Soil factors that may affect activity of the propynyl ester of CGA-82725 {2-[(3,5-dichloro-2-pyridinyl) oxy] phenoxy] propanic acid}, methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, and butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} were examined. Adsorption of the three herbicides on three Illinois soils was similar but very low. Linear partion coefficients (Kd) ranged from 0 to 1.75 for CGA-82725 and haloxyfop, while no adsorption was detected for fluazifop on Drummer silty clay loam, Cisne silt loam, or Bloomfield sand. Conversion to the parent acid (active form) following application to the soil was rapid. The acid form was predominant for 2 months. Two metabolites were recovered; one was common to all three herbicides and intermediate in polarity to the acid and ester forms, and the other, unique to CGA-82725, was slightly more polar than the acid form. Extractability of the herbicides decreased dramatically over time. Haloxyfop and CGA-82725 leached to similar depths in soil column studies. Fluazifop tended to move more readily in the silty clay loam but less rapidly in the sand. Adsorption studies with 15 additional soil or sediment samples with widely varying physiochemical properties yielded adsorption (Kd) values of 0.79, 1.09, and 1.15 for fluazifop, haloxyfop, and CGA-82725, respectively, when averaged over all samples studied. Adsorption did not appear to be significantly influenced by organic carbon content, clay content, or pH.

The widespread evolution of resistance in rigid ryegrass populations to the highly effective, in-crop, selective herbicides used within southern Australian grain-crop production systems has severely diminished the available herbicide resource. A new PRE grass-selective herbicide, pyroxasulfone, may offer Australian grain producers a new option for rigid ryegrass control in wheat crops. The efficacy and level of selectivity of rigid ryegrass control with pyroxasulfone was investigated for a range of annual crop species in potted-plant, dose–response studies. In comparison with other currently available PRE herbicides, pyroxasulfone provided effective control of both resistant and susceptible rigid ryegrass populations. Additionally, control of these populations was achieved at rates that had little or no effect on the growth and survival of wheat. This crop was also the most tolerant of cereal species, with triticale, barley, and oat being more injured at higher pyroxasulfone rates than wheat was. In general though, pulse-crop species were found to be more tolerant of high pyroxasulfone rates than cereal-crop species. There were subtle effects of soil type on the efficacy of pyroxasulfone, where higher rates were required to achieve effective control on soils with higher clay or organic matter contents. The ability of pyroxasulfone to selectively control resistant and susceptible rigid ryegrass populations as identified in these studies clearly indicate the potential for widespread use and success of this herbicide in Australian cropping systems.