Multiple herbicide-resistant wild radish (Raphanus raphanistrum) populations dominate Western Australian cropping fields.

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]