Effect of Environment on Wild Oat (Avena fatua) Control with Imazamethabenz or Fenoxaprop Tank-Mixed with Additives or MCPA

Greenhouse and growth chamber experiments were conducted to determine the effect of soil moisture and temperature on the phytotoxicity in wild oat of imazamethabenz or fenoxaprop tank-mixed with certain additives or MCPA. The surfactants Agral 90 at 0.5% and Enhance at 0.5% increased imazamethabenz phytotoxicity under both moist and drought conditions. These surfactants had no significant effect on fenoxaprop phytotoxicity regardless of the soil moisture regimes. Fenoxaprop activity was increased by ammonium sulfate (NH₄)₂SO₄] at 1% but only under well watered conditions. Wild oat control with imazamethabenz was also slightly enhanced in a well watered regime by the addition of sodium bisulfate (NaHSO₄) at 0.13%. At high temperature (30/20°C) and low temperature (10/5°C), the phytotoxicity of imazamethabenz was increased when tank-mixed with Agral 90 at 0.25% or NaHSO₄ at 0.13% compared with that when imazamethabenz was applied alone, if soil moisture was adequate. There was no such increase under conditions of drought and high temperature. (NH₄)₂SO₄ at 1% did not significantly affect imazamethabenz performance irrespective of temperature/soil moisture conditions. The phytotoxicity to wild oat of imazamethabenz or fenoxaprop was not changed by tank-mixing with MCPA isooctyl ester at 300 g a.i./ha, regardless of soil moisture levels. The reduced fenoxaprop phytotoxicity in wild oat due to moisture stress was not readily alleviated by the inclusion of selected additives or MCPA in the tank mixture. Received May 10, 1996; accepted January 10, 1997