Impact of Eradication Programs on the Temporal and Spatial Dynamics of Plum pox virus on Prunus spp. in Pennsylvania and Ontario, Canada

The goals of this research were to quantify the impacts of the Pennsylvania and Ontario Plum pox virus (PPV) eradication programs on the spatial and temporal dynamics of PPV epidemics on Prunus spp. The incidence of PPV-positive trees detected over time decreased in both Pennsylvania (-ln 0.85 units per year) and Ontario (-ln 0.51 units per year); however, PPV incidence per year decreased only 60% as fast in Ontario as in Pennsylvania. Marked point pattern analysis revealed that PPV-positive Prunus blocks in Pennsylvania were clustered for distances of 0.7 to 4.3 km, whereas PPV-positive blocks in Ontario were clustered for distances of 1.0 to 25.0 km. Multiyear spatiotemporal analyses revealed that the locations of PPV-positive blocks detected were spatially dependent upon the locations of PPV-positive blocks detected during the previous year. In Pennsylvania, between 2002 and 2006, distances to 95% of newly detected PPV-positive blocks occurred within 10 and 20 km from the previous year's PPV-positive blocks. In Ontario, 95% of new PPV-positive blocks occurred within 500 to 900 m from PPV-positive blocks detected the previous year. Until 2011, the PPV eradication policy for Prunus blocks in Ontario was triggered by a threshold incidence or PPV-positive tests for three consecutive years. Although the Ontario program was highly successful in reducing PPV incidence from 2001 to 2008, PPV was not eradicated. This study provides important quantitative information concerning the impact of PPV eradication programs on the spatial and temporal dynamics of PPV epidemics in Pennsylvania and Ontario. The analyses employed in this study may help to improve the effectiveness of present and future PPV eradication programs.