Multiple herbicide‐resistant Lolium rigidum (annual ryegrass) now dominates across the Western Australian grain belt

Abstract

Lolium rigidum (annual or rigid ryegrass) is a widespread annual weed in cropping systems of southern Australia, and herbicide resistance in L. rigidum is a common problem in this region. In 2010, a random survey was conducted across the grain belt of Western Australia to determine the frequency of herbicide-resistant L. rigidum populations and to compare this with the results of previous surveys in 1998 and 2003. During the survey, 466 cropping fields were visited, with a total of 362 L. rigidum populations collected. Screening of these populations with the herbicides commonly used for control of L. rigidum revealed that resistance to the ACCase-and ALS-inhibiting herbicides was common, with 96% of populations having plants resistant to the ACCase herbicide diclofop-methyl and 98% having plants resistant to the ALS herbicide sulfometuron. Resistance to another ACCase herbicide, clethodim, is increasing, with 65% of populations now containing resistant plants. Resistance to other herbicide modes of action was significantly lower, with 27% of populations containing plants with resistance to the pre-emergent herbicide trifluralin, and glyphosate, atrazine and paraquat providing good control of most of the populations screened in this survey. Ninety five per cent of L. rigidum populations contained plants with resistance to at least two herbicide modes of action. These results demonstrate that resistance levels have increased dramatically for the ACCase-and ALS-inhibiting herbicides since the last survey in 2003 (>95% vs. 70-90%); therefore, the use of a wide range of integrated weed management options are required to sustain these cropping systems in the future.

Metabolism-Based Herbicide Resistance and Cross-Resistance in Crop Weeds: A Threat to Herbicide Sustainability and Global Crop Production

“…Similarly, in Australia, there is much, albeit indirect, evidence that L. rigidum across vast areas exhibits both target-site resistance and metabolic cross-resistance to many herbicides (Llewellyn and Powles, 2001;Owen et al, 2007Owen et al, , 2014Malone et al, 2014). Our most recent work analyzing the in vivo metabolism of [ 14 C]diclofop in 33 multiply resistant L. rigidum populations collected in a random field survey (Owen et al, 2014) provides direct evidence that metabolic resistance is common (H.P.…”

Protocols for Robust Herbicide Resistance Testing in Different Weed Species

“…or Amaranthus spp. ), reduce the number of plants to [10][11][12][13][14][15], keeping the total number of seeds around 5,000 11 . 5.…”

“…Different approaches have been developed according to the aims, required level of accuracy, time and resources available, as well as the weed species considered [6][7][8][9][10][11][12] . However, when confirmation of the resistance status of a new weed biotype is required (i.e., a group of individuals that share several physiological characteristics, including the ability to survive one or more herbicides belonging to a particular group used at a dose that would normally control them), a robust whole plant bioassay needs to be performed in a controlled environment 4,11 .…”

Geographic Distribution of Ryegrass Resistent to the Clethodim Herbicide in Rio Grande do Sul1

“…Knowing the resistant species and the extension of the infested area provides insight on the severity of the problem, making it possible to determine the resistance handling and making the process of selection of resistant biotypes slower, helping in the reactive decision making process in the control of these populations (Owen et al, 2014). In addition, mapping the resistance enables the establishment of the resistance costs, the definition of public policies and the directed technical assistance.…”