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).
