Aflatoxins, toxic metabolites produced by Aspergillus section Flavi, occasionally contaminate tree nuts in California, but due to strict regulations, they pose a high risk to international trade. The use of atoxigenic strains of A. flavus is a proven and registered method for aflatoxin control, but its efficacy depends on its timely sporulation and dispersal for toxigenic strains displacement. A. flavus AF36 Prevail sporulates abundantly in Californian orchards at temperatures over 25?. Earlier applications could be more effective, but it is unknown if the product will sporulate sufficiently. The effect of soil moisture and low temperatures on sporulation of A. flavus AF36 Prevail and Afla-Guard were evaluated in pots with soil in a growth chamber. Soil moistures were based on field capacity (FC) and temperatures were set according to maximum and minimum temperatures from May to July in the Central Valley, CA. Sporulation was determined by the percent of sporulating grains and a sporulation index (0-4). Results indicate that sporulation of AF36 Prevail is delayed under low soil moisture and low temperatures, while Afla-Guard has good sporulation even at minimum temperatures of 15?. AF36 Prevail has sporulation >80% and an index >1 at 16% to FC (21%) soil moistures and minimum temperature ?25?, while Afla-Guard reached these levels at the lowest temperatures. Good sporulation at low temperatures in earlier applications could be more effective on aflatoxin reduction.