Battling the bugs

by Teresa Acklin
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The search for options to methyl bromide to kill grain insects includes different fumigants, new technologies for aeration.

   The grain industry is heavily reliant on the fumigants phosphine and methyl bromide to control insects. The use of methyl bromide will soon be restricted because it is an ozone-depleting chemical, and evidence is increasing that insects are becoming resistant to phosphine.

   In a project supported by Australian grain growers through the Grains Research and Development Corporation, scientists at Australia's Stored Grain Research Laboratory are looking for alternative fumigants. If the research is successful, the grain industry could become less reliant on phosphine and may be able to rapidly disinfest grain by means other than methyl bromide.

   The project, led by Dr. Jim Des-marchelier, has investigated three fumigants: carbonyl sulphide, a new product that is being tested on grain; carbon disulphide, which has a long history of use as a grain fumigant; and ethyl formate, currently used on dried fruit. Laboratory studies have shown that none of these three compounds, when used as a fumigant, has any effect on the baking quality of wheat.

   For the three fumigants to be accepted and registered for use on grain for human consumption, regulatory authorities and the industry require comprehensive trials under commercial conditions. These call for storage, milling and baking trials for wheat.

   S.G.R.L. scientists obtained a permit from Australia's National Registration Authority to conduct preliminary trials. The trials used wheat in three 50-tonne bins on the S.G.R.L. site with laboratory staff as qualified fumigators.

   One silo was fumigated with each of the fumigants, and samples of the grain were subsequently collected for analysis by the Bread Research Institute in Sydney. The grain was milled and baked into products such as noodles, bread and sponge cakes for further testing.

   For all three fumigants, the initial results showed good control of three species of test insects used with residues below the experimental limit set by the NRA. The plan is to repeat these trials using barley, in association with the malting and brewing industries.

   On the basis of the combined wheat and barley data, regulatory approval will be sought for large-scale field trials to evaluate the effect of the fumigants on another cereal grain, such as oats, and on canola. The aim is to obtain general permission to use these fumigants.

   Although chemical methods for pest control in stored grain can be highly successful, consumers are becoming more concerned about pesticide residues in foods, and many markets will no longer take grain that has been treated with chemical protectants. That's why S.G.R.L. scientists also have been taking a new look at some older techniques.

   Forced-air aeration, for example, is a powerful and well-known tool for preserving stored grain, but its use has declined over the last 20 years.

   “This is largely because of the success of chemical protectants and fumigants for insect control and the perception that aeration is a difficult and expensive technique that cannot meet industrial ‘nil' tolerance standards for insect infestation,” said S.G.R.L. project leader Jonathan Banks.

   Now, S.G.R.L. researchers, by applying the latest process control technologies, have dramatically enhanced the effectiveness of aeration. The Smart Aeration and Programmable Microprocessor and Monitoring (PMCAM) system, working through a computer and modem, allows remote monitoring of grain storage conditions and monitoring and control of equipment such as aeration fans.

   PMCAM senses the ambient air and conditions in the stored commodity, and turns fans on and off as needed. Aeration becomes a much more precise, safe and cost-effective method of grain preservation.

   Extensive field trials of Smart Aeration have been carried out in collaboration with the Bulk Handling Companies in Australia. According to Dr. Banks, the success of field trials of PMCAM has increased the acceptance and application of aeration cooling to safely store wheat and other commodities. Around 40 PMCAM trial units are now out in full scale use across the country.

   Dr. Banks said the applications of the system were being extended to include remote monitoring of fumigation of grain bulks and electronic insect detection. Smart Aeration allows for improved management of aeration and the combination of aeration with other grain protection strategies.

   “The Smart Aeration project has been successful with full scale industrial trials demonstrating that strategically applied aeration plus a ‘minimal extra,' such as a single phosphine fumigation, can produce insect and residue-free grain that meets export market specifications, at about one-third of the power costs currently incurred,” Dr. Banks said.

   PMCAM and Smart Aeration research was funded by growers through the Grains Research and Development Corporation, the Bulk Handling Companies and the Australian Wheat Board.

   This article is based on two reports published in the August 1997 issue of Stored Grain Australia, the newsletter of the Stored Grain Research Laboratory, Canberra, Australia.