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What Is Ramorum Blight and Why Should We Be Concerned?

April 4, 2006
You may have heard of this disease as SOD, sudden oak death, ramorum leaf blight, or ramorum dieback. The fungal-like pathogen, Phytophthora ramorum, was confirmed on oaks on the west coast of the United States in 1995 and has since been detected in 22 states. Originally named sudden oak death because it ultimately moved to oaks and caused them to die, the disease has since been shown to infect 100 hosts (and that number keeps increasing), including shrubs and trees. Because turf growers don't wish to cause a scare in the turf industry and turf is not involved, the SOD moniker has been dropped and the more appropriate name of ramorum blight has been assigned.

The new USDA APHIS Web site about Phytophthora ramorum programs can be found at http://www.aphis.usda.gov/ppq/ispm/pramorum. In March 2004, it was determined that the disease had been shipped out of California, possibly to many U.S. nurseries. APHIS issued an emergency Federal Order (http://www.aphis.usda.gov/ppq/ispm/pramorum/pdf_files/federalorder12-21-04-final.pdf) that bolstered the agency's initial P. ramorum restrictions by regulating the interstate movement of plants for planting, including houseplants and propagative materials, from all commercial nurseries in California, Oregon, and Washington. The Federal Order, which became effective on January 10, 2005, was enacted in response to detections of P. ramorum at commercial nurseries in California, Oregon, and Washington that were outside quarantined areas.

Many states, including Illinois, have conducted nursery surveys the last 2 years to monitor plants received from the West Coast. The University of Illinois Plant Clinic has been the testing agency for samples collected by the Illinois Department of Agriculture and Illinois APHIS inspectors. Phytophthora ramorum has not been found in Illinois. The nursery survey will continue in 2006.

The APHIS list of hosts and associated hosts of this pathogen contains 100 plants. You can view the list (updated frequently) at http://www.aphis.usda.gov/ppq/ispm/pramorum/pdf_files/usdaprlist.pdf. Not all of these hosts will grow in Illinois, but many do. Some plants of concern include rhododendron, honeysuckle, viburnum, camellia, pieris, vaccinium, Douglas-fir, white fir, horse chestnut, and others.

The pathogen forms spores on blighted tissues of leaves and stems of infected shrubs. These plants may be shipped to nurseries, purchased by landscapers, and planted near established trees. Ultimately, the main concern is that the oak forests will be threatened. The disease has killed thousands of oaks in California.
This disease can cause symptoms that range from oozing cankers (on trees) to leaf blights, so it can be difficult to diagnose or to distinguish from other problems. Pictures and symptom descriptions can be found on the Phytophthora ramorum fact sheet produced by the North Central Region Pest Management Center and viewed at http://www.ncpmc.org/alerts/suddenoakdeath/index.cfm. There are other helpful links to information on this disease at that site.

Keep an eye on camellia, rhododendron, viburnum, pieris, kalmia, or lilacs planted in the last 3 years and obtained from the West Coast. If these plants develop extensive cankers, blights, or dieback, review the information above. The University of Illinois Phytophthora ramorum Web site, http://pramorum.cropsci.uiuc.edu/index.cfm?id+screen, addresses common questions about this disease and lists screening questions for determining the need to submit a plant sample for Phytophthora ramorum testing. Watch for more updates about this disease as the season progresses.

Author: Nancy Pataky


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