Determining the best management techniques for almond harvest and stockpiles has been the subject of several years’ research supported by the Almond Board of California. The findings from this research were compiled and presented at the 2010 Almond Conference by Butte County Farm Advisor Joe Connell and Bruce Lampinen, UC Davis Extension specialist, who led the work.

Earlier research, in the late 1970s and 1980s, demonstrated the value of timely harvest for crop quality, particularly related to insect damage. Current emphasis is on stockpiling and crop moisture content to avoid mold growth in piles, particularly the Aspergillus fungus that produces aflatoxin.

Researchers have found that stockpiling in-hull almonds at a moisture content greater than 7 percent leads to a relative humiditiy (rH) within the stockpile of more than 70 percent, which is the maximum allowable rH for almond storage. This amount of moisture is of greater risk in the outer portions of piles, where temperature fluctuation, condensation on tarps and moisture accumulation can be significant.

Molds such as Aspergillus are more likely to grow in these marginal areas than in the rest of a high-moisture-content pile, where the equilibrium rH within the pile comes to a steady state below the maximum limits recommended for storage.

As a practical guideline, the researchers suggest that almonds should not be stockpiled if either the hull moisture content exceeds 13 percent, or the kernel moisture content exceeds 6 percent.

Timely harvest

The first step to maintain quality is to harvest at the optimum time. Shaking should begin when there is 100 percent hullsplit of the lower interior nuts. All nuts in the lower canopy should be at least at stage “b3” and beyond (see “Integrated Pest Management for Almonds, Second Edition,” page 7, for a description of hullsplit stages). At this stage of maturity, nuts in the upper-outer portions of tree canopies will be drier, all nuts will have achieved maximum dry weight of oils and carbohydrates, and there will be maximum nut removal.

Delayed shaking risks higher worm damage (and potential for aflatoxin contamination), particularly when the crop is exposed to a preharvest third generation of egg-laying by navel orangeworm.

Harvesting too early will increase the potential for ant damage because the crop will take longer to dry on the orchard floor. Early shaking also increases the potential for quality problems, such as ‘sticktight’ hulls, foreign material and damage to kernels during hulling.

A third risk is moisture as a result of rain, especially in a year when crop maturity is delayed. If rain is in the forecast, it is best to leave the crop in the tree rather than to begin shaking. If the crop is already on the ground, be sure to provide access for conditioning — blowing out leaves and debris — and for turning to facilitate drying. Nuts down the tree row should be moved toward the middles (drive rows) for access.