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Microwave brings quick death

The technology that heats the common kitchen microwave oven has been adapted to deliver a chemical-free solution to Australia’s weed problems. University of Melbourne senior lecturer Dr Graham Brodie has developed a fully operational prototype that can successfully focus microwave energy at ground level, killing weeds within seconds. “Herbicide resistance and environmental concerns already limit the chemical options available for weed management,” Dr Brodie said. “In looking for alternative weed treatments, we have found that microwave treatment is immediate, chemical-free and leaves no residue at the treatment site.” Weeds are one of the major threats to Australia’s primary production and to the natural environment. It has been estimated that weed cost Australian agriculture more than $4 billion dollars a year, including control costs and lost production. Interest in the effect of microwaves on plant health dates from the 1920s, but recent studies shifted away from trying to treat seeds in the soil and instead targeted plant seedlings. The concentration of microwave energy collapses the structures within the weeds that carry water through their stems. Depending on the amount of energy applied, irreversible wilting and subsequent death occurs within seconds of the microwave exposure. Dr Brodie’s research initially tested a 600-watt kitchen microwave, before developing an 8kW field unit that has been tested in the paddocks at the university’s Dookie campus. A series of four microwave horn antennae, each just 11cm wide and transmitting 2kW of microwave energy, were fitted to a trailer to focus their transmission solely on the weeds in the inter-row space of agricultural field crops. Dr Brodie said that in a broadscale agricultural operation, many antennae could be mounted on a tractor trailer at spacings in line with whatever crop was being treated. Treatment could take place regardless of weather conditions, would successfully kill herbicide-resistant species and would not limit production schedules with withholding periods at the site after treatment. “There is potential to develop an industrial 15kW unit which could operate in broadacre situations at near the speed of current chemical spray applicators, with each weed requiring less than a second of exposure to the microwave transmission,” he said. “Microwave weed management has the potential to be applied throughout Australia to manage weeds not just in agricultural enterprises, but on public land, sporting facilities and in landscape gardening. “A smaller 1-2kW unit could also be designed for use by householders if the market supported the concept.” The prototype microwave system is now operational and can be demonstrated to interested parties who may wish to use the technology in commercial systems. Dr Brodie’s research during 2011-12 was conducted as part of the Australian Government’s National Weeds Research and Productivity Program, administered by the Rural Industries Research and Development Corporation (RIRDC). The Commonwealth provided $12.4 million to RIRDC to support more than 50 research projects, with the program ending on June 30. The funding covered the first two years of a five-year National Weeds and Productivity Research Program R&D Plan for 2010-15. The RIRDC program invested in projects aimed at improving knowledge and understanding of weeds, as well as delivering new treatments, with 11 research projects dealing directly with herbicide resistance issues.

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