Effect of Ammonium Sulfate and Surfactants on Activity of the Herbicide Sethoxydim

Abstract

The effect of adjuvants including ammonium sulfate and non-ionic surfactants, each at 0.5% of total spray, on sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)-propyl]-3-hydroxy-2-cyclohexen-1-one} (0.1kg/ha) for controlling wild oat seedlings was examined. Addition of both ammonium sulfate and surfactant (Atplus 411F or Citowett Plus) to sethoxydim gave better control than each one added separately. Of five ammonium and six sulfate ions at 0.04M added to the spray solution, ammonium sulfate with a surfactant gave the best wild oat control by sethoxydim. It was also more effective than ammonium thiocyanate at equivalent concentrations (0.005 to 0.04M). Acidic solutions (pH 4.0 and 6.0) of sethoxydim tended to increase the efficiency of wild oat control compared to slightly alkaline solutions (pH 8.0). However, this pH effect on the activity of sethoxydim disappeared when both ammonium sulfate and Atplus 411F surfactant at 0.5% were added to the herbicide solution. There was a noticeable interaction of ammonium sulfate and sethoxydim on wild oat control. Without addition of Renex-36, ammonium sulfate at high concentrations (0.5 to 2.5%) reduced wild oat control by sethoxydim (0.1kg/ha). When the concentrations of Renex-36 increased from 0.1 to 2.5%, the antagonistic effect of ammonium sulfate on sethoxydim was reduced. Overall, the combination of 0.5% ammonium sulfate and 0.5% Renex-36 with sethoxydim at 0.1kg/ha gave the maximum wild oat control. Increased permeability of corn leaf discs may be associated with increased activity of sethoxydim in the presence of adjuvants. Deposit of epicuticular wax on wild oat leaves was altered when either ammonium sulfate, Atplus 411F or the combination was applied with sethoxydim.