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Sudden Oak Death

OPB | Oct. 6, 2006 10 a.m.

Trouble is brewing in Oregon’s southwest coastal forests in the form of Phytophthora ramorum, a deadly microbial pest that could devastate woodlands throughout the state. Oregon considers the threat from Sudden Oak Death so serious that they are taking drastic measures in response to each positive sighting. If Sudden Oak Death goes unchecked, it could cause significant damage to Oregon’s forest ecosystems.

First Broadcast: 2006
Producer: Ed Jahn

Frequently Asked Questions about Sudden Oak Death

Despite their aggressive efforts, many Oregon officials are concerned that the disease will eventually elude their grasp and spread to other parts of the state. One key defense is an informed and vigilant public. We’ve compiled some basic information about Sudden Oak Death (SOD) and how to identify its symptoms.

What is Sudden Oak Death?

Tanoak mortality on Mt. Tamalpais, Marin County. Photo courtesy of Borys Tkacz, USDA-Forest Service.
Sudden Oak Death (SOD) is a forest disease caused by the plant pathogen Phytophthora ramorum. Known susceptible plants include tanoak, coast live oak, Shreve’s oak, California black oak, canyon live oak, and sometimes madrone. There are two categories of hosts for Phtophthora ramorum: bark canker hosts and foliar hosts. The bark canker hosts are tanoaks and oaks that become infected on the woody portions of a tree. Cankers on the trunk of these trees are the most damaging, and often lead to death. Additionally, diseased oak and tanoak trees are often attacked by other organisms once they are weakend by P. ramorum. These secondary invaders can also kill the tree, and include such organisms as Hypoxylon thourasianum (a fungus that decays sapwood) and bark beetles. In foliar and twig hosts, symptoms can range from leaf spots to twig dieback but these hosts rarely die from the infection.
What is Phytophthora ramorum?

Tanoak bark bleeding. Photo courtesy of Karl Buermeyer, UC Cooperative Extension
Phytophthora ramorum is a plant pathogen that causes Sudden Oak Death as well as a foliar/twig disease in other susceptible plants. Both bark canker and foliar hosts act as a breeding ground for the disease, allowing inoculum to build up on leaves, and then spread to new areas via natural or artificial means.
Where has Phytophthora ramorum been found?
Natural areas found with infection have been along the northern and central coast of California, as well as near Brookings in southwest Oregon. In addition to natural infection in woodland and forested areas, Phytophthora ramorum has also been found in the nursery system on host and associated plants.
Can the plants and trees in my yard get Sudden Oak Death? What should I look for?

Leaf spots on rhododendron. Photo courtesy of Shane Sela, Canadian Food Inspection Agency (CFIA)
Before you start to panic and head out to your garden with a chainsaw, it is important remember that occurrences of SOD in Oregon are still relatively isolated. Wild occurrences of the disease remain contained to a 22+ square mile quarantine area outside Brookings in southern Oregon. However, a number of common garden plants such as azaleas, red oaks and Rhododendron are susceptible to the disease. Despite mandatory inspections at nurseries, there is a possibility that SOD could be spread to other parts of the state through nursery stock. Also, keep in mind that many other organisms and injuries can produce symptoms similar to SOD. The only way to be certain that a plant has Phytophthora ramorum is to have a tissue sample laboratory-tested. However, there are some steps that can help you determine if Sudden Oak Death is likely:
  • Determine if have any susceptible species. The California Oak Mortality Task Force maintains a list of hosts and associated hosts. Because this is a relatively new disease, the host list continues to grow as further research is conducted.
  • Check to see if you are in a currently infected area. While you may have plants that are found on the host and associated list, it is important to determine if you are in an area that is currently infested and conducive to pathogen activity. This will assist you in determining the level of risk to your plants. If you are outside of an infested area, your tree could still have Sudden Oak Death, but it would be less likely.
  • Inspect your trees and plants for symptoms. Become familiar with the symptoms of SOD and compare them to those on your oak tree or plants. If you find symptoms, check other susceptible tree and shrub species nearby. Do they have symptoms of P. ramorum infection? Keep in mind that a number of other plant diseases show similar symptoms. The Oak Mortality Task Force has a diagnostic guide which can help you determine the likelihood of SOD. Also, check out their misdiagnosis page for other diseases which can be mistakenly identified as SOD.
Who do I call if I think I suspect Sudden Oak Death is present in my plants or trees?
Your local county office of the Oregon State University Extension Service is prepared to answer your questions about SOD, tell you how to take samples for testing and guide you to additional resources. You can find the number of your local office in the county listings of the phone book. The OSU Extension Service website also has a list of county offices and is good source of information and resources.

The information and photos on this page were adapted from the California Oak Mortality Task Force website.

More Information
California Oak Mortality Task Force Website
  • The Oak Mortality Task Force was set up as “the” resource for information about Sudden Oak Death. Their website provides abundant photos, reports, maps, research papers, publications…you name it. If you can’t find it on their site it probably doesn’t exist.
  • Online: None
Sudden Oak Death in Oregon
For questions about SOD in forests:
  • Contact: Everett Hansen, Oregon State University
  • Phone: 541-737-5243
For questions about SOD in nursery plants:
  • Contact: Jennifer Parke, Oregon State University
  • Phone: 541-737-8170

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Major Support Provided By:

  • Dorothy D. Gage and Dan Stanton

Additional Support Provided By:

  • Kay Kitagawa and Andy Johnson-Laird
  • Christine and David Vernier
  • Coit Family Foundation
  • Greenfield/Hartline Habitat Conservation Fund of the Nature Conservancy
  • Lois E. Jones
  • Bonnie and Peter Reagan