Burning to reduce sclerotia of Sclerotinia sclerotiorum in alfalfa seed fields of southeastern Washington.

Fall burning produced an intense surface fire that reduced numbers of sclerotia in an alfalfa seed field by >95%. The fire killed sclerotia in the dense layer of surface plant residue and scorched and killed sclerotia in the surface soil (0-2 cm). Only 14% of the collected surface soil sclerotia were viable after the fall burn. During the next 6 mo, the detectable number of sclerotia in surface soil samples declined from 246/m 2 in May and viability of sclerotia declined from 12 to 0%, respectively. Winter burning reduced surface residue and numbers of sclerotia but had no detectable effect in reducing the viability and survival of surface soil sclerotia (.)