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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, This email address is being protected from spambots. You need JavaScript enabled to view it.

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.