Combining the Benefits of Cooling and Phosphine Fumigation to Meet the Biosecurity Challenge Posed by Grain Insects

摘要

Two of the best options for Australian farmers to manage insects in stored grain are aeration cooling and phosphine (PH3) fumigation. Farmers are being encouraged to use aeration to preserve grain quality and to slow insect population growth. However, insects are surprisingly difficult to kill with cold and the temperatures achieved using aeration in Australia are unlikely to result in adequate control. Therefore, the best strategy would be to combine aeration and fumigation to meet market demands for grain free of live insects. This paper summarises laboratory and field research addressing the question of whether Australian farmers can successfully fumigate cool grain. Published data show that there are minimal differences between the most PH3-resistant Australian strains of the rice weevil (Sitophilus oryzae) and lesser grain borer（Rhyzopertha dominica) at 25~C, but we found that resistant rice weevils were much harder to control in cool grain. Loss of gaseous PH3 through sorption into the grain kernels can reduce the amount of PH3 to which insects are exposed, particularly in a highly sorptive grain such as sorghum. We found that sorption was lower in cool sorghum grain resulting in higher average concentrations. Sorghum was less sorptive the longer it was stored before being fumigated for the first time, also resulting in higher average concentrations. These trends were observed to a lesser extent in wheat. These laboratory results suggest that farmers would achieve the best results by cooling the grain first and fumigating later. Field trials have been conducted in silos of up to 158 m3 capacity in three states,indicating that fumigating cool grain is a useful option for farmers who have sealable silos.