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AF36, Biocontrol Agent for Aflatoxins, Now Approved for Almonds


Early July application proved highly effective in field tests

Decades of research investigating methods for reducing aflatoxin contamination have led to the discovery of the atoxigenic Aspergillus strain, referred to as “AF36.”

Recently approved by EPA and California Department of Pesticide Regulation, AF36 may help to significantly reduce aflatoxin levels.

Aflatoxins are naturally occurring, “toxigenic” mold strains produced by certain strains of Aspergillus molds. AF36 is also an Aspergillus mold, but this naturally occurring strain does not produce aflatoxin and therefore is “atoxigenic.”

AF36 is carried on a sterilized sorghum seed and is found in the soil of fig, pistachio and almond orchards. When applied, this atoxigenic strain out-competes and displaces existing toxigenic mold strains in the orchard floor and the tree canopy, and therefore acts as a biological control used to reduce the potential for aflatoxin.

HullsplitEffective tool

Dr. Themis Michailides, plant pathologist at the UC ANR Kearney Agricultural Center, can attest to its efficacy. His extensive research in aflatoxins was integral to EPA registration of AF36 products for tree nuts.[1]

Field studies in both pistachios and almonds have been impressive. In a study of commercial pistachio orchards with AF36 applications occurring once-per-year from 2009–2011, Michailides and team observed aflatoxin reductions from 20–45%, with a 40% total reduction at the end of the study.

How to apply

Timing: In experimental use on almonds, AF36 proved most effective when spread on moist soil in early July. Ultimately, though, application should be timed around hullsplit. If you know when to expect hullsplit, you should plan to apply about one to two weeks before. You want to have maximum sporulation of the biocontrol during the hullsplit stage.

Amount: The proper application rate is 10 pounds per acre.

Placement: AF36 should be applied within the berm area of the orchard, not in row middles, so that it will be reached by the irrigation system.

Proper irrigation: Irrigation is required directly after application. The AF36 Prevail product will not sporulate without moisture and can fail if there is too much moisture. Aim for soil moisture levels around 13–18%. Proper placement within the berm, close to the irrigation system, will ensure it is successfully activated.

NOW management still essential

While the AF36 Prevail product shows promise, it is essential to keep up with NOW and pest management as NOW damage still presents one of the greatest threats to aflatoxin development in the crop.[2]

Growers can minimize the risk of aflatoxin contamination by using multiple IPM practices: reducing overwintering populations of NOW through winter sanitation; timely harvest; in-season sprays and employing mating disruption.

Step-by-step videos and product sourcing

To learn more about AF36 and its application, watch two short videos produced by California Pistachios. While the videos feature AF36 in pistachio orchards, the information is useful and accurate for almond growers, as well.

AF36 Prevail is available in California from Western Milling. For product information, contact Jeff Chedester, seed business manager, at (559) 978-0725.

[1] Doster, M.A., Cotty, P.J., and Michailides, T.J. 2014. Evaluation of the atoxigenic Aspergillus flavus strain AF36 in pistachio orchards. Plant Disease 98:948-956.

[2] Palumbo, J.D., Mahoney, N.E., Light, D.M., Siegel, J., Puckett, R.D., Michailides, T. J. 2014.  Spread of Aspergillus flavus by navel orangeworm (Amyelois transitella) on almond. Plant Disease 98:1194-1199.

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