Influence of Prior Pesticide Treatments on EPTC and Butylate Degradation

Field and laboratory studies were conducted to examine the influence of previous pesticide use, number of prior EPTC (S-ethyl dipropyl carbamothioate) and butylate [S-ethyl bis(2-methylpropyl)carbamothioate] applications, and pretreatment of soil with EPTC and butylate metabolites on EPTC and butylate degradation. EPTC degradation was enhanced in Clay Center and Scottsbluff soils following three annual EPTC, butylate, or vernolate (S-propyl dipropylcarbamothioate) applications, but was not affected in soils following three annual atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile}, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], or cycloate (S-ethyl cyclohexylethylcarbamothioate) applications. EPTC degradation rate was not affected in a Scottsbluff soil following three annual carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) applications, but was partially enhanced in a Clay Center soil. Self- and cross-enhanced degradation of EPTC and butylate did not change regardless of the number of prior annual applications of each herbicide. The degradation rates of EPTC and butylate were not affected by soil pretreated with butylate sulfone, but the degradation rates-were fully enhanced by pretreatment with the respective sulfoxides of each herbicide. In cross-enhancement testing, EPTC and butylate degradation was partially enhanced in Clay Center soil pretreated with the sulfoxides of each.