Degradation of 2,4-D and fluometuron in cover crop residues

Degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) was studied in hairy vetch (Vicia villosa Roth) and rye (Secale cereale L.) residues. Transformation of fluometuron (1,1-dimethyl-3(α,α,α-trifluoro-m-tolyl)urea) was also evaluated in annual ryegrass (Lolium multiforum Lam.) residues. Mcroflora associated with herbicide-desiccated hairy vetch and rye residues were 100-fold or greater than soils. Microbial activity (fluorescein diacetate hydrolysis and respiration) were 6-fold or greater in hairy vetch and rye residues than soil. In 14-d studies, 78 to 82% versus 28 to 40% of 14C-carboxyl-labelled 2,4-D and 48 to 60% versus 5 to 17% of 14C-ring-labelled 2,4-D were mineralized in soil and crop residues, respectively. Fluometuron can be degraded by N-demethylation in ryegrass residues at rates similar to soil, however, high moisture content was required. Degradation of herbicides in cover crop residues was most likely due to limited bioavailability rather than biological activity.