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Forest Products Extension

Sudden Oak Death

Tennessee is one of the nation's largest producers of hardwood lumber and much of that output is white and red oak. So the news of a contagious disease that is killing oaks in California is certainly a cause for concern. The good news is that the pathogen has not spread to the forests of Tennessee . The bad news is that the disease has been detected in Tennessee plant nurseries and it appears to be adaptable and difficult to contain.

Sudden Oak Death (SOD) is the name that has been given to the various tree and shrub diseases caused by Phytophthora ramorum . This fungus-like organism, a relative of the blight that caused the Irish potato famine, has more than 60 known host plants in the United States , mostly in the coastal regions of Northern California and southern Oregon . SOD has killed tens of thousands of oaks on the coast of California and in southern Oregon .

Because SOD can kill its hosts and can infect both ornamental shrubs and forest trees, aggressive quarantine measures have been taken to contain its spread. Infected forest areas and nursery stock have been cut and burned. Nurseries in affected areas in California must have inspections of all known Phytophthora ramorum host plants before they can be shipped around the country .

SOD causes leaf blight, tip dieback and bleeding cankers on infected trees and shrubs, but these symptoms are similar to those caused by a number of other diseases such as bacterial wetwood, anthracnose and other fungal pathogens. Laboratory tests are required to confirm that a plant is infected with SOD. Phytophthora ramorum only infects plants and it is not harmful to humans or animals. It appears that SOD is often unable to spread from trees to other trees; an alternate host understory plant such as rhododendron or laurel may be required to complete the lifecycle of Phytophthora ramorum. However, once infected, the disease can be deadly for trees and there could be serious consequences if this disease spread into the oak forests of Tennessee .

Sudden Oak Death got its name because it has killed many tanoaks and oak species native to California . Other oaks such as the white oaks and red oaks that are so abundant in Tennessee are not yet known to be natural hosts for the disease; however, they have been successfully infected in the lab. Because of a number of factors including a humid climate, a large number of plant nurseries and the presence of potential host plants, Tennessee is considered to be an area at high risk for SOD.

It is too early to tell the impact of SOD on the forests of Tennessee . Monitoring programs are underway throughout the region to detect Phytophthora ramorum. In the meantime , we will have to hope that containment efforts are successful and that SOD doesn't find the forests of Tennessee to be a suitable home.

Go to this site for more information on SOD

Adam M. Taylor
Tennessee Forest Products Center
2506 Jacob Drive
Knoxville, Tennessee 37996

Phone: 865-946-1125
Fax: 865-946-1109

Adam Taylor's email