Failure of the herbicide carbetamide to adequately control annual grasses upon repeat-ed annual application was linked to rapid degradation of this herbicide in soil. Rapid carbetamide degradation in soil was clearly evident following application at normal field rates and when evaluated at time intervals reflecting normal agronomic use. The DT50 Of carbetamide in soil was reduced from 54 to 9 days when evaluated one year after a single carbetamide application to previously untreated soil. Rapid carbetamide degradation was transferred to previously untreated soil by addition of 1% rapid carbetamide adapted soil and was inhibited following pre-treatment with the broad-spectrum antibiotic chloramphenicol. In carbetamide-adapted soil mineralisation of [C-14-ring] labelled carbetamide to (CO2)-C-14 occurred at a faster rate than with previously untreated soil. It was concluded that rapid carbetamide degradation upon repeated application is probably linked to the adaptation of soil bacteria which can utilise carbetamide as a source of carbon and energy. (C) 2001 Elsevier Science Ltd. All rights reserved.