Search

The introduction of harvest weed seed control (HWSC) techniques and associated machinery has enabled the routine use of an alternative weed control technology at a novel weed control timing in global grain cropping fields. Driven by the significant threat of widespread populations of annual ryegrass (Lolium rigidum) with multiple-herbicide resistance, in the 1990s Australian growers and researchers developed techniques to target, at grain harvest, the seed production of annual ryegrass and other important weed species. The HWSC approach to weed management is now routinely used by a majority of Australian grain producers as an integral component of effective weed control programs. Here we detail the development and introduction of current HWSC systems and describe their efficacy in Australian grain production systems. The use of HWSC has likely contributed to lower annual ryegrass population densities and thus mitigated the impacts of herbicide resistance as well as slowing further evolution of resistance. In addition, low weed densities enable the introduction of site-specific weed control technologies and the opportunity to target specific in-crop weeds with non-selective alternative weed control techniques. With an awareness of the evolutionary potential of weed species to adapt to all forms of weed control, there is an understanding that HWSC treatments need to be judiciously used in grain cropping systems to ensure their ongoing efficacy. The successful use of Australian developed HWSC systems has attracted global interest and there is now a considerable international research effort aimed at introducing this alternative weed control approach and timing into the world's major cropping systems. [ABSTRACT FROM AUTHOR]

Avena is a problematic weed of cropping regions of southern Australia and many areas of the world. In 2010, a random survey was conducted across 14 million hectares of the Western Australian grain belt to monitor the change in herbicide resistance levels by comparing resistance frequency results with a survey conducted in 2005. Screening Avena populations with herbicides commonly used to control this weed revealed that 48% of Avena populations displayed resistance to the commonly used acetyl-Co A carboxylase-inhibiting herbicides, which was lower than that found in 2005 (71%). The broad-spectrum herbicides glyphosate and paraquat provided good control of all Avena populations. Resistance to acetolactate synthase-inhibiting herbicides and to flamprop were detected for the first time in Western Australia in this survey. Therefore, a wide range of weed management options that target all phases of the cropping program are needed to sustain these cropping systems in the future. [ABSTRACT FROM AUTHOR]

Raphanus raphanistrum is a problematic weed, which has become increasingly difficult to control in Australian cropping regions. In 2010, a random survey was conducted across 14 million ha of the Western Australian grain belt to establish the frequency of herbicide resistance in R. raphanistrum and to monitor the change in resistance levels by comparing results with a previous survey in 2003. Screening R. raphanistrum populations with herbicides commonly used to control this weed revealed that most populations (84%) contained individual plants resistant to the acetolactate synthase-inhibiting herbicide chlorsulfuron, whereas 49% of populations also had plants resistant to the imidazolinone herbicides. Resistance to other mode of action herbicides (2,4-D (76%) and diflufenican (49%)) was also common. Glyphosate, atrazine and pyrasulfotole + bromoxynil remained effective on most R. raphanistrum populations. These results demonstrate that resistance to some herbicides has increased significantly since 2003 when the values were 54% for chlorsulfuron and 60% for 2,4-D; therefore, a wide range of weed management options that target all phases of the cropping program are needed to sustain these cropping systems in the future. Random surveys conducted in Western Australia have shown that herbicide resistance in major crop weeds is common and increasing. The latest survey on resistance in Raphanus raphanistrum revealed that 84% of populations were resistant to the ALS-inhibiting herbicides, 76% were resistant to synthetic auxins, and 49% to PDS inhibitors. Resistance in Raphanus has increased over the 12 year survey period and a wide range of management tools are needed to control this species. [ABSTRACT FROM AUTHOR]