Laboratory experiments were conducted to evaluate the biodegradation of14C-labeled butylate, cycloate, EPTC, pebulate, and vernolate in three butylate-history soils that had received three to eight applications of butylate under field conditions. After 20 days, biodegradation of butylate and EPTC was accelerated and had no lag phase in all three butylate-history soils. Butylate-adapted microorganisms were cross-adapted for EPTC and degraded EPTC as readily as butylate. Biodegradation of butylate and EPTC in Dothan soil without a butylate history exhibited a lag phase of 6 days after which14CO2was evolved at an exponential rate. This indicated that enhanced biodegradation was induced after one application of butylate or EPTC. Butylate-adapted microorganisms were cross-adapted for vernolate and pebulate in Dothan and pebulate in Wagram soils with a butylate history. Biodegradation of vernolate and pebulate was not enhanced in Varina butylate-history soil. After 20 days, there was no cross-adaptation for cycloate in any soil. These findings indicated that biodegradation of carbamothioates was influenced by soil type and previous carbamothioate use and that caution should be exercised in use of EPTC on fields of previous butylate use.

Laboratory experiments were conducted to evaluate butylate and EPTC degradation in two butylate-history soils collected in 1983, 1984, and 1985, and stored at 4 C. No significant differences in biodegradation of butylate and EPTC were found due to length of cold storage of Varina or Wagram soils. Enhanced biodegradation of butylate and cross-adaptation for EPTC were not affected. Storage of soils up to 2 yr should not adversely affect results.