Reviewed and Additions Provided by:
Dr. Pierluigi (Enrico) Bonello
Dr. Francesca Peduto Hand
The Ohio State University, Department of Plant Pathology
The Ohio Department of Agriculture (ODA) has announced in an official press release a confirmed interception of the plant disease-causing pathogen Phytophthora ramorum in Ohio. You can access the press release by clicking on the hotlink at the end of this Alert.
P. ramorum is a water mold organism that causes ramorum blight on over 100 host plants, including rhododendron and lilac, and sudden oak death (SOD) in coastal areas of California and Oregon. SOD has proven to be deadly in California and the Pacific Northwest on oaks (Quercus) and tanoaks (Notholithocarpus). On other hosts, this pathogen causes leaf spots and branch dieback.
A shipment of infected plants, including numerous rhododendron types and lilac, from a nursery in the Pacific Northwest, was sent to a nursery in Oklahoma and subsequently shipped to Walmart and Rural King locations in a number of eastern U.S. states, including Ohio. Though this pathogen was found on rhododendrons and lilacs intercepted here, there was no shipment of oaks with SOD.
For context, it is important to remember the Plant Disease Triangle: a susceptible host, a virulent pathogen, and an environment conducive to disease are all necessary for a particular disease to occur. Over the almost 25 years in which SOD and ramorum blight have been regulated disease issues, we do not know of any cases of this disease becoming established in the U.S. other than those coastal areas of California and the Pacific Northwest.
Although it is impossible to completely know for certain the potential risk of this pathogen becoming established here, Ohio is not considered to be a particularly likely candidate for establishment of SOD. P. ramorum has never been detected before in Ohio nurseries, landscapes, or forests. That said, the vigilance of ODA and our plant regulatory system should be lauded relative to this interception.
Let us proceed with caution. If your customers have rhododendrons or lilacs purchased at Walmart or Rural King between March and May of this year and you suspect they may be infected, drawing from the ODA Press Release, "Plants can be destroyed by burning, deep burial or double-bagging the plant, including the root ball, in heavy duty trash bags for disposal into a sanitary landfill (where allowable). Consumers should not compost or dispose of the plant material in municipal yard waste."
In addition, it is important to keep in mind there are many different diseases, insects, and physiological problems that may occur on rhododendrons, lilacs, and oak. To sharpen your plant problem diagnostic skills, we will make a point of reviewing some of these at diagnostic training events yet to come this summer and fall. These include a workshop that will be held on the OSU-Mansfield Campus on August 2 and the Ohio Plant Diagnostic Workshop on the OSU-Wooster Campus on September 6 as well as the Greater Cincinnati Diagnostic Walk-Abouts on August 5, September 9, and October 14.
You can access the ODA Press Release by clicking this hotlink: