Watch for sudden oak death

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We need to be aware of a serious plant disease problem. It is called sudden oak death (SOD), Phytophthora rumorum, infesting plants in California, Oregon, Washington state and British Columbia. In 2002, the USDA enacted a federal quarantine (7 CFR 301.92 Ð 11) to limit the spread of the disease from areas of known infestation. The quarantine includes the 12 California counties and Curry County, Ore.

This disease affects certain trees, shrubs, and many other plants, causing fatal bark lesions in several species of oaks. It also causes leaf blights on many other species of trees, shrubs, and other plants. Lilacs, viburnums, Wood's rose, rhododendron, and pieris are some of the many plants affected. Horse chestnuts and European beech also can be infected. SOD has killed thousands of red oak and tan oak found in California and Oregon and is known to infest a wide variety of native and ornamental plants. A list of known host plants and associated host plants is available at, or by contacting Peggy McKie, nursery and landscape program manager, Nevada Department of Agriculture, 688-1182, ext. 243.

The symptoms of SOD are not well known on many of the host plants. Photographs of symptoms of the disease on selected host plants can been seen on the Washington State Department of Agriculture's Web site,

It is unclear how SOD spreads. Evidence suggests that infested plants moved interstate would serve as a pathway for introduction of SOD to other areas of the United States. It is most likely to develop in certain climate zones and under certain weather conditions.

You are encouraged to contact Shouhua Wang, Ph.D., state plant pathologist, Nevada Department of Agriculture, 688-1182, ext. 246, or, if you notice what you believe to be symptoms of SOD on any of the host or associated host plants shown below. You may bring samples to the department's office in Reno. Call for directions.

If steps are not taken to stop the spread of SOD, it is expected that the disease will eventually spread to all areas in the United States with host plants and favorable environmental conditions. Because SOD is fatal to many species of oaks, this would have potentially devastating results for our forests and natural areas, and for the nursery and lumber industries. It would also negatively affect the ability of U.S. companies to ship plants and wood products overseas.

Although it is not known if SOD can become established in Nevada, the disease is of concern because of its potential to infest established plantings in homes, commercial plantings and parks. In addition, there are plants native to Nevada, such as oaks and manzanita, related to the regulated hosts of SOD and could be infested by infected nursery stock planted in landscapes, revegetation projects or parks. This is particularly true of the areas around Lake Tahoe, the east side of the Carson Range in western Nevada, and throughout the state where native host plants are exposed to introduced plants infested with SOD.

For information about SOD, call the U.S. Department of Agriculture's "Sudden Oak Death" hotline, (888) 703-4457. The following Web sites also are available.


- www.aphis.usda/gov/ppq/ispm/sod



For information on other gardening topics, call 887-2252, 782-9960, or your local University of Nevada Cooperative Extension office. Check out many useful horticulture publications at "Ask a Master Gardener" by e-mailing

JoAnne Skelly is the Carson City/Storey County Extension Educator for University of Nevada Cooperative Extension. E-mail her at


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