The role of imidazolinone herbicides for the control of Bromus rigidus (rigid brome) in wheat in southern Australia

Five field experiments were undertaken over a three-year period in South Australia to investigate the efficacy of imidazolinone herbicides for the control of rigid brome in imidazolinone-tolerant wheat (Clearfield™, CLF). Imidazolinone herbicides, imazapyr, imazapyr plus imazapic and imazapyr plus imazamox applied post-emergence to imi-wheat (cvs. CLF-Janz and CLF-Stiletto) at the four-leaf stage, provided consistent and high levels of rigid brome control (≥87%). In contrast, applications of the alternative herbicide mesosulfuron-methyl (post-emergence) provided limited and variable control of rigid brome (11–67%). Furthermore, imidazolinone treatments caused a large reduction (P < 0.05) in rigid brome seed production (≤6 seeds m−2) as compared to mesosulfuron-methyl (461–3983 seeds m−2) and the non-treated control (2257–11 865 seeds m−2). Imazapyr plus imazapic provided consistent control of rigid brome and resulted in higher grain yields (28–45%) than wheat treated with mesosulfuron-methyl. Based on these results post-emergence applications of imazapyr, imazapyr plus imazapic and imazapyr plus imazamox to imi-wheat could play an important role in the management of rigid brome in southern Australia. However, the effect of these herbicides on existing and new cultivars of imi-wheat (multiple-gene resistance) and issues concerning persistence in low rainfall environments and crop damage on sandy soils require attention.