Epidemiology of Plum pox ‘D’ strain in Canada and the USA

Abstract

The successful 10-year eradication programme for Plum pox virus (PPV) in Pennsylvania, USA was based on vigilant surveys followed by removal of all Prunus spp. within 500 m of confirmed PPV-positive trees, resulting in declaration of eradication in October 2009. In comparison, in Ontario, Canada, when PPV was first discovered in 2000, the low incidence but widely dispersed epidemic extended throughout the stone fruit industry. The Canadian programme was initially predicated on vigilant surveys plus PPV-infected tree and block removal to reduce PPV incidence, followed by increasingly stringent eradication protocols over time. However, eradication was not achieved prior to programme termination in 2011. Retrospective analyses of the Canadian epidemic indicated that the estimated PPV distribution from known sources followed a pulse-peak-decay function. The function indicated that viruliferous aphids transmitted infections most commonly at 43 m (peak) distance from prior infections, but PPV distribution also has a long (decaying) tail. A Weibull model, fitted to the proportion of new PPV-infected trees detected, demonstrated that 95% of new infections occurred within 628 m, 465 m and 317 m distances, for 1, 2 and 3-yr moving averages, respectively. Results suggest that eradication might be achievable by employing a 317–628 m cull radius distance. The discontinuation of the PPV eradication programme in Ontario will result in an increase of PPV in the region, if no spread prevention measures are implemented, and threaten the nearby New York State stone fruit industry. A risk-based survey methodology for commercial and residential stone fruits has been developed to sample Prunus orchards throughout New York that emphasizes proximity to prior PPV discoveries, and proximity to the Canadian border.