Crop rotations help prevent resistance woes

Dr Christopher Preston

Dr Christopher Preston

WEED control due and resistance to post-emergent herbicides is becoming a challenge throughout the Riverina.

New science and an identification of alternative techniques will be discussed by University of Adelaide associate professor in Weed Management, Dr Chris Preston at a Wagga meeting on February 15.

Dr Preston identified resistance to the chemical clethodim as being a challenge. “The Wagga meeting will allow us to discuss better management of grass weeds in canola … resistance to post-emergent herbicides is making grass wee control more difficult,” he said. A range of research – funded by the Grains Research and Development Corporation – has investigated strategies that work.

“These include the combination of pre-emergent herbicides and hybrid canola,” he said. Despite the arising resistance issues Dr Preston said generally southern NSW was fairing better than South Australia and Victoria.

“There is still quite a bit of pasture and that means farmers use less herbicide, however there are many farmers who continually crop in Southern NSW and these are the ones facing the resistance problems,” he said.

“Clethodim is starting to fail.” Dr Preston said there were some alternative herbicides such as Gramoxone, which could be used to replace glyphosate in some instances. “A better strategy has been to adopt rotations that provide competition against weeds and allow for seed set control tactics to be employed,” he said. “Wind rowing (and burning in) canola is an example of what can help to reduce annual rye grass,” he said.

Meanwhile, Dr Preston said most canola volunteers germinated during the summer period or in autumn in the year after harvest. “These can easily be controlled by using knockdown mixtures containing effective herbicides in cereal crops,” he said.

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