Evaluation of efficacy, soil behavior and dissipation of herbicides in agronomic crops
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Field, greenhouse and laboratory experiments were conducted to investigate fomesafen soil behavior, degradation, dissipation and cotton tolerance. Fomesafen adsorption to soil was significantly affected by pH and clay content while desorption was correlated to sand, silt, clay fraction, pH and soil organic matter. Fomesafen degradation was minimum in Cecil sandy loam or Tifton loamy sand during a 90 day laboratory incubation. Under field conditions, fomesafen persistence varied significantly between Cecil sandy loam and Tifton loamy sand. The half-life in the respective soils was 47 and 6 d for 280 g ai ha-1; and 34 and 4 day for 560 g ai ha-1. Cotton was not damaged when fomesafen applied preemergence within the 280 to 420 g ai ha-1 registered use rates. However stand count, height and yield may be reduced by fomesafen rates exceeding 1120 g ai ha-1. Herbicide tolerance and efficacy were initiated for Miscanthus × giganteus in laboratory, greenhouse and field, with the objective of screening potential herbicides to control weeds during M. giganteus establishment and eradicating M. giganteus for crop rotation and invasive control. Preemergence herbicide screening in greenhouse experiments indicated M. giganteus rhizomes were tolerant of atrazine, S-metolachlor, mesotrione, pendimethalin, acetochlor and metribuzin. However, experiments that screened preemergence herbicides using M. giganteus fertile seeds indicated seed germination failed completely when treated with dinitroanilines, cellulose synthesis inhibitor, and protoporphyrinogen oxidase inhibitors; germination responses to very long chain fatty acid inhibitors varied from 46 to 94%. In postemergence herbicide screening experiments, nicosulfuron, trifloxysulfuron, sulfometuron, pyrithiobac, clodinafop and fluazifop reduced shoot dry weight of rhizome-established M. giganteus but only sulfometuron and fluazifop affected shoot regrowth from rhizomes. The glyphosate rate to reduce 50% growth compared to nontreated control for Miscanthus shoot dry weight, underground biomass and regrowth shoot dry weight were 702, 1174 and 1637 g ae ha-1 respectively. Single glyphosate application of 1.68 kg ae ha-1 reduced shoot height and dry weight, but did not affect underground biomass and shoot regrowth; two applications were required to eliminate regrowth. Postemergence glyphosate tank mixed with fluazifop, imazapyr, pyrithiobac or sulfometuron improved control efficacy compared to glyphosate alone.