Management of flaxleaf fleabane (Conyza bonariensis) in lucerne pastures

Pasture has been an integral component to the success of mixed farming systems in southern Australia. However, heavy infestation of fleabane in pasture paddocks has become common in southern NSW. Currently no registered products are available for fleabane control in lucerne based pastures, thereby representing a real challenge to control fleabane in pastures. The present study showed that most treatments applied in early July did not achieve commercially acceptable control on small fleabane. Addition of suitable Group C herbicides such as atrazine and simazine to Paraquat provided excellent control on small fleabane and on subsequent emergences. These mixtures gave better control on fleabane when compared to the standalone treatment of atrazine or simazine. Another trial in lucerne pastures to target mature fleabane after grazing in early December showed that only a few double-knock treatments gave excellent control of fleabane. These included 2, 4-DB ± flumetsulam (or ± a Group C herbicides) followed by 7 days later Paraquat ± atrazine (or simazine). Grazing by itself is not effective, as it only delayed the growth and development of fleabane. The fleabane regrowth after grazing requires follow-up herbicide applications, otherwise the fleabane will flourish as a result of little competition.This research indicates that effective fleabane control should target small fleabane using residual herbicides in winter. Alternatively, mature fleabane should be grazed by sheep and followed by herbicide applications. However, it should be noted that many herbicide treatments caused significant damage to the pasture species.