The cool season legumes are susceptible to several virus diseases. The most serious in the region are Pea enation mosaic virus (PEMV) and Bean leaf roll virus (BLRV) both of which are vectored virtually exclusively by the pea aphid, Acyrthosiphon pisum (Harris) (Klein et al. 1991, Clement 2006, Clement and Eigenbrode, 2007). Aphid outbreaks and virus disease epidemics occur intermittently and unpredictably in pea and lentil in the region threatening the viability of the industry. The most recent epidemic occurred in 2005. Although occurring in 6- to 9-year intervals their cause is unknown. Virus prevalence among years in the Palouse is greater during aphid outbreaks but not consistently so. In non-outbreak years, severe injury from virus disease can still occur in individual fields. Current practice for aphid control and virus reduction is to treat aphids aggressively with dimethoate when virus risk is considered high. Growers currently have no quantitative way to assess this risk, however, and rely on inspection of plants for symptoms and their own perceptions of risk. Other growers, seeking to reduce inputs try to avoid treating for aphids, leaving the crop open to virus injury. When virus is not suspected, insecticides are often used to prevent direct injury by pea aphids and simultaneously to treat for pea weevil (Bruchus pisorum). Insecticide-use decisions currently depend on simple rules-of-thumb (Homan et al. 1992), based on opinion rather than quantitative guidelines. These recommendations do not provide producers with loss models or economic thresholds that account for crop value, insecticide costs and crop yield potential. Critically absent are economically justified recommendations taking into account the effects of pea aphid as a vector of viruses. The primary purpose of this project is to provide necessary economic information for formulation and implementation of coordinated, virus-forecast based, pea aphid control strategies with the goal of reducing the industry?s vulnerability towards PEMV and BLRV. The key for such management strategy is that if producers knew in advance when severe epidemics of PEMV and BLRV were likely to occur, and whether their particular fields were prone to infection, they would be forewarned of the need to apply recommended vector control measures to manage these viruses. Alternatively, if risks were known to be low, growers could manage the aphids as direct pests, reducing pesticide use and concomitant environmental and economic impacts. However, it is important that such forecast based conditional management strategy be economically justified. The model will be based on profit maximization framework and will produce optimal, cost minimizing, strategies for PEMV and BLRV virus control. The model will be used to provide answers to what is the economic value of virus forecast based strategies for controlling pea aphids as virus vectors. The model will also permit economic analysis of the value of information, risk management, economic interrelationships in production input usage, pest dynamics, etc. (McCarl, 1981).