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Post-harvest ideal time for stored grain fumigation

Within three weeks of the completion of harvest is the best time for a grower to fumigate stored grain to control insect pests, according to grain storage expert Ben White.

Mr White is a Western Australia-based member of the Grains Research and Development Corporation (GRDC) grain storage extension team.

He said grain was warm in summer and insect activity was high in warm conditions so fumigants would work rapidly and effectively.

Mr White said a clean start was a good start in preventing insect damage and preserving grain quality and growers ideally should have washed silos and applied structural treatments, such as diatomaceous earth (DE), prior to silos being filled with grain.

“All grain and grain dust residue should be removed from the storage site, including from grain hoppers and any steel silo support structures, and weeds around the storage site should be removed,” he said.

Mr White said fumigation should only be carried out in a pressure-tested sealable silo.

“Fumigation in silos with leaks may appear successful when some dead adults are found, but many of the eggs, pupae and larvae are likely to survive and will continue to develop and reinfest the grain,” he said.

“These partial kills are often worse than no kill at all because the surviving insects are likely to be those that carry increased phosphine resistance genes.

“Under-dosing risks increasing the number of insect populations carrying the genes for phosphine resistance and this has serious consequences for the industry.”

Phosphine is the most commonly used fumigant to control stored grain pests in Australia but other options include nitrogen and carbon dioxide.

“Each of the alternatives to phosphine still requires a gas-tight, sealable silo and are currently more expensive than using phosphine, but offer an alternative for resistant pest species,” Mr White said.

Mr White said if aeration cooling fans were fitted to grain storage silos, growers could operate these again after a fumigation period of seven to 10 days.