Phytophthora ramorum, the funguslike micro-organism that causes the plant disease Ramorum blight on landscape ornamentals and Sudden Oak Death on tanoaks and susceptible species of oak on the West Coast, has been confirmed in the garden section of a hardware store in Portage, according to state entomologist Bob Waltz.
The infected sample was found two weeks ago from a species of Viburnum (a common shrub) that was shipped to the store from an Oregon-based supplier.
Information on the shipment was provided by the U.S. Department of Agriculture Animal and Plant Health Inspection Service, Plant Protection Quarantine (USDA APHIS PPQ). Samples taken from the plants by DNR inspectors were first screened for the presence of Phytophthora species by the Purdue Plant and Pest Diagnostic Lab, then forwarded to the USDA APHIS PPQ laboratory in Beltsville, Md., where P. ramorum was confirmed.
Waltz, who praised the cooperation of the store owner, said early detection is a key toward stopping the spread of this pathogen. Because P. ramorum is a regulated organism, destruction and disposal protocols are coordinated by state regulatory officials. The plants have been removed from the site and buried deep in a landfill, per USDA APHIS PPQ protocols.
Janna Beckerman, Purdue University extension plant pathologist, said that this is the first but probably not the last Indiana occurrence of this funguslike micro-organism.
"The introduction of P. ramorum is a cause for concern, not alarm," Beckerman said. "Despite our best regulatory efforts, this pathogen has been, and could again be introduced into Indiana via nursery stock.
"The host range of this pathogen infects more than just oaks, and the host range includes many of our native plants, and landscape plants. Our goal is to keep this disease from becoming established in our Indiana landscapes and forests, and the best way to achieve this goal is to educate the public about this disease."
A similar finding at an Indianapolis greenhouse last week proved negative for P. ramorum at the USDA APHIS PPQ laboratory.
Waltz said P. ramorum spreads in the West Coast areas where it is established in the natural landscape through infected plant material, rainwater and soil. The pathogen thrives in cool, moist weather. Waltz said that Indiana has been rated as being at moderate risk for this disease by the U.S. Forest Service. Most of the state's at-risk sites are in the southern region, where oak forests and elevated topographies could potentially support the disease.
Waltz said that P. ramorum does not currently occur naturally in Indiana. The pathogen's only pathway into the state is through infected plant material that is transported over the state line. Because of this, the DNR has been actively surveying for P. ramorum in Indiana through several different survey targets and by work with other agencies.
Jack Seifert, state forester, said that the movement of such diseases across state and country boundaries is going to become more common.
"This is an issue we are going to have to deal with in society as products move about," he said. "It's just part of worldwide commerce."
Targeted surveys of plant material shipped into state nurseries and nursery dealers are conducted by the DNR Division of Entomology and Plant Pathology as an annual survey with the USDA APHIS PPQ and the Purdue University Plant and Pest Diagnostic Laboratory. The DNR Division of Forestry actively surveys woodlands for P. ramorum through soil surveys it coordinates with the U.S. Forest Service and with DNR's Entomology & Plant Pathology division.
The data being recorded from these surveys are used to develop an inventory of the Phytophthora species found in Indiana and other participating states. This national study is leading to better identification of native species that might in some cases be confused with P. ramorum and helping to make certain that P. ramorum is not already established.
P. ramorum was first identified in 1993 in Germany and The Netherlands, but its geographical origin is unknown. Since its discovery in North America in 1995 in central coastal California, the pathogen has caused widespread dieback of tanoak and several oak species in the central and northern coastal counties of the state. The pathogen has also been found in nurseries in California, Oregon, Washington state and Canada's British Columbia.
Natural occurrences of P. ramorum in the United States are found only along the West Coast, but widely traded rhododendron, lilac, Viburnum and other ornamental plants can be infected. This fact, combined with the demonstrated susceptibility of some important Eastern oaks, makes introduction into those forests a significant risk.
Due to P. ramorum's broad host range and non-descript symptoms, trees and shrubs infected with the pathogen are difficult to distinguish from those with other diseases. In trees, P. ramorum causes large, bleeding cankers on the trunk or main stem, accompanied by the wilting and browning of leaves. Tree death may occur within several months to several years after initial infection. Infected trees may be infested with ambrosia beetles, bark beetles and sapwood rotting fungus.
Symptoms of leaf infection vary with host, but often consist of dark gray-to-brown lesions with indistinct edges. These symptoms can readily be confused with those of other diseases.
The Purdue University Plant and Pest Diagnostic Laboratory maintains a Web site (www.ppdl.purdue.edu/PPDL/SOD.html) that includes a checklist to assist growers and homeowners in determining if they have a sample that should be submitted for further evaluation. The Indiana Nursery and Landscape Association (www.inla1.org/) also has been active in keeping its membership informed about P. ramorum.