Regulatory considerations in assessing the potential for Phytophthora ramorum to cause environmental impact to ecozones outside the west coast "fog belt" in North America

Sudden oak death (SOD) is a disease caused by Phytophthora ramorum that is characterized by lethal trunk lesions that affect tanoak (Lithocarpus densiflorus), and a few oak species, principally coast live oak (Quercus agrifolia). It was first observed in Marin County, California, in 1994, and now has been reported to have caused extensive tree mortality in the West Coast “fog belt” area that generally extends less than 30 km inland, from Monterey County, California, in the south, to Curry County, Oregon, in the north. While the plant communities vary somewhat, it is notable that the zone closely mirrors the distribution of the coast redwood (Sequoia sempervirens). Tanoak and California bay laurel (Umbellularia californica) are present throughout the zone. In California, infected bay laurel produce abundant P. ramorum sporangia which facilitate the spread of the pathogen, but in Oregon pathogen spread is primarily attributed to inoculum produced on tanoak foliage. Climate-host models generated to assist in early detection, survey, mitigation, and formulation of regulatory policy, have generally indicated that the west coast and the eastern conterminous United States (U.S.), especially the Appalachian Mountains, are at similar risk for infection. This risk area also extends up into coastal British Columbia, Canada. Indeed, regulatory surveillance and certification programs to detect P. ramorum on nursery plants moving in inter-state trade, both in the U.S. and Canada, have resulted in detections in many of these areas since 2002, suggesting the ability of the pathogen to survive and move within the nursery environment. However, no P. ramorum forest or wildland areas has been reported outside the current ecozone in California and Oregon, despite large shipments of host plants from known infested areas. Possible reasons for this, with consideration of when and how P. ramorum may have been introduced to North America, what is achievable through nursery certification, and the epidemiological uniqueness of the P. ramorum ecozone in the West Coast “fog belt”, are discussed from a regulatory perspective.