Nematode angular leaf spot of dry bean in Wyoming.

A new foliar disease of dry bean, nematode angular leaf spot (NALS), is caused by Aphelenchoides ritzemabosi. The disease is typified by numerous dark, angular lesions on leaves and occasionally a superficial necrosis on the upper surface of the petiole. Diagnosis of NALS is based on the presence of foliar symptoms and recovery of nematodes from symptomatic tissue. Infested fields were infrequent in a field survey of 7,175 ha in Wyoming conducted during a 3-year period. The field survey represented 17% of the crop harvested during those years. Therefore, it is unlikely that NALS will cause economic yield loss unless conditions for nematode survival and foliar parasitism are unusually favorable. The nematode is also known to parasitize alfalfa foliage in Wyoming and other western states. Infested dry bean fields found during the survey had a recent history of alfalfa production. Therefore, alfalfa and dry bean crop rotation provides a potential mechanism for nematode survival. Parasitic nematodes persisted in air-dried bean leaf tissue for at least 27 months, which suggests that persistence of NALS inoculum in crop debris is likely to occur in the field.