Of 12 onion seed lots harvested in the semi-arid Columbia Basin of Washington in 1999 or 2000, 8 were infected and 10 infested with Botrytis aclada at incidences of 1 to 10% and 2 to 26%, respectively. Twenty to forty plants were sampled from each of nine direct-seeded, biennial seed crops in April, June, and July 2001 and assayed for Botrytis spp. Six direct-seeded crops were sampled in October and November 2001 and April, June, and July 2002. One bulb-to-seed crop was sampled in April, June, and July 2002. The incidence of B. aclada increased through each season, reaching 100% in most fields by July. Infections were primarily asymptomatic, with no apparent relationship between plant infection and infection of harvested seed. B, cinerea, B. squamosa, and B. porri were detected in 16, 4, and 4% of the fields, respectively, at lower incidences than B. aclada. Harvested seed from 15 of the fields were infected with B. aclada at <1 to 28%. B, cinerea, B. porri, and B. squamosa were detected in three, three, and none of the harvested lots, respectively.