Horseweed (Conyza canadensis) Control in Conservation Tillage Cotton (Gossypium hirsutum)

Abstract

Horseweed is a major weed in conservation tillage production systems. Herbicides were evaluated for horseweed control at two growth stages, rosette and 10- to 15-cm tall. Horseweed was controlled at the rosette stage with the 2,4-D ester, 2,4-D amine, dicamba, 2,4-D plus glyphosate, and glyphosate. Higher rates were needed for control at the 10- to 15-cm stage. Paraquat did not effectively control horseweed at any stage.

Control of glyphosate-resistant Canada fleabane [Conyza canadensis(L.) Cronq.] with preplant herbicide tankmixes in soybean [Glycine max. (L). Merr.]

“…This may be due to a higher weed density at this site and possibly poorer spray coverage. Glyphosate plus 2,4-D provided 92% control of Canada fleabane at sites S1, S2, and S4, which is similar to the 90% control observed by Keeling et al (1989) with 2,4-D ester plus glyphosate (500'300 g a.e. ha (1 ), but only 78% control at sites S3 and S6.…”

Efficacy of 2,4-D Choline/Glyphosate Dimethylamine on Glyphosate Resistant Canada Fleabane (<i>Conyza canadensis</i>) at Different Sizes

“…Overall, at 21 DAA, a higher rate was required to control the larger Canada fleabane. These results are similar to Keeling et al [17], who determined that higher rates of 2,4-D ester were needed to control larger Canada fleabane plants. At 35 DAA, similar rates of 2,4-D choline/glyphosate DMA provided 50%, 80% and 95% control of the three sizes (10, , respectively, where the 10 cm tall Canada fleabane needed a lower rate of 143 g•ae•ha −1 to provide 50% control (Tables 3-5).…”

“…However, Kruger et al [16] found that 2,4-D amine applied to Canada fleabane over 30 cm in height provided 81% control. Keeling et al [17] found that 2,4-D ester (600 g•ae•ha −1 ) provided 97% and 50% -60% control of rosette sized (less than 10 cm) and 10 -15 cm tall Canada fleabane, respectively. These studies show variable control of Canada fleabane with 2,4-D ester and amine.…”

Glyphosate-resistant Canada fleabane [Conyza canadensis (L). Cronq.]: Dose response to glyphosate and control with postemergence herbicides in soybean in Ontario

“…Possible reasons for poor control may include weed size at the time of herbicide application or the interference of a well-developed soybean canopy prior to fleabane bolting, which reduces herbicide contact with the weed (Stougaard et al 1984). Keeling et al (1989) found that while Canada fleabane was controlled by various herbicides at the rosette stage, higher doses were required for plants greater than 10 cm in height. Moseley and Hagood (1990) similarly found that herbicides were more effective when applied early, and that weeds greater than 30 cm were difficult to control.…”