Studies on the Timing of Application, Soil Activity, and Factors Affecting Soil Activity of Several Selective Grass Herbicides (Sethoxydim, Fluazifop-Butyl, Haloxyfop-Methyl)

169 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.Field studies on the management of postemergence grass herbicides were conducted. No reduction in soybean yield occurred as a result of up to 5 weeks of early grass competition. Delayed treatment of sethoxydim (10-15 cm stage) especially when planting early provided the best grass control by allowing for maximum foxtail germination. Results indicated potential benefit resulting from residual activity following postemergence treatment when treating early, particularly when planting soybeans early.Field studies evaluating soil activity following preemergence and postemergence application of several of the selective grass herbicides were conducted. All herbicides tested demonstrated soil activity showing an order of toxicity on a Catlin silt loam soil of CGA-82725 > haloxyfop-methyl > fluazifop-butyl at suggested postemergence use rates or double. Acceptable preemergence control without soybean yield reduction appeared possible at postemergence use rates combined with canopy closure and/or cultivation or by increased application rates. Residual activity following postemergence application would supplement the postemergence control activity and be of particular importance under conditions of prolonged grass germination.Sorption studies indicated similar but low soil adsorption for the selective grass herbicides. K(,d) values were 1.15, 1.09 and 0.79 for CGA-82725, haloxyfop-methyl and fluazifop-butyl, respectively. Sorption constants normalized for soil organic carbon content indicate a moderate to high potential for mobility. Adsorption was not influenced by soil organic carbon content or clay content. Sorption tended to decrease as soil pH increased.Conversion to the acid form following application to the soil was rapid. The acid, the active form, remained the predominant form throughout the two month period covered by the experiment. A common metabolite to all the herbicides was intermediate in polarity to the acid and ester forms. A predominant metabolite slightly more polar than the acid form was unique to CGA-82725. Extractability of the herbicides declined dramatically over time. Degradation of the herbicides and decline in extractability were both slower at lower temperatures.Leaching results indicated similar movement for haloxyfop-methyl and CGA-82725. Fluazifop-butyl tended to move more readily in the heavier soil, but less rapidly in the sandy soil. Movement was not extensive for any of the herbicides under low rainfall condition, however, as rainfall intensity increased soil activity was significantly diminished.U of I OnlyRestricted to the U of I community indefinitely during batch ingest of legacy ETD