Survey of management practices affecting the occurrence of wild oat (Avenafatua) resistance to acetyl-CoA carboxylase inhibitors

A survey conducted across agricultural ecoregions of Saskatchewan in 1996 r evealed that wild oat (Avena fatua) populations resistant to acetyl-CoA car boxylase (ACCase) inhibitors were present in approximately 10% of Saskatche wan fields (2.4 million ha). In the Aspen Parkland and Boreal Transition ec oregions, this increased to 17%. The objective of this study was to determi ne if agronomic practices promoted or delayed resistance and to assess prod ucer awareness of herbicide resistance. Weed resistance and management ques tionnaire data from the 1996 resistance survey and management questionnaire data from the 1995 Saskatchewan weed survey were submitted to multiway fre quency analysis. The frequency of occurrence of herbicide-resistant wild oa t was related directly to ACCase inhibitor use. Resistance to cyclohexanedi one (CHD) herbicides was not related to CHD use but to frequency of ACCase inhibitor use (i.e., CHD + aryloxyphenoxypropanoate [AOPP]), suggesting tha t the pressure imposed by AOPPs contributed to the selection of CHD resista nce in wild oat. ACCase inhibitor use was more extensive in the Aspen Parkl and and Boreal Transition ecoregions than in the Mixed and Moist Mixed Gras sland ecoregions, Crop rotations were not conducive to rotation of herbicid es with different sites of action, Frequency of ACCase inhibitor use increa sed with frequency of annual crops, in spite of the inclusion of cereal and dicot crops in the rotation. Producers utilizing conservation tillage prac tices in the Grassland ecoregions used proportionally more ACCase inhibitor s than those using conventional tillage practices. This increase in ACCase use in conservation tillage systems did not result in an increased incidenc e of wild oat populations resistant to ACCase inhibitors. Producers reporti ng troublesome wild oat populations tended to have proportionally more ACCa se resistant wild oat. Producers who reported practicing weed sanitation we re less likely to have resistant wild oat than those who were less careful. Increased awareness and implementation of management practices that will r educe the dependency on ACCase herbicides are required to better enable pro ducers to prevent, delay, or manage herbicide-resistant wild oat population s.