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Californians urged to help reduce spread of Sudden Oak Death

July 16, 2007

An update on the increased spread of Sudden Oak Death, a plant disease devastating many of California's coastal oak and tanoak trees, and information on what Californians can do to help reduce its spread will be presented during a news conference on plant diseases that are of importance to California's economy and agriculture. The news conference will be held Monday, July 30 at 11 a.m. PST at the Town and Country Resort and Convention Center in San Diego, Calif.

Sudden Oak Death is caused by the pathogen Phytophthora ramorum. P. ramorum also manifests itself as a foliar or twig blight on more than 100 known plant species, including Douglas-fir, coast redwood, and numerous ornamentals, such as rhododendron and camellia. Unlike Sudden Oak Death, the foliar and twig blight rarely causes the host plant to die. Instead, many of these hosts allow spores to build up on leaf and twig surfaces, thereby facilitating pathogen spread. These ornamental hosts have been found in P. ramorum-positive nurseries throughout the U.S. and other countries.

Although California has lost more than a million trees and at least another million are currently infected, only 10.5 percent of the state's forests considered at risk for pathogen establishment are currently infested.

"There is still a lot of land out there for us to protect and an early detection, eradication, and containment program will help us accomplish this," said Susan Frankel, Sudden Oak Death Research Program Manager, USDA-Forest Service, Pacific Southwest Research Station.

To help protect areas not yet exposed to the pathogen by inadvertently planting infested ornamentals, landscapers and homeowners should carefully inspect host plants before making a purchase to be sure they look healthy and are free of browning leaf tips or edges. After purchasing a P. ramorum-susceptible plant, it should be kept in an isolated area outside for eight weeks before planting to be sure no disease symptoms appear. Host plants should not be planted near susceptible oaks and tanoaks.

People visiting areas known to be infested should comply with state and federal regulations by not removing any host material from the site, including firewood. As an added measure of caution, visitors should remove all organic material from shoes, equipment, tires, pet's paws, and other surfaces before leaving an infested area to help ensure that they aren't accidentally taking the pathogen with them to their next destination.

New DNA research has enabled plant pathologists to identify three lineages of P. ramorum. "By being able to track which lineage is found we can better track where infested material is coming from, track the spread patterns, and be aware of the presence of different lineages in a single location, which is cause for concern over the different lineages potentially mating," Frankel said. More information is available at www.suddenoakdeath.org.

American Phytopathological Society