Farm Progress

A clean, dry orchard floor as harvest approaches is an essential food safety step for almond growers.

August 13, 2013

4 Min Read
<p> Dr. Themis Michailides (right) examines an application of AF36 in a pistachio orchard with Dr. Mark Doster, staff research associate with the plant pathology lab at UC&rsquo;s Kearney Agricultural Center, Parlier. The researchers are working on the atoxigenic Aspergillus species in both pistachio and almond orchards.</p>

Maintaining a clean, dry orchard floor as harvest approaches is an essential step in a food safety program for almond growers. Because harvested almonds are in contact with the orchard floor for an extended time, growers must make all efforts to minimize the introduction and survival of pathogens that could contaminate the crop. Research in the produce industry has shown that one of the key sources of pathogens can be an animal operation adjacent to the orchard.

Risk of Adjacent Facilities

At the Almond Board of California’s recent Food Quality and Safety Symposium, Dr. Trevor Suslow, University of California, Davis, shared his experiences with controlling pathogens in the produce industry. Although not an “apples-to-apples” comparison, his experience in crop production inputs and practices on microbial food safety can help our industry to better understand potential areas of concern that we may want to explore further.

According to Dr. Suslow, when you think about food safety, you really need to pay attention not only to your own practices, but also those of your neighbors.

Adjacent operations can add diverse risk factors that may be difficult to control. Studies have clearly shown that produce operations adjacent to animal operations can easily become contaminated with pathogens.

Dr. Suslow cited research that showed pathogens from an animal feeding operation can travel by air and water onto a production field. Animals housed in drylot kick up aerosols, or “heifer dust,” which can be carried by wind or in fog onto adjacent fields or into canals that supply irrigation water. This may lead to soil contamination, and once it arrives on the soil, it is difficult to manage.

Bird traffic between a dairy waste lagoon and production fields are another means by which pathogens are known to be introduced, and cattle pest flies may also be a source of contamination.

Manure and Compost

Crop inputs such as manure and compost can be a major risk factor if controls are not in place to ensure the  inactivation of microbial pathogens prior to field application. He pointed out that it is still common to store non-composted manure near orchards, which can be a source of microbial contamination through wind, wildlife and runoff. Dr. Suslow shared data showing that once a field is contaminated, it may be difficult to rid it of the pathogen.

Aflatoxin Prevention Tool

Another food safety risk in almond orchards is aflatoxin, which is produced by the fungus species Aspergillus flavus and A. parasiticus. Dr. Themis Michailides, University of California, Davis, plant pathologist, shared exciting information at the symposium that may soon result in a new tool for growers to combat aflatoxin development in the orchard.

According to Dr. Michailides, 50 percent of the strains of A. flavus and A. parasiticus found   in in the orchard are naturally atoxigenic — that is, they do not produce aflatoxin.  When applied to orchards, the atoxigenic strain of Aspergillus flavus, AF36, displaces the aflatoxin-producing strains, thus reducing the level of aflatoxin in the product.

Field trials in almonds are currently underway at the Nickels Soil Lab in Arbuckle, and show that AF36 is effective in displacing toxigenic strains. In one research trial, AF36 was placed on wheat grains and distributed on an orchard floor where the soil was wet from irrigation. Over a period of two years, the level of AF36 rose from 6 percent to 83.9 percent, while in the untreated area, the naturally occurring atoxigenic strain went from 1.1 percent to only 5.3 percent in the same time.

AF36 is now in the second year of commercial use in the pistachio industry. Next steps will include commercial almond orchard field trials. According to Dr. Michailides, data has been submitted to EPA for registration. He expects the cost of material to be about $7 per acre, once AF36 is registered for use on almonds.

Continued advancements such as these in food safety technology and implementation will help the California Almond industry to build a quality reputation among buyers, food manufacturers and ultimately, consumers around world. The Almond Board website has many resources available to both growers and handlers to assist in these efforts. Go to


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