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Northern California's Endemic Sudden Oak Death
Many Northern California Residents Are Dealing With an Exotic Disease that Targets Mature Oak Trees.


A leaf displaying the devastating effects of Sudden Oak Death.

For many Northern Californians who reside along the coast, the battle against Phytophthora ramorum, or Sudden Oak Death (SOD), is a relatively new problem. The first reported findings of the pathogen in the U.S were in 1995, as researchers noticed large amounts of mature oak trees in Northern California dying spontaneously. Since then, the disease has been observed as having devastating effects in Great Britain, Germany, southern Oregon, and many parts of Northern California.

Phytophthora ramorum is a pathogen that is commonly found in areas along the coast that have cool, damp, foggy environments with a high density of trees. The beginning signs of SOD can vary from tree to tree, and the website for California's Oak Mortality Task Force states that the only way to be certain that a plant has this disease is to have a tissue sample laboratory-tested. However, before a laboratory sample is necessary, many trees infected by SOD will display signs of the infection, which might include: development of cankers on the trunk, seepage of dark-black or amber colored sap, fractured bark around the base of the tree, and complete wilting or browning of the foliage. It is important to note that at this time there is no viable cure for the disease, and only preventative measures can help stop further spreading.

While researchers have a good idea about what sudden oak death is, there are still many unexplained aspects, such as its origin, exactly how it spreads, and a cure for the bacterium. What experts do know is that SOD affects many types of trees, such as Douglas firs, Holm oaks, and even coastal redwoods, although various species of oak trees are the most susceptible to wilting and death. (A complete list of susceptible species is available on

Some cities have begun to take preemptive measures in an attempt to combat the spread of Sudden Oak Death. Dave Dockter, the environmental planner and arborist for the Urban Forestry Group in Palo Alto, California stated, "The city of Palo Alto applies SOD precautions to all development related entitlements." Furthermore, the city has included an addendum in its Tree Technical Manual, entitled Sudden Oak Death Best Management Practices, in which it "requires that all contractor activities and delivery vehicles perform the work according to the county quarantine restrictions" whenever dealing with the virus. These restrictions exemplify the on-going problem that SOD currently poses to many communities across the state.

Many arborists believe that SOD spreads more during a winter with heavy rainfall, as the pathogen may be carried in water runoff from tree to tree. Another hypothesis suggests that humans are the transmitter of the microorganism, as Phytophthora ramorum is perhaps carried from one area to another by landscaping equipment. Yet, no matter the causation, once a tree is infected by sudden oak death, it will typically die within two to four weeks. Some species of trees, such as the coastal redwood, are more likely to recover, however, recovery among oaks is very rare.

Luckily, the pathogen is not able to infect humans, and may not necessarily spread to every adjacent oak tree. If you feel that you are experiencing problems with SOD it is advised that you contact your local forestry agent to ensure proper precautions are followed. A list of available contacts is provided on under the contacts quick link found on the right side of the home page.

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November 18, 2019, 11:02 am PDT

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