chemical residue once cleared , and so do not provide any long-term protection against re-invasion by pests . Currently there are only two viable chemical fumigants available to the almond industry : phosphine and sulfuryl fluoride . Phosphine is the most common fumigant used in almond stockpiles . Its density is very similar to that of air , making it a highly mobile gas , and its distribution through stockpiles relies on passive dispersal , driven by changes in temperature and pressure . Phosphine movement in external fumigations , such as in covered stockpiles , may also be influenced by wind disturbance of tarpaulins which can result in uneven distribution of the fumigant . Sulfuryl fluoride is less commonly used and must be applied by a licenced fumigator specifically trained in its use . As it is almost three times as dense as air , sulfuryl fluoride may require a fan to ensure even distribution . Fumigation times for this product are , however , much shorter than those for phosphine .
Best-practice fumigation Two key requirements need to be met to ensure an effective fumigation :
Figure 1 . Tarpaulin-covered almond stockpile .
Correct dose As gases , fumigants fill the entire space being used for the fumigation . It is therefore essential to calculate the fumigant dose based on the volume of the whole storage space , not just the almonds . For almond stockpiles under tarpaulins this is generally the volume of the product . For sheds and silos however , the dose must relate to the volume of the whole shed or silo , regardless of whether it is full or half empty .
Sufficient duration Fumigants require time to work . Of the four life stages of almond insect pests , eggs and pupae are often hardest to kill . Their low rate of metabolism means that it takes longer for the fumigant to be absorbed and take effect , compared to adults and larvae . Almond stockpiles are relatively large , and most beetle and moth pests will be hidden within almond kernels , inside shells and hulls . Continued page 38
industry . australianalmonds . com . au
37