Distribution of Phoma sclerotioides and incidence of brown root rot of alfalfa in Wyoming, U.S.A.

Brown root rot of alfalfa, caused by Phoma sclerotioides, has been reported from Alberta and Saskatchewan, Canada, and was the cause of widespread “winterkill” of alfalfa in southwestern Wyoming, U.S.A., in 1996. Affected plants exhibit characteristic dark, sunken, necrotic lesions on upper tap and lateral roots. Surveys of irrigated fields were conducted in nine counties to determine distribution of the pathogen within Wyoming. Symptomatic as well as asymptomatic root-tissue isolations demonstrated that P. sclerotioides was present in most counties surveyed, indicating its distribution may be statewide. Disease incidence was assessed in two fields where P. sclerotioides occurred. Results indicate that the pathogen is uniformly distributed within infested fields.