Sudden Oak Death Science Symposium Held in Monterey

Oaks ’n’ Folks – Volume 19, Issue 1 – February 2003

On December 17 and 18, a Sudden Oak Death Science Symposium was held in Monterey. This Conference was sponsored by the USDA Forest Service Pacific Southwest Research Station and the University of California Integrated Hardwood Range Management Program. It was designed to bring together the broad array of researchers, regulators, and affected industries from throughout the world addressing this new disease, in order to share information and describe the most recent research advances. It featured 40 formal presentations, as well as over 50 posters, and was attended by 300 people from 13 countries and 26 states. It is beyond the scope of this article to describe all of the studies and research results presented at the meeting, but a few of the highlights included:

  • Eight new plant species associated with the Sudden Oak Disease agent, Phytophthora ramorum, were reported, including canyon live oak (Quercus chrysolepis), poison oak (Toxicodendron diversilobum), salmonberry (Rubus spectabilis), cascara (Rhamnus purshiana), California hazelnut (Corylus cornuta), Victorian box (Pittosporum undulatum), Pieris and Western starflower (Trientalis latifolia). Western starflower is the first herbaceous plant to be confirmed as infected with P. ramorum. This brings the total number of confirmed hosts to 21 in California.
  • The strains of P. ramorum found in the United States and Europe are different mating types, suggesting that this disease may not have spread from either of these locations to the other, but likely was introduced to both areas from a third location.
  • California bay laurel (Umbellularia californica) is believed to play a major role in spreading the disease in California since P. ramorum sporulates so prolifically on it. Interestingly, in the infested area in Oregon, U. californica (where it is called Oregon myrtle) is rarely infected.
  • The area found to be infected with P. ramorum in Oregon has, to date, been limited to 30-40 acres in a 9-square-mile region near Brookings, close to the California border. Efforts to eradicate the disease by removing all susceptible hosts in infected areas have so far been successful, though some new infections have been identified in the 9-square-mile area. All infected plants have been destroyed.
  • Over the past year or so, researchers and others surveying for P. ramorum have found another new Phytophthora associated with cankers on oaks and leafspots on California bay laurel. Previously referred to as P. ilicis-like, Everett Hansen and colleagues at Oregon State University are naming it Phytophthora nemorosa. The name won’t be official until validly published in a mycology journal, hopefully sometime in 2003. The name “nemorosa” refers to the woodland habit of the pathogen.
  • In Europe, P. ramorum has only been found on arrowwood (Viburnum spp.), rhododendron (Rhododendron spp.), and Pieris, though there have been extensive surveys to determine if other plants, including oaks, are infected. Most infected plants have been in nurseries and these plants have all been destroyed. Infected plants have been found in Germany, the Netherlands, Spain, Portugal, France, Poland, the United Kingdom, Italy, Sweden, and Belgium.
  • Nine countries now have regulations regarding movement of plant parts from species or genera that have been confirmed as hosts of P. ramorum. These include the U.S., Canada, Germany, the Netherlands, the U.K., Spain, Korea, Australia, and New Zealand. In some cases, movement of soil that is suspected of being contaminated, is also regulated. The European Union also has regulations.
  • Sudden Oak Death is expanding in California, though it is not yet clear whether the rate of spread is increasing or decreasing. Results suggest that the production of spores is related to rainfall, so a recurrence of wet, El Niño conditions could promote an increase in the incidence of the disease. However, it appears that within an infected area, some oak trees are resistant to the disease.
  • There have been some promising results in trials evaluating response of infected oak seedlings, saplings, and mature trees to chemical treatments, suggesting these materials may be helpful in treating trees in a landscape setting. However, no chemicals have yet been registered for treatment of SOD and it is unlikely chemicals could be successfully used in wildland environments.

These are a few of the highlights. To read the abstracts of all of the papers and posters presented at the Symposium, please log on to the California Oak Mortality Task Force (COMTF) web site at: and go to the SOD Symposium web site.

Doug McCreary