Control of Flaxleaf Fleabane (Conyza bonariensis) in Wheat and Sorghum

Flaxleaf fleabane is a difficult-to-control weed in dryland minimum tillage farming systems in the northeast grains region of Australia. Experiments were conducted between 2003 and 2005 to identify effective control strategies on flaxleaf fleabane in wheat and sorghum. A preplant application of chlorsulfuron at 15 g ai/ha in wheat controlled flaxleaf fleabane >= 90%. The efficacy of early postemergent applications of metsulfuron methyl at 4.2 g ai/ha varied between years. However, the flaxleaf fleabane was controlled > 85% with metsulfuron-methyl at 4.2 g ai/ha plus MCPA at 420 g ae/ha plus picloram at 26 g ae/ha, or metsulfuron methyl followed by late postemergent 2,4-D amine at 300 g ae/ha. In sorghum, a preplant application of glyphosate at 900 g ae/ha plus 2,4-D amine at 900 g ae/ha or dicamba at 500 g ae/ha at 1 mo before sorghum planting provided >= 95% control. Preplant atrazine at 2,000 g ai/ha controlled flaxleaf fleabane 83 to 100% in sorghum. At-planting atrazine at 2,000 or 1,000 g ai/ha can he applied to control new emergence of flaxleaf fleabane and grasses, depending on the weed pressure and spectrum. Flaxleaf fleabane reduced sorghum yield 65 to 98% if not controlled.