Epidemiology of Phytophthora ramorum in Oregon tanoak forests

Abstract

We followed the local intensification and dispersal of Phytophthora ramorum Werres, De Cock, & Man In’t Veld in Oregon tanoak ( Lithocarpus densiflorus (Hook & Arn.) Rehd.) forests from its initial detection in 2001 through 2006, coincident with a continuing eradication effort. The initial infested area included nine scattered sites below 400 m elevation, close to the Pacific Ocean near Brookings, Oregon. In subsequent years, one-half of new infections were within 122 m of a previous infection, and 79% of the newly detected trees occurred within 300 m of a previously identified tree. Dispersal up to 4 km was occasionally recorded. Initial infection occurred in the upper crowns of tanoak trees. The pathogen was recovered in rainwater collected beneath diseased tanoak trees in every month from November 2006 through October 2007. Twenty-four multilocus microsatellite genotypes were identified among 272 P. ramorum isolates collected from Curry County. Genotypic analysis provided independent estimates of time of origin of the Oregon infestation, its clustered distribution, and dispersal distances. In all sampling years, 60%–71% of the isolates belonged to the same multilocus genotype. In 2001, 12 genotypes were detected and new genotypes were identified in each of the subsequent years, but all isolates belonged to the same clonal lineage. Knowledge of local intensification of the disease and long-distance dispersal should inform both Oregon eradication efforts and national quarantine regulations.

Modeling when, where, and how to manage a forest epidemic, motivated by sudden oak death in California

“…The only treatment shown to be effective in reducing pathogen prevalence at the landscape scale is removal of host species (22), as has been practiced in the United Kingdom for a number of years (21). In North America, however, large-scale management has not been attempted.…”

“…Nevertheless, an outbreak of SOD in Curry County, Oregon, has remained relatively small in comparison with CA due to active management by host removal since first detection in 2001 (23). The attempted eradication of PR in Oregon in the very earliest stage of that outbreak was only possible because the potential impacts were already clear from CA, and because its epidemiology was beginning to be characterized (22). We consider 2002 to be the earliest that statewide attempts to prevent further spread of PR in CA could, in principle, have been attempted.…”

Effects of Host Variability on the Spread of Invasive Forest Diseases

“…For example, the oomycete plant pathogen Phytophthora ramorum (Werres, De Cock & Man in't Veld), has a broad host range affecting both natural (forests) and semi-natural (urban green area) environments and hardy nursery stock. In western USA, P. ramorum has largely influenced the California oak woodlands landscape through diffuse impacts on a large number of host species [10,11], causing lethal stem infections on 'canker hosts' (mainly Notholithocarpus densiflorus (Hook. & Arn.)…”

Evolution of an Invasive Species Research Program and Implications for Large-Scale Management of a Non-native, Invasive Plant Pathogen

“…The P. ramorum world is characterized by good coordination and communication between the various segments of the land management and research communities, as well as good outreach to the public and resource managers. There have been attempts to manage through regulation (HRI P. ramorum Industry Working Group, 2008;COMTF, 2008a), and regional-scale eradication attempts are ongoing in Oregon and the UK (Goheen et al, 2004;Kanaskieet al, 2009aKanaskieet al, , 2009bHansen et al, 2008;Forestry Commission Great Britain, 2011). In California, the pathogen became established in wildlands faster than eradication attempts could be mounted, but we have observed numerous small-scale neighborhood or single-property management attempts at the wildland-urban interface (Alexander & Lee, 2010) as well as ongoing management experiments that are slowly establishing the efficacy of individual management techniques at a larger scale (Valachovic et al, 2008;Garbelotto & Schmidt, 2009;Swiecki& Bernhardt, 2009).…”