ENHANCED SOIL MICROBIAL-DEGRADATION OF CARBOFURAN AND FENSULFOTHION - A FACTOR CONTRIBUTING TO THE DECLINE IN EFFECTIVENESS OF SOME SOIL INSECT CONTROL PROGRAMS IN CANADA

Compilation of field efficacy data accumulated over a number of years indicated that cabbage maggot (CM) radicum (L) control by carbofuran and fensulfothion in Newfoundland has declined with time. A similar trend was apparent in Ontario with carbofuran used to control carrot rust fly (CRF), Psila rosae (F) and carrot weevil (CW). Laboratory tests conducted between 1982 and 1985 with two Newfoundland CM strains and an Ontario CRF strain indicated that declining efficacy could not be attributed to development of insect resistance to recommended insecticides. Other tests indicated that the two Newfoundland soils developed the capacity for rapid degradation of carbofuran or fensulfothion in a single growing season. In an organic soil used for carrot production in Ontario, anti-carbofuran activity was apparent within 1 week after application of granular carbofuran in the seed furrow and was high after 3 weeks. The data suggest that development in soil of microbial populations capable of enhanced degradation of carbofuran or fensulfothion is contributing to the erratic performance of these insecticides in CM, CRF, CW and other root maggot control programs in Canada.