New application methods for the use of phosphine to disinfest bulk grain

Abstract

1. With few compounds remaining cleared for use, fumigation as currently practised has limitations in dealing with infestation problems in floor-stored grain.

2. The fumigation of large bulks is costly and smaller stores are relatively more difficult to seal than larger ones of similar construction because of their greater surface area to volume ratio which permits a greater percentage loss of gas per unit time. The critical size of a storage facility for successful fumigation with phosphine varies widely with the type of construction but enclosures up to 1000 tonnes capacity are likely to give rise to problems, particularly under adverse wind conditions or at low temperatures.

3. Conventional phosphine formulations and the new Detia bag blanket have been tested using different dosing methods. Dosing both the grain surface and the ventilation ducts below the bulk improves gas distribution, particularly in large bulks.

4. Although formulations of aluminium phosphide release gas over a two or three day period, leakage of gas from smaller enclosures prevents an adequate amount of gas from remaining in the grain long enough to kill the more tolerant insect stages at low temperatures. At 5-10°C exposure periods need to be extended to at least 16 days.

5. Use of continuous gas flows from a cylinder-based mixture of 3% phosphine in carbon dioxide provides a means of sustaining sufficient levels of gas for a long enough period to successfully treat smaller stores without increasing cost.

6. The cylinder-based mixture also offers a means of using phosphine to treat 'hot spots' in large bulks.

7. Some progress has been made in developing a means of determining phosphine dosages by simple chemical detectors.