Technical Abstract: Biological control of aflatoxin contamination of peanuts can be achieved by applying nontoxigenic strains of Aspergillus flavus and A. parasiticus to soil around peanut plants. In the majority of studies that have demonstrated the efficacy of this process, nontoxigenic strains have been applied in a formulation produced by solid state fermentation of those strains on a sterile small grain, such as rice. Production of commercial-scale quantities of a biocontrol formulation by solid state fermentation is expensive and time-consuming because the substrate must be sterilized, inoculated, fermented 1-2 days, and dried at relatively low temperature. An alternative method for producing biocontrol formulations has been developed in which hulled barley or rice is spray-coated with conidia of the nontoxigenic strains that are suspended in oil. The coating technique eliminates the need for sterilization and drying of the substrate, and it can be readily scaled up to produce a biocontrol formulation at a rate of several tons per hour. Field experiments were conducted for three years to compare efficacies of the coated formulations of hulled barley and rice for reducing preharvest aflatoxin contamination of peanuts with that of solid state-fermented rice. Conditions of late-season drought, which are conducive for preharvest aflatoxin contamination, occurred in one of the three years, and all three formulations produced significant reductions (77-87%) in aflatoxin contamination compared with untreated controls. Results suggest that the coating method is preferable to solid state