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THE INFLUENCE OF TEMPERATURE, MOISTURE, PRIOR APPLICATION, AND HERBICIDE EXTENDERS ON THE DEGRADATION OF THIOCARBAMATE HERBICIDES
Abstract
Field and laboratory studies were conducted during 1980 through 1982 designed to examine the influence of temperature, moisture, prior application, and herbicide extenders on the degradation of thiocarbamate herbicides in soil. In the field, previous successive annual application of EPTC (S-ethyl dipropylthiocarbamate) appear to have enriched the soil resulting in a rapidly accelerated rate of microbial degradation of EPTC. Only one application of EPTC was necessary to induce rapid EPTC degradation 12 months later. While butylate (S-ethyl diisobutylthiocarbamate) degradation was increased on EPTC-enriched soils, butylate degradation rates were not as rapid as those observed for EPTC. Addition of R-33865 (O,O-diethyl-O-phenol phosphorothioate) to butylate or EPTC (formulated at a 6:1 ratio w/w) extended herbicide persistence in field soils with and without prior EPTC application. Laboratory studies revealed that temperatures below 15 C and specifically 5 C extended EPTC persistence in EPTC-enriched soils, and slightly increased EPTC persistence in soils with no prior thiocarbamate application. EPTC degraded most rapidly at 25 C in all soils. The rate of breakdown of ('14)C-carbonyl EPTC to ('14)CO(,2) in EPTC-enriched soils was dependent on soil moisture from below 3% and independent of moisture above 3%. While evolution of ('14)CO(,2) from ('14)C-carbonyl-EPTC in enriched soils was significantly reduced when R-33865 was added, the initial lag period of EPTC degradation was not restored. Although the rate of microbial degradation of butylate was increased on an EPTC-enriched soil collected from the field and treated in the laboratory, it was not rapid as the accelerated breakdown rate observed for EPTC and vernolate (S-propyl dipropylthiocarbamate). Addition of R-33865 to butylate, EPTC, and vernolate inhibited their microbial breakdown and extended thiocarbamate persistence on an EPTC-enriched soil. Laboratory research showed a maximum rate of EPTC degradation resulted after only one prior application with temperature and moisture held constant. Butylate degradation increased with subsequent butylate applications; however, the rate of butylate degradation was never as rapid as that observed for EPTC on EPTC-enriched soil.
Subject Area
Agronomy
Recommended Citation
OBRIGAWITCH, TIMOTHY TOBIAS, "THE INFLUENCE OF TEMPERATURE, MOISTURE, PRIOR APPLICATION, AND HERBICIDE EXTENDERS ON THE DEGRADATION OF THIOCARBAMATE HERBICIDES" (1982). ETD collection for University of Nebraska-Lincoln. AAI8217552.
https://digitalcommons.unl.edu/dissertations/AAI8217552