Navel orangeworm with almonds
Navel orangeworm with almonds.

NOW control, AF36 good tools to suppress aflatoxin growth in almond

NOW damage in almond has been holding steady for the past several years, but more growers are finding higher damage rates.

With its Pre-Export Checks (PEC) program in effect, the California almond industry is aiming to ensure aflatoxin contaminated shipments don’t reach the market.

Growers also need to do their parts to suppress Navel orangeworm populations in orchards to keep the pest from vectoring molds which cause aflatoxins on almonds.

Both efforts are valuable this year as NOW trap counts and nut damage percentages are much higher.

Aflatoxins are known carcinogens produced by molds, primarily of the Aspergillus genus. Mold spores are found in the soil and dust, and can be transferred to almond kernels by Navel orangeworm (NOW) feeding.

Almond Board of California (ABC) Agricultural Affairs Director Bob Curtis says the industry wants to keep the aflatoxin reject percentage in almonds to less than 1 percent, but this takes a concerted effort by growers and handlers to minimize contamination.

Not all insect damaged nuts are contaminated with aflatoxin, Curtis notes. While NOW feeding does not guarantee aflatoxin development on almonds, industry leaders say it’s important to take steps to reduce orchard NOW populations to ensure food safety and quality.

Tim Birmingham, the ABC’s director of quality assurance industry services, says it starts at the orchard level. This means growers must practice good sanitation by shaking mummy nuts to the ground during the winter and disking it into the soil.

Higher rainfall amounts last fall and winter made this difficult, Birmingham says, resulting in more insect pressure. Mummy nuts left on the tree had the potential to become incubators for this summer’s NOW population.

NOW damage in almond has been holding steady for the past several years, but more growers are finding higher damage rates. Increased damage could lead to higher aflatoxin levels unless measures are taken at harvest to prevent mold growth. Birmingham says efforts include controlling moisture at harvest and stockpiling.

Mel Machado, Blue Diamond’s director of member services, says almond growers were challenged to get last winter’s shake completed for NOW control. Going into this year’s growing season there was a potential for a high NOW population. A prolonged hull split due to July heat shot the trap counts higher and growers have dealt with more insect damage than normal.

Even with good orchard sanitation, timely sprays, and early harvest, Curtis says growers can suffer ‘NOW train wrecks’ when the practices are not followed in neighboring almond orchards.

In addition to NOW control, growers have another tool to suppress aflatoxin growth in orchards. Birmingham says the biocontrol agent AF36 was recently approved for use in almonds. Research in aflatoxin control in pistachios by the University of California found that atoxigenic strains of Aspergillus flavus will out compete toxic strains and lower the percentage found in orchard soils.

The atoxigenic strain AF36 is carried on wheat and applied to orchard floors every other year. Studies over the last three years found nuts from AF36 treated orchards were less likely to be contaminated by aflatoxins.

Birmingham and Curtis also express confidence that the more recent voluntary sampling program for handlers will ensure a safe product this year.

The PEC program was developed by the California almond industry to provide an aflatoxin sampling plan equal to the one used in the European Union for incoming almond shipments.

Due to European Union confidence in the almond industry’s 2007 Voluntary Aflatoxin Sampling Plan, the EU, a large importer of California almonds, removed the special measures requirements for California almonds and now allows the voluntary PEC program to handle almond sampling and analysis.

PEC requires specific and documented sampling at USDA approved facilities. Shipments are then tested at a reduced frequency on arrival, showing EU confidence in the product.

Almonds are only the second commodity besides wheat in a pre-certification program, says Birmingham.

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