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1 January 2008 Glyphosate-resistant Horseweed (Conyza canadensis) Control Using Glyphosate-, Paraquat-, and Glufosinate-Based Herbicide Programs
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Field studies were conducted in 2005 and 2006 to determine the most effective chemical options within three individual herbicide-based burndown programs, glyphosate, paraquat and glufosinate, for controlling glyphosate-resistant horseweed in Mississippi. Burndown treatments were applied April 5, 2005 and March 15, 2006 to horseweed plants 15 to 30 cm in height. Glyphosate at 0.86 kg ae/ha alone provided 60 to 65% horseweed control 4 wk after treatment (WAT). Control 4 WAT ranged from 73 to 74% when the glyphosate rate was increased to 1.25 kg/ha. Glyphosate at 0.86 kg/ha applied in combination with 2,4-D at 0.84 kg ae/ha or dicamba at 0.28 ae/ha maximized control of horseweed (≥ 90%) 4 WAT and soybean yield. Horseweed control 4 WAT with paraquat alone at 0.84 kg ai/ha ranged from 55 to 63% and control did not improve by increasing the rate to 0.98 kg/ha. Addition of 2,4-D or dicamba to paraquat maximized horseweed control both years (78 to 89%), whereas soybean yield was maximized with addition of dicamba or metribuzin at 0.42 kg ai/ha. Glufosinate applied alone at 0.47 kg ai/ha resulted in at least 88% control of horseweed and maximized soybean yield. Results indicate that effective management of glyphosate-resistant horseweed can be obtained in glyphosate-resistant soybean in glyphosate-, paraquat-, and glufosinate-based preplant weed control programs.

Nomenclature: Carfentrazone, chlorimuron, 2,4-D, dicamba, flumioxazin, glufosinate, glyphosate, linuron, metribuzin, oxyfluorfen, paraquat, thifensulfuron, tribenuron, horseweed, Conyza canadensis (L.) Cronq. ERICA, soybean, Glycine max. (L.) Merr. DK 4763RR, AG 4801RR

Thomas W. Eubank, Daniel H. Poston, Vijay K. Nandula, Clifford H. Koger, David R. Shaw, and Daniel B. Reynolds "Glyphosate-resistant Horseweed (Conyza canadensis) Control Using Glyphosate-, Paraquat-, and Glufosinate-Based Herbicide Programs," Weed Technology 22(1), 16-21, (1 January 2008).
Received: 5 March 2007; Accepted: 1 September 2007; Published: 1 January 2008

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