Aphanomyces Root Rot (ARR) is a disease caused by the oomycete pathogen, Aphanomyces euteiches. A. euteiches can infect many legume species, one of which is alfalfa (Medicago sativa). Aphanomyces is often seen in disease complex with other root rotting diseases, such as Phytophthora and Pythium Root Rot. Fieldwide symptoms of Aphanomyces infection include thin, stunted growth above soil with yellowing leaves and rotting root systems below the soil surface. ARR is an economically important disease because it affects alfalfa at both the seedling and mature plant stages causing severe yield loss.