Effects of flupropanate application on bare ground and broadleaf weeds when used to control Chilean needle grass in introduced pastures

Chilean needle grass (Nassella neesiana [Trin. & Rupr.] Barkworth) (CNG) is a serious weed with low palatability in extensive grazing enterprises of south-eastern Australia. Flupropanate is a slow-acting soil uptake herbicide that is used to control CNG. Although flupropanate is registered as a selective chemical, the selectiveness has been questioned previously. This paper examines the effect of flupropanate under three grazing regimes (set, strategic and no grazing) on the amount of bare ground and the basal cover of broadleaf weeds, at several CNG-infected sites in south-eastern Australia for 5-6 years after application. Under grazing, when flupropanate was effective in reducing CNG basal cover, it was associated with large increases in bare ground and broadleaf weed basal cover. After its application, the annual average basal cover was often 15%-25% for bare ground and 10%-20% for broadleaf weeds. This makes the application of flupropanate to control CNG problematic within extensive grazing systems of south-eastern Australia.