org website from the “Homeowner’s Guide” (http://nature.berkeley.edu/comtf/pdf/HomeownersGuide6-07.pdf ) are:  “In infested areas where burning is not possible, the best option is to leave infested material on site, chipping the small material (for use as ground cover) and using larger pieces for firewood. Composting can also successfully kill the pathogen, but the compost must reach temperatures that are probably not possible or practical in a home composting site. Since inoculum levels are already thought to be high in an infested site, leaving the additional inoculum from the infested plant material on site will not significantly worsen the local disease conditions.” 

I remember Matteo Garbelotto (the main speaker at the August 2nd SOD Forum in Woodside), in answer to my question asking the very same thing, recommended homeowners cut up or chip Bay Laurel branches and leave them on their property in a sunny location as far away from SOD susceptible oaks as possible.  I understood him to say that the heat from sun exposure tends to kill or diminish the pathogen over time.  Only the Bay leaves host the pathogen.  When the pathogen is on the ground (as opposed to above via live bay branches) it is much less able to travel to the trunk of the oaks and thereby infect them; the pathogen does not seem to infect the oaks via their root system.  Matteo also said that putting bay laurel debris in GreenWaste yard trimming collection pickup is a very good option since GreenWaste’s composting is regulated and attains the required heat to kill the pathogen.  The amount of debris may make this too difficult for some to accomplish.

When moving cut bay branches, try to avoid dragging by your oaks.  This is not always possible of course.  I have wrapped a few oak trunks that I know will come into contact with branch removal with visquine/plastic I had on hand (could use a tarp or whatever).  Just be sure to toss or disinfect when you’re done.  This is purely my idea, so take it with a grain of salt – I figured it couldn’t hurt.

Oak disposal is different than Bay Laurel disposal.  Oaks (other than Tanoaks) are not foliar hosts and they cannot infect other oaks with SOD.  Oak wood can be saved, set in a sunny location to dry and later burned as firewood (as could Bay Laurel wood, though I don’t know how well it burns).  Branches can be chipped and disbursed locally or within the 14 designated counties that are experiencing SOD.

It is important to clean equipment used in order to reduce the spread of the SOD pathogen.  Guidelines for cleaning equipment such as chainsaws, clippers, chippers, boots, etc. can be found also at www.suddenoakdeath.org with their write up “Sanitation Measures to minimize pathogen spread” that can be found by following this link:  http://nature.berkeley.edu/comtf/pdf/Professional%20sanitation%20guide.pdf .

I recommend looking at the www.suddenoakdeath.org site to educate yourselves further about SOD.  I am simply passing along information that I have found on that and other reputable sites.