Title: Microwaves to cook away weeds - RIRDC weeds program
Microwave technology similar to that used in household kitchen ovens is being tested as a new form of selective weed control. Dr Graham Brodie, of the University of Melbourne, is leading a research project to develop a prototype machine that destroys weeds at a cost comparable to conventional chemical methods. The research project is funded by the Rural Industries Research and Development Corporation (RIRDC) who manage the Australian Government’s National Weeds and Productivity Research Program.
The prototype system, which is based on a modified microwave oven, using a horn antenna to apply microwave energy to weeds.
“It is possible to watch plants irreversibly wilt after a few seconds of microwave treatment as their cells soften due to microwave heating,” Dr Brodie said. “Microwave radiation affects plants by softening and transforming cellulose – one of a plant's most important molecules – leading to the collapse of the structures that carry water through their stems, ultimately leading to plant death. “Microwave energy can be focused onto individual plants, without affecting adjacent plants, which would be very useful for in-crop or spot weed control.”
Microwave energy has also been shown to kill roots and seeds that are buried to a depth of several centimetres in the soil. “Unfortunately, microwave energy cannot selectively heat the seeds in the soil, so microwave-base seed treatment must also heat the bulk soil around the seeds in order to kill the weed seeds embedded in it. This takes a lot of energy. “It takes far less microwave energy to kill growing plants above the ground, but preliminary studies indicate that plant treatment still requires about 10 times the energy that is embodied in conventional chemical systems to achieve effective weed control.”
Dr Brodie’s research project aims to develop a microwave application system that is more energy efficient and provides a viable weed control alternative to counter the problem of herbicide resistance to conventional chemicals.
“Microwave-based weed treatment is not affected by wind and rain after treatment and so this extends the application periods compared to conventional spraying methods,” Dr Brodie said. “This treatment leaves no residue in the field or on the plant, so there are no withholding periods.”
While Dr Brodie’s initial trials will use a normal kitchen microwave oven, the research program will also test new techniques for applying microwave treatments. The research team then hopes to develop a prototype carrying an industrial-scale microwave system for use in field trials before conducting an economic and environmental assessment of the procedure.
RIRDC is providing around $12.4 million (GST inclusive) to more than 50 new projects under Phase 2 of the National Weeds and Productivity Research Program. These projects include:the use of a biodegradable weed mat made of hemp fibre that both smothers weeds to death and adds organic matter to the soil
the use of ‘suppressive plants’ to limit parthenium weed
the use of aerial imagery to detect and monitor weed populations
new machinery to destroy weed seeds at the point of crop harvest.
More information on the weeds research projects being funded by the Australian Government is available at rirdc.gov.au/weeds.
