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What Is Sudden Oak Death?

October 30, 2002

Sudden oak death (SOD) is a fungal disease that causes a rapid decline and death of oaks. The name is a bit misleading because it also occurs on other tree and shrub species, 17 in all. Symptoms vary from leaf spots to twig blight to trunk cankers. Roots do not show symptoms.

The causal fungus of SOD is Phytophthora ramorum. At present, the disease has been identified only in ten California counties and one Oregon county. Oaks affected are tan oak, coast live oak, and California black oak, none of which grows in Illinois. Research has shown that red and pin oaks are susceptible when artificially inoculated. In addition, some other plants grown in Illinois can serve as hosts, including rhododendron, azalea, and Douglas-fir. Obviously, there is great concern that the disease might move on these plants to other areas of the country.

SOD causes rapid decline of oaks, usually resulting in death in 1 to 3 years. On oak, the disease causes a bleeding canker on the stems or trunk. These cankers ooze a black or reddish fluid. The wood under them has black zone lines evident when bark is removed. Once crown dieback begins, the leaves turn brown in a few weeks.

Because of the concern of movement of this disease out of California and Oregon, USDA began regulating the shipment of all host plants in February of 2002. The animal and plant health inspection service (APHIS) has surveys planned for some of the southeastern states (GA, SC, NC, TN, and VA) where the disease is most likely to take hold. These surveys are slated for the spring of 2003. Oklahoma plant pathologists have already initiated some nursery surveys and have not yet found the disease.

There is a tremendous amount of information available on this disease on the Internet. A good source to start with is the USDA "Sudden Oak Death Pest Alert," NA-PR-02-02, at http://www.na.fs.fed.us/spfo/pubs/pest_al/sodeast/sodeast.htm.

Author: Nancy Pataky


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