Challenges in using the biopesticide AF36 in pistachio orchards to reduce aflatoxin contamination
M. A. Doster (1), P. J. Cotty (2), R. D. Puckett (1), D. P. Morgan (1), T. J. MICHAILIDES (1). (1) University of California, Parlier, CA, U.S.A.; (2) USDA ARS, University of Arizona, Tucson, AZ, U.S.A.
The atoxigenic <i>Aspergillus flavus</i> strain AF36 (which is used in cotton fields to reduce aflatoxin contamination of cottonseed) was evaluated in two pistachio orchards in preparation for use in commercial pistachio orchards. The AF36 strain was applied as a wheat-AF36 product (the same product and rate as used in cotton fields) in a single annual application to the soil in late June or early July. The treatment substantially increased the level of the AF36 strain in the soil in both orchards, although the wheat-AF36 product was more successful in one orchard than in the other (>95% of the <i>A. flavus</i> isolates belonged to the AF36 strain in one orchard after a single application, while the other orchard needed two applications to get >80% AF36). In addition, the level of the AF36 strain remained relatively high for at least 2 years after the last application of the wheat-AF36 product. Application of the wheat-AF36 product did not result in increased levels of kernel decay. The application of the biopesticide AF36 to 1,200 ha of commercial orchards (Experimental Use Permit) resulted in 20-45% reduction in aflatoxin-contaminated pistachio samples (average for 4 years was 40% for the 1st and 2nd harvests). Furthermore, the AF36 reduced aflatoxin-contamination by about 55% (average of 3 years) in samples from the 2nd harvest, which can be contaminated usually with high levels of aflatoxins. Various challenges of AF36 application will be discussed during the presentation.
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