Laboratory studies were conducted to investigate the processes of imazaquin and imazethapyr degradation in soil. Microbial degradation of 14C-imazaquin and 14C-imazethapyr was monitored by measuring 14CO2 evolution compared to nonsterile soil. 14CO2 evolution was greatest from carboxyl-labeled imazaquin and imazethapyr compared to ring-labeled imazaquin and imazethapyr. A corn root bioassay indicated nearly complete loss of herbicidal activity in nonsterile soil after 5 mo, but herbicide activity was reduced only 14% in sterile soil. 14CO2 evolution more than doubled when soil temperature increased from 15 to 30 C. Total CO2 production responded similarly. Degradation of imazaquin and imazethapyr increased as soil moisture increased from 15% (-2.4 MPa) to 75% of field capacity (-0.03 MPa).

Microbial degradation of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} was monitored by measuring 14CO2 evolution for 7 months under controlled laboratory conditions. Up to 10% of the 14C chain-labeled imazaquin that was applied to a Crowley silt loam was evolved as 14CO2 in 7 months. Less evolution of 14CO2 occurred on a Sharkey silty clay, a soil with higher clay and organic matter content, than on silt loam soils. The loss of 66 to 100% of the imazaquin applied to a Crowley silt loam incubated for 8 months at 18 C or 35 C, respectively, suggested that metabolic changes in addition to CO2 evolution were occurring. Rapid loss of imazaquin phytotoxicity occurred when soils were held at warm-moist (35 C and −33 kPa) conditions conducive to microbial growth. Imazaquin was more persistent in soils stored under cool, dry (18 C and −100 kPa) conditions. Imazaquin on a soil surface dissipated rapidly when exposed to ultraviolet light or sunlight. Photodecomposition could be a major mode of imazaquin dissipation if this herbicide is allowed to remain on the soil surface.