Chemical control of flaxleaf fleabane (Conyza Bonariensis L. Cronq.) in winter fallows.

Flaxleaf fleabane (Conyza bonariensis L. Cronquist) has recently become a problem weed in the northern grain region of Australia. Herbicide control of this weed has been variable. Experiments were conducted to identify effective herbicide control options for flaxleaf fleabane in winter fallows. Research showed that effective fleabane control in the fallow cannot be achieved with any single herbicide treatment, even with the knockdown herbicides such as glyphosate and paraquat + diquat. A combination of herbicides with different modes of action is needed to achieve effective control. The addition of a suitable mixing partner, especially auxins, such as 2,4-D and dicamba, to glyphosate improved control efficacy. A 'doubleknock' technique, sequential application of glyphosate followed by paraquat + diquat, also achieved 96% control. Three non-glyphosate mixtures, 2,4-D amine + metsulfuron methyl, Amitrole T® either mixed with 2,4-D ester or 2,4-D amine, also provided > 94% control. Residual herbicides atrazine or mixture of atrazine + metolachlor at higher rates provided effective long-term (five to six months) control of flaxleaf fleabane in winter fallows. This preliminary study identified some post-emergence and residual herbicides that can provide effective control on flaxleaf fleabane, which will be useful for the development of an integrated weed management package for this weed.