|Richard Jr, Edward|
Submitted to: Proceedings of Southern Weed Science Society
Publication Type: Abstract Only
Publication Acceptance Date: January 20, 2006
Publication Date: June 1, 2006
Citation: Dalley, C.D., Richard Jr., E.P. 2006. Efficacy of tank-mix combinations of asulam and trifloxysulfuron on rhizome johnsongrass control in sugarcane. Proceedings of Southern Weed Science Society. 59:61. Technical Abstract: Perennial johnsongrass is a major weed problem for sugarcane growers in Louisiana. For many years the herbicide asulam has been the only herbicide recommended for selective control of rhizome johnsongrass in Louisiana sugarcane. Some activity on johnsongrass has been observed following postemergence applications of the newly registered herbicide, trifloxysulfuron. Experiments were conducted to evaluate the efficacy of postemergence applications of trifloxysulfuron in combination with asulam on johnsongrass control. Potted johnsongrass plants that had matured to the point of producing rhizomes, were treated in spring 2005, with asulam applied at 0.45 and 0.9 kg ai/ha with and without trifloxysulfuron at 8 g ai/ha). After application, johnsongrass plants were subjected to simulated rainfall (3.8 cm in 15 min) at 1, 3, 6, and 24 hours after treatment (HAT), or to no simulated rainfall. Johnsongrass heights were measured at 2, 4 and 8 weeks after treatment (WAT). Destructive measurements of root, shoot, and rhizome weights and rhizome length were taken at 4 and 8 WAT. Trifloxysulfuron alone reduced whole plant dry weight by 18% at 8 WAT, while asulam applied alone at 0.45 kg/ha reduced johnsongrass biomass by 35%. Combinations of asulam and trifloxysulfuron reduced biomass 54%. Asulam applied at 0.9 kg/ha reduced johnsongrass biomass by 57% and by 80% when combined with trifloxysulfuron at 8 WAT. These results suggest an additive effect on johnsongrass control. Trifloxysulfuron did not improve rainfastness of asulam, and a rainfree period of 24 hours or more was required to elicit maximum response of johnsongrass to asulam, while only 3 hours was required for trifloxysulfuron. In 2003, 2004, and 2005 field studies were conducted to evaluate johnsongrass control in heavily infested sugarcane fields at the USDA-ARS Ardoyne Farm in Schriever, LA. In 2003 and 2004 asulam was applied (0, 0.9, 1.8, and 2.5 kg/ai ha) with and without trifloxysulfuron (0 and 16 g ai/ha) with a standard rate of asulam (3.7 kg/ha) included for comparison. In 2005, asulam was applied at 0, 1.8, 2.5, and 3.7 kg/ha) with and without trifloxysulfuron (0 and 16 g/ha) along with sequential applications of asulam (2.5 followed by 2.5 kg/ha) and asulam (2.5 kg/ha) followed by asulam plus trifloxysulfuron (1.8 kg/ha plus 16 g/ha). Plots were evaluated for johnsongrass control and sugarcane yield. Addition of trifloxysulfuron increased johnsongrass control in 2004 and 2005 but not in 2003. Adding trifloxysulfuron to asulam applications increased yield in one of three years. In 2005, sequential applications of asulam provided the highest levels of johnsongrass control and resulted in the highest yield. Sequential applications of asulam followed by asulam plus trifloxysulfuron provided equal control but lower sugarcane yield compared to the sequential asulam applications. When averaged across asulam rate, trifloxysulfuron increased johnsongrass control by 16% and increased sugar yield by 14%. The combination of asulam and trifloxysulfuron would be most beneficial when only a single application is being planned in fields heavily infested with johnsongrass.