Occurrence of Verticillium wilt of alfalfa in southern Alberta, 1980-86.

Surveys from 1980~86 revealed that verticillium wilt, caused by Verticillium albo-atrum, was a widespread and often serious disease of alfalfa in southern Alberta. It was found in 156 (10.1%) of 1537 fields surveyed during this period. The disease occurred most frequently in irrigated alfalfa fields used for hay, pasture and dehydrated products.!t was rarely observed in seed and dryland fields. The highest incidence and severity of wilt were seen in the Lethbridge-Taber area. The disease was more extensive and destructive in stands four years of age and older. Although it was positively diagnosed for the first time in Alberta in 1980, alfalfa seed assay data suggest that the disease was present in southern Alberta prior to this date. Many producers plowed down wilt-infected alfalfa crops because of stand debilitation and to minimize the risk of disease spread to nearby fields.