Aflatoxin contamination of peanuts results from invasion and growth of the fungi, Aspergillus flavus and A. parasiticus. Peanut pods develop in the soil where they are in contact with propagules of these ubiquitous fungi. When peanuts are subjected to drought conditions as pods are maturing, they become susceptible to contamination. A method of biological control of aflatoxin contamination was developed in which a competitive, nontoxigenic strain of A. flavus is applied to the soil to competitively exclude the toxigenic strains in the invasion of peanuts. The biocontrol product is comprised of conidia of the nontoxigenic strain coated onto the surface of hulled barley, which is applied to peanut fields during the middle of the growing season. After uptake of moisture the conidia germinate, grow, and sporulate, yielding a dominant population of the nontoxigenic strain in the soil. Several plot and field studies showed that aflatoxin in farmers' stock peanuts was reduced by 80 to 90% with this technique. The patented technology was licensed by a company that markets the biocontrol product under the trade name, afla-guard®. In 2004, the U. S. Environmental Protection Agency issued a Section 3 registration for use of afla-guard® to control aflatoxin contamination in peanuts. Analyses of peanuts from the first commercial use of afla-guard® in various locations in Georgia and Alabama showed aflatoxin reductions averaging 85% in farmers' stock peanuts and as high as 98% in shelled stock.