Sudden oak death (SOD) is a disease that has the ability to infect a wide range of hosts. It is not limited to oak as the name would seem to imply. SOD is caused by a fungal-like pathogen, Phytophthora ramorum, and was first found in the United States in California in 1995. Initially, the disease was present only on California plants (such as tanoak) that could not survive in Illinois. Presently, 28 plant species have been proven as hosts. Another 36 plants have been associated with this fungus. The fungus has been proven to be present on those 36 hosts, but Koch’s postulates have not yet been completed to prove these are true hosts. All 64 species are under regulatory scrutiny. Some of those species that can be grown outdoors in Illinois include witch hazel, Douglas-fir, Japanese pieris, rhododendrons, viburnums, and lilacs. Check out the host list at http://www.aphis.usda.gov/ppq/ispm/sod/usdasodlist.html, an official APHIS Web site.
Why are we so concerned about this disease? SOD has the ability to kill tanoaks in California. It has been shown to be transmitted in greenhouse situations to red oaks although natural infection has not been proven as yet. SOD has the potential, therefore, to cause considerable damage to eastern oak forests. In addition, many other plants can host this fungus. Those hosts may not be killed by the fungus but could serve as hosts on which the fungus could form spores that spread to other plants. Finally, this disease has now been confirmed in 21 states.
What is being done in Illinois to address this problem? In March 2004, when it was discovered that plants had been shipped from some California SODinfected nurseries to other U.S. states, paperwork was initiated to trace those shipments. APHIS and Department of Agriculture inspectors then inspected all recipient nurseries, and suspect plants were sampled and tested for the presence of Phytophthora. In Illinois, those tests were run at the University of Illinois Plant Clinic. All samples from the trace-back inspections in Illinois were negative. The disease was not found. Currently, a national nursery survey is under way by APHIS and state departments of agriculture. Nurseries are inspected for SOD symptoms, especially on plants shipped from the West Coast. In Illinois, suspect plants are being tested by the Plant Clinic, using ELISA assays specific to only the Phytophthora genus. According to national APHIS protocol, the specific fungus, Phytophthora ramorum, can be confirmed only by using PCR diagnostic testing. If a positive Phytophthora result is obtained by ELISA, the sample is then sent to national testing labs in Beltsville, Maryland. PCR tests for Phytophthora ramorum are performed on the suspect samples from each state. Thus far in Illinois, 146 nursery samples have been sampled and tested for Phytophthora using ELISA assays. No positive Phytophthora ramorum samples have been found.
What sort of educational opportunities exist in Illinois concerning SOD? An Illinois SOD task force has been established and is planning some educational opportunities this winter. National training will be conducted for Extension specialists and educators, regulatory personnel, state foresters, and a few others. After this meeting, the task force will meet to finalize an Illinois detection and response plan for sudden oak death. Training for arborists, landscapers, nurserymen, and Master Gardeners will occur in March. Information about this opportunity will be released as it is available.
Consult the North Central IPM Center’s Web site at http://www.ncpmc.org/sod/ for examples of existing state Phythophthora ramorum detection plans for homeowner plants, as well as some helpful Web resources. Additional information and references are available in a “Sudden Oak Death Alert” article in issue no. 1 of this newsletter.