Figure 3: Four almond storage types being investigated (clockwise from top left): (i) outside uncovered; (ii) shed; (iii) outside clear cover; and (iv) outside white over black cover
In addition to the type of covering, there is also a difference in the location within the stockpile where Aspergillus growth and aflatoxin production is most severe. This is also related to environmental conditions where the top and outer layers are either exposed to rainfall (uncovered stockpiles), or conditions fluctuate more markedly than those in the middle and basal layers. Consequently, the top and outer layers again accumulate moisture and have an increased incidence of Aspergillus (Figure 5) (and bacteria) growth and aflatoxin production (Figure 6). Australian and Californian R&D into stockpiles indicates the following points are considered best management in minimising Aspergillus growth and aflatoxin production: • Avoid the use of clear covers to minimise temperature fluctuations and condensation. Of the covers tested to date, B&W covers are recommended. • Do not stockpile if either the hull moisture or kernel moisture exceeds 13% or 6%, respectively. • Orienting the stockpiles in a north/south direction is preferable to achieve a more stable environment. • Smooth the tops of stockpiles to avoid concentration of condensate.
Figure 4: Condensation under clear tarp stockpiles