In‐Situ Dissipation of Benomyl, Carbofuran, Thiobencarb, and Triclopyr at Three Soil Depths

Abstract

AbstractData are lacking concerning the persistence of pesticides used in Arkansas rice production. Studies were conducted to examine the dissipation characteristics in field studies of four commonly used pesticides. Crowley silt loam soil (fine, montmorillonitic thermic Typic Albaqualfs) from 2, 20, or 60 cm was treated with benomyl (methyl‐1‐(butylcarbamoyl)‐2‐benzimidazole‐2‐yl carbamate), carbofuran (2,3‐dihydro‐2,2‐dimethylbenzofuran‐7‐yl methylcarbamate), thiobencarb (S‐[(4‐chlorophenyl)methyl]diethylcarbamothioate), or triclopyr ([(3,5,6‐trichloro‐2‐pyridinyl)oxy]acetic acid), and buried in leaching or degradation containers for 0, 34, 104, 184, 280, 371, 736, or 1066 d at Stuttgart, AR. Degradation of carbofuran, thiobencarb, and triclopyr was more rapid than the benomyl metabolite MBC (methyl‐2‐benzimidazole carbamate) with the time for 50% of the initial dose to dissipate (DT50) being 94 d or less. The carbofuran metabolite 3‐keto carbofuran (2,3‐dihydro‐2,2‐dimethyl‐3‐keto‐benzofuranyl‐N‐methyl carbamate) was not detected during this time period. Trace levels of 3‐hydroxy carbofuran (2,3‐dihydro‐2,2‐dimethyl‐3‐hydroxy‐benzofuranyl‐N‐methyl carbamate) were detected periodically. The benomyl metabolite MBC was the most persistent pesticide in this study with DT50 values of 179 to 1020 d. The rates of dissipation decreased with increasing soil depth for all pesticides.