Control of rhizome johnsongrass (sorghum halepense) in sugarcane with trifloxysulfuron and asulam

Authors: Dalley, Caleb; Richard Jr, Edward

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2008
Publication Date: 1/1/2008
Citation: Dalley, C.D., Richard Jr, E.P. 2008. Control of rhizome johnsongrass (sorghum halepense)in sugarcane with trifloxysulfuron and asulam. Weed Technology. 22:397-401.

Interpretive Summary: Perennial johnsongrass is a problematic weed for sugarcane growers in Louisiana. Research was conducted to evaluate tank-mixes of the herbicides asulam and trifloxysulfuron on the control of perennial johnsongrass in potted and field trials. In the potted johnsongrass studies it was shown that while trifloxysulfuron applied alone at 8 g/ha reduced johnsongrass height at 2, 4, and 8 weeks after treatment (WAT) it did not reduce biomass accumulation compared with non-treated johnsongrass at 4 WAT and reduced biomass by only 18% at 8 WAT. Asulam applied alone at 460 and 920 g/ha reduced johnsongrass height at 4 and 8 WAT and biomass at both 4 (33 and 38% reduction, respectively) and 8 WAT (27 and 57% reduction, respectively). The addition of trifloxysulfuron (8 g/ha) to asulam applied at 460 and 920 g/ha further reduced johnsongrass height and biomass at 8 WAT (57 and 80% reduction, respectively) compared to asulam applied alone at similar rates. In field studies, trifloxysulfuron applied at 16 g/ha controlled johnsongrass 42% at 5 WAT, but control decreased to 19% at 10 WAT and did not increase sugar yield compared to when no herbicide was applied. Asulam applied alone at 1800, 2700, and 3700 g/ha controlled johnsongrass 63, 70, and 73%, respectively at 5 WAT with control decreasing to 33, 45, and 53%, respectively, at 10 WAT. When trifloxysulfuron (16 g/ha) was added to asulam applications (1800, 2700, and 3700 g/ha) johnsongrass control increased at 5 WAT to 70, 75, and 79%, respectively, compared to asulam alone and at 10 WAT control was 58, 59, and 56%, respectively, with significant increases in control only at the lower asulam rates (1800 and 2700 g/ha). Sugar yield increased from 2080 kg/ha when no herbicide was applied to 4820, 5800, and 6140 kg/ha, respectively, when asulam was applied at 1800, 2700, and 3700 g/ha. Adding trifloxysulfuron to asulam applications significantly increased yields only at the 1800 g/ha asulam rate, where sugar yield increased to 5660 kg/ha. Averaged across all rates of asulam, adding trifloxysulfuron increased sugar yield by 16%. When asulam was applied at 3700 g/ha with trifloxysulfuron sugarcane yielded 6680 kg/ha, a 69% increase compared with no herbicide application. The results of this research indicate that the addition of trifloxysulfuron to asulam applications was beneficial, as improving johnsongrass control resulted in increased sugar yields.

Technical Abstract: Johnsongrass, in its perennial form, is a difficult weed problem for sugarcane growers in Louisiana. Studies were conducted to determine the benefit, if any, of the addition of trifloxysulfuron to postemergence (POST) applications of asulam for the selective control of johnsongrass in sugarcane. Asulam (460 and 920 g ai/ha) was applied with and without trifloxysulfuron (8 g ai/ha) and was compared to trifloxysulfuron (8 g/ha) alone and a non-treated control. Johnsongrass height in a potted experiment, was significantly less at 4 weeks after treatment (WAT) with combinations of asulam (460 and 920 g/ha) and trifloxysulfuron (8 g/ha) than asulam alone. At 8 WAT johnsongrass height was significantly reduced at the higher rate, but not at the lower rate. Trifloxysulfuron alone did not significantly reduce johnsongrass whole plant dry biomass (shoots, roots, and rhizomes) at 4 WAT compared to the control. All other treatments significantly reduced johnsongrass biomass (33-47%). At 8 WAT, all treatments reduced johnsongrass whole plant biomass as compared to the non-treated control. Trifloxysulfuron combined with asulam (460 and 920 g/ha) reduced biomass by 57 and 80%, respectively, while asulam alone reduced biomass by 27 and 57%, respectively, and trifloxysulfuron alone reduced biomass by 18%. In a field study, adding trifloxysulfuron at 16 g/ha to asulam at 1,800; 2,700; and 3,700 g/ha significantly increased visual control ratings of rhizome johnsongrass at all rates for 5 and 8 WAT and at the two lower rates 10 WAT. Sugarcane yield was not improved when trifloxysulfuron was applied alone but increased with increasing rates of asulam. Within asulam rates of application, the addition of trifloxysulfuron significantly increased sugarcane yield (17%) only at the lowest asulam rate (1,800g/ha), but when averaged across asulam rates there was a 14% increase in sugar yields when trifloxysulfuron was included.