Spray carrier stability, plant mobility, and runoff potential of trifloxysulfuron

Triflxysulfuron is a sulfonylurea herbicide developed for postemergence weed control in cotton, sugarcane, and turf. Greenhouse and laboratory studies were conducted at the Texas A&M University campus and at the USDA-ARS research facility in Stoneville, MS to: 1) quantify the dissipation of trifloxysulfuron in a spray tank at 0, 1, 3, 7, 14, and 21 d after mixing as influenced by pH of the spray carrier and evaluate the resulting effects on efficacy on Palmer amaranth (Amaranthus palmeri S. Wats); 2) determine the effect of spray carrier pH on absorption and translocation of radiolabeled trifloxysulfuron in Palmer amaranth and Texasweed (Caperonia palustris (L.) St. Hil.); 3) determine average edge-of-field concentrations, total mass losses, and fractional losses of trifloxysulfuron applied to cotton at the 5-leaf stage and to bare soil as influenced by simulated rainfall. The dissipation of trifloxysulfuron followed first-order kinetics. Calculated half-life values indicated that hydrolysis occurred more rapidly with the more acidic spray carriers with little or no difference between neutral and alkaline pH levels. Bioassay on Palmer amaranth showed no differences in plant dry weights due to pH level or dissipation time. The absorption of 14C-trifloxysulfuron was greater for Palmer amaranth than for Texasweed when averaged over time and pH. Altering pH did not affect the translocation of trifloxysulfuron in Palmer amaranth. In contrast, translocation of 14C-trifloxysulfuron in Texasweed increased in the order of pH 5 < pH 7 = pH 9. Cumulative trifloxysulfuron losses in runoff from cotton plots were 0.21 g ha-1 while losses from bare plots were 0.13 g ha-1. These values corresponded to fractional losses of 2.7% for cotton plots and 1.7% for bare plots of the total amount applied. These studies provide important information regarding the stability, plant uptake, and runoff potential of a commonly used sulfonylurea herbicide.