Six years of survey data taken from 184 paddocks spanning 14 million ha of land used for crop and pasture production in south-west western Australia were used to assess weed populations, herbicide resistance, integrated weed management (IWM) actions and herbicide use patterns in a dryland agricultural system. Key findings were that weed density within crops was low, with 72% of cropping paddocks containing fewer than 10 grass weeds/m2 at anthesis. Weed density and herbicide resistance were not correlated, despite the most abundant grass weed species (annual ryegrass, Lolium rigidum Gaudin) testing positive for resistance to at least one herbicide chemistry in 92% of monitored paddocks. A wide range of herbicides were used (369 unique combinations) suggesting that the diversity of herbicide modes of action may be beneficial for reducing further development of herbicide resistance. However, there was a heavy reliance on glyphosate, the most commonly applied active ingredient. Of concern, in respect to the evolution of glyphosate-resistant weeds, was that 45% of glyphosate applications to canola were applied as a single active ingredient
Publication Authors: Martin Harries, Ken C. Flower, Craig A. Scanlan, Michael T. Rose, and Michael Renton.