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Disease Note.

Botrytis cinerea Blossom Blight of Alfalfa on the Canadian Prairies. B. D. Gossen, Agriculture and Agri-Food Canada Research Centre, Saska- toon, SK, S7N 0X2. S. R. Smith, Plant Science Department, University of Manitoba, Winnipeg, MB, R3T 2N2; and R. G. Platford, Department of Agriculture, Winnipeg, MB, R3T 2N2. Plant Dis. 78:1218. Accepted for publication 13 July 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1218D.

In late July 1993, a blossom blight was widespread and severe in alfalfa (Medicago sativa L.) seed production fields in central Manitoba and occurred sporadically in Saskatchewan and Alberta. The cultivar Vernal was particularly susceptible. Botrytis cinerea Pers.:Fr. was isolated from infected flowers, and pathogenicity was confirmed in a greenhouse test. Infected flowers were quickly covered by gray mycelium with abundant sporulation. Visible discoloration extended into the petioles but not into the stem. Leaflets became infected only after senescence. Plants with severe symptoms produced little or no seed. Cool, wet weather appears to be a necessary precondition for epidemic increase of blossom blight (1,2). These conditions occurred throughout the region at flowering; e.g., at Brandon, Manitoba, rainfall totaled 237 mm in July and August, which was 68% above the 30-yr mean. Blossom blight of alfalfa has not been reported previously from western Canada, although B. cinerea is isolated routinely from other hosts.

References: (1) E. W. Hanson. Plant Dis. Rep. 37:467, 1953. (2) F. R. Jones. Plant Dis. Rep. 36:61, 1952.