Michigan - An Uninfested State Responding to the Threat of Phytophthora ramorum, Causal Agent of Sudden Oak Death
Andrew J. Storer1, Gerard C. Adams2, John Hill3, Frank J. Sapio4, and Robert Heyd5
The pathogen that causes Sudden Oak Death, Phytophthora ramorum, is not known to occur in the state of Michigan. This pathogen causes a canker disease on oaks and tanoaks and other diseases on host plants in other plant families. The current knowledge base about this pathogen suggests that the risk of introduction into Michigan is through the movement of diseased or otherwise contaminated nursery stock. Other risks for entry include recreational activities that involve the transport of fire wood or contaminated soil. The potential impact in Michigan is great due to the presence of known susceptible hosts, including red oak (Quercus rubra), and climatic conditions that have not yet been demonstrated to limit the survival of the pathogen. This impact will be increased if other susceptible hosts are identified from the native plants of Michigan, especially understory plants that may serve as reservoirs of inoculum in forest environments.
Given the potential impact of this pathogen, all available measures should be taken to preclude the possibility of this pathogen being introduced into Michigan. The current federal regulation does not completely protect Michigan from contaminated material from States not listed as infested by this pathogen, and the screening methods for shipments of plants may be inadequate. In addition, early detection of the pathogen in Michigan will be essential to any plan for eradication. Towards this end an initial survey of nurseries carrying rhododendron stock has been completed. In this survey, rhododendron leaves with leaf spots were collected from nurseries around the state and screened for the presence of P. ramorum. Screening techniques included isolation onto PARP medium and the use of molecular diagnostic tools developed in California. While nationwide detection efforts include a focus on evergreen understory species, deciduous hosts are also known to harbor the pathogen in the understory in infested areas.
Specific information needs for Michigan include:
- Environmental constraints on the establishment and development of the pathogen
- Susceptibility of shrubby plants associated with Michigan hardwood forests
- Further information on the biology and epidemiology of P. ramorum
- Amount and location of host material imported from California and other states
- Optimal survey protocols for nurseries and the field that include timing of survey, evaluation of observed and reported oak and other host mortality, training resource managers in Sudden Oak Death identification and sampling procedures, and an effective reporting system
- Planned responses to detection of the pathogen
1School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI 49931; (906) 487-3470; storer@mtu.edu
2Department of Plant Pathology, Michigan State University, East Lansing, MI 48824
3Pesticide and Plant Pest Management Division, Michigan Department of Agriculture, Lansing, MI 48909
4Forest Heath, Inventory, Monitoring and GIS, Michigan Department of Natural Resources, Lansing, MI 48909
5Forest Health and Health Monitoring, Michigan Department of Natural Resources, Marquette, MI 49855
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