This study examines the effects of climatic conditions on interactions among pea and lentil yields, pea aphid Acyrthosiphon pisum (Harris) infestations, and outbreaks of PEMV (Pea enation mosaic) and BLRV (Bean leaf roll) viruses in the Palouse region of easternWashington. The study analytically and empirically evaluates the effects of aphid outbreaks on per acre yields, implicitly including the effects of adopted pest management activities and explicitly taking into account possible effects of climatic conditions on the severity of pea aphid outbreaks. The results show that aphid outbreaks have historically decreased pea and lentil yields by approximately 5% and 7% on average respectively.