DEGRADATION OF 2,4-D AND FLUOMETURON IN COVER CROP RESIDUES

Degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) was studied in h airy vetch (Vicia villosa Roth) and rye (Secale cereale L.) residues. Transformation of fluometuron ethyl-3-(alpha,alpha,alpha-trifluoro-m-t olyl)urea) was also evaluated in annual ryegrass (Lolium multiforum La n.) residues. Microflora associated with herbicide-desiccated hairy ve tch and rye residues were 100-fold or greater than soils. Microbial ac tivity (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 C-14-carboxyl-labelled 2,4-D and 48 to 60% versus 5 to 17% of C-14-ring-labelled 2,4-D were mineralized in so il and crop residues, respectively. Fluometuron can be degraded by N-d emethylation in ryegrass residues at rates similar to soil however, hi gh moisture content was required. Degradation of herbicides in cover c rop residues was most likely due to limited bioavailability rather tha n biological activity. (C) 1998 Elsevier Science Ltd. All rights reser ved.