Title: Mission to kill off ryegrass in southwest Victoria
[Weekly Times, 03 Nov 2010, p. 82, by Peter Hemphill] -- WESTERN District farmers will run out of options to kill annual ryegrass in their crops unless they change their management practices. A survey of ryegrass populations in southwest Victoria has found 80 per cent of samples showed resistance to Group A "fops" herbicides and Group B sulphonyl urea weedkillers. The survey samples were randomly collected by Southern Farming Systems and analysed by the University of Adelaide as part of a national research program sponsored by the Grains Research and Development Corporation.
University of Adelaide weed specialist Chris Preston told farmers and farm advisers attending SFS’ AgriFocus field day at Lake Bolac the Group A "fops" and sulphonyl urea post-emergent herbicides were "pretty much gone" as options to control ryegrass in the Western District and growers needed to rely on other chemicals or management practices to control the weed in the future.
Dr Preston said the study did not pick up any trifluralin resistance in the ryegrass samples surveyed.He said among the "dims" chemicals, resistance to Achieve was also about 80 per cent, while resistance to Select was about 15-20 per cent. For the den" herbicide Axial, resistance showed up in about 60 per cent of samples. Dr Preston said the district had moved from having a relatively low level of herbicide resistance to quite high level of resistance in a short time.
"Why has that happened? Largely because the areas that were being sampled were those that had moved extensively into continuous cropping over the past decade. "And with continuous cropping in the no-till farming system, that means continuous herbicides. So, for individual farmers in this area, if you have paddocks continuously cropped over the past decade or so, you should expect to have Group A fops’ resistance and Group B resistance as well."
Dr Preston said growers should look at new herbicides with different modes of chemical action and look at integrated weed management options. What that means depends very much on your farm, what you are willing to do, what crops you want to grow and what rotations you want to have," he said.
Dr Preston said South Australian farmers adopted two key practices for ryegrass control. These were growing oats for hay, taking particular care to spray after hay making to stop regrowth of the weed. The second was to spray top pulse crops using paraquat. Dr Preston said another key was to rotate some of the new pre-emergent chemicals into farm management.
Weed alert: Chris Preston says herbicide resistance in ryegrass is rising in the Western District. Picture: GREG SCULLIN
