Mapping disease in the Palouse pea aphid (Acyrthosiphon pisum (Harris)) pathosystem

In the Palouse region of the Inland Pacific Northwest two plant viruses have the potential to be significant constraints on cool season food legume (CSFL) production. The pea aphid Acyrthosiphon pisum (Harris) is the primary vector of the viruses: Pea enation mosaic virus (PEMV) and Bean leaf roll virus (BLRV). The spread and distribution of the two viruses is annually variable and unpredictable. The study of any disease requires the quantification of a salient outcome in an exposed population over time. Every CSFL field in the study region has a probability (background risk) of containing infected plants. This project is interested in using disease surveillance data to estimate that probability, as well as estimating the expected epidemic expansion rate subsequent to primary infection. A plant epidemic is the product of dispersal processes occurring within a heterogeneous landscape. At field scale, risk of infection for a randomly chosen plant may be higher than the background risk as a function of a field’s location within the larger landscape matrix. From 2007 to the present field surveys of CSFL fields in the Palouse study region have been conducted annually to monitor for the presence of PEMV/BLRV. These data are georeferenced and can be used to generate a map of disease prevalence on the landscape through time. These data are also being used to address the above question: is risk variable, and is spatial location an excess risk factor?