Plant Diseases

Updated 07/17/08

Bark displaying Sudden Oak Death symptons Sudden Oak Death Leaves displaying Sudden Oak Death symptons

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State SOD Quarantines (this link goes to a PDF developed by the California Dept. of Food & Agriculture -- it applies to Oregon, California & Washington)

Sudden oak death (SOD) is a serious plant disease that attacks many types of plants and trees common to the Pacific Northwest, including azaleas, big leaf maples, huckleberry, California bay laurel, camellia, myrtles, honeysuckle, Pacific madrone, Douglas fir, rhododendrons, and vibernum. It does not affect humans and is not a food safety concern.

Sudden oak death is caused by a pathogen called Phytophthora ramorum. The pathogen is not a fungus or a bacterium, but a member of a unique group of organisms called Oomycetes. Oomycetes share some characteristics of fungi but are biologically different.

Symptoms of sudden oak death

Symptoms vary from plant to plant, and may include leaf spots, needle and tip blight, shoot-tip dieback, and canker formations. Many other plant pathogens cause the same symptoms. The only way to confirm the presence of sudden oak death is through laboratory testing.

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Sudden oak death discovered in Washington

In June 2003, Phytophthora ramorum, the causal agent of sudden oak death was confirmed for the first time in Washington. Infected rhododendron plants were shipped to a Des Moines nursery from its affiliate in Clackamas County, Oregon. A thorough survey of susceptible plants around the perimeter of the nursery indicates that the pathogen has not moved beyond the nursery.

Since that time the Washington State Dept. of Agriculture (WSDA) has tested over 100,000 plants in hundreds of nurseries as part of the national SOD survey and trace forward surveys from production nurseries found to be infected with the pathogen. Phytophthora ramorum was detected in 24 additional nurseries, all in western Washington. Most of the infected plants were camellias, rhododendrons, pieris and viburnum shipped to Washington retail nurseries from other states.

The United States Dept. of Agriculture (USDA) has issued Emergency Action Notifications to all infected nurseries ordering the nursery to follow the federal eradication protocol.

When the eradication protocol is completed in the nursery, USDA will release the nursery from the federal order. Twenty-two infected nurseries have completed the eradication procedures and are considered free of P. ramorum by USDA. Perimeter surveys from all infected nurseries have been completed with no infected plants detected.

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WSDA placing a high priority on containing sudden oak death

WSDA is doing everything possible to determine the extent of the problem and ways to eradicate or limit the spread of any potential disease. For example:

WSDA is working closely with scientists and regulators from the Oregon Department of Agriculture, the California Department of Food and Agriculture and the USDA Animal and Plant Health Inspection Service (APHIS) to prevent sudden oak death from becoming established in Washington.
WSDA is receiving excellent cooperation with businesses affected by the incident.
WSDA is aggressively pursuing the detection and elimination of infected plants.
WSDA has surveyed 135 Christmas tree plantations and ninety-one sections of forest land.
No evidence has surfaced to suggest that sudden oak death moved beyond the nurseries.

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Two strains of pathogen found

The American strain of sudden oak death was found for the first time in 1995 in Mill Valley, California. Since then, it has been detected in 17 California counties. And in 2001, it was found in Curry County, Oregon near the California border.

The disease has killed thousands of oak and tanoak trees found in California and Oregon. Other plants common to the Pacific Northwest are susceptible to the disease, but are not likely to die.

Since May 2003, the European strain of sudden oak death has been detected in nurseries in Oregon, Washington and British Columbia, Canada, although most infected plants are by the American strain. There is no evidence that either strain has moved beyond the nursery environment.

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The origin of sudden oak death is unknown

Plant pathologists do not know where the pathogen originated, but the disease is spread naturally and artificially. In nature, the pathogen is spread through the movement of water in the form of rain, mist, dew and runoff. Humans spread the disease through the movement of infected nursery stock and possibly with firewood and soil on the bottoms of shoes and boots. (Although viable spores have been detected on boots there is no evidence that the pathogen is spread this way.)

No pesticide to control sudden oak death

There is no pesticide registered by the U.S. Environmental Protection Agency that will eradicate the organism that causes sudden oak death. The only way to stop the disease is to cut down and burn infected plants or trees.

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