The degradation of 14C-labeled metolachlor, acetochlor, and pretilachlor in control and soils with 10-yr metolachlor- history or 3-yr butylate history was studied by monitoring the evolution of 14CO2 in soil biometer flasks. The degradation rate of 14C-phenyl-labeled metolachlor was similar in soils with 0- and 10-yr metolachlor history over 52 d. 14C was released from carbonyl-labeled metolachlor about 40% faster than from phenyl-labeled metolachlor in both soils. Soil sterilization by autoclaving reduced significantly the metolachlor degradation rate in both soils. Degradation of 14C-labeled EPTC in soils with 3-yr butylate history was much faster than in soils with no history. Soil sterilization reduced the EPTC degradation rate, confirming microbial degradation. The degradation rates of acetochlor, metolachlor, and pretilachlor were similar in soils with and without butylate history. Most of the 14C that remained in history and nonhistory soils was extractable with ethyl acetate or sodium hydroxide. Three major metabolites of metolachlor and EPTC were detected by thin-layer chromatography (TLC) of extracts from both soils. In contrast to the situation with carbamothioate herbicides, soils exposed repeatedly to metolachlor or other acetanilides are not prone to become adapted to these herbicides. Soils with carbamothioate history did not exhibit any apparent cross-adaptation toward acetanilide herbicides.

The effect of three rates of metolachlor on ‘Prime Time’ and ‘Tastie’, early maturing, fresh-market cabbage was evaluated in two geographically distinct regions of New York in 1986 and 1987. Metolachlor, when applied at 1.1, 1.7, and 2.2 kg ai/ha either pretransplant or 48 h after transplanting, caused no observable negative effects on either cabbage variety in either year when grown on sandy loam soils on Long Island. On a central New York silt loam soil, injury from metolachlor at 1.7 and 2.2 kg/ha applied post-transplant was negligible and transient. Metolachlor applied post-transplant caused a delay in maturity of Tastie cabbage in both years but not Prime Time; however, total yields equalled those of the weed-free controls with both varieties. Metolachlor applied pretransplant frequently caused excessive and persistent injury and often reduced cabbage yields.