Surveys were conducted across the northern Great Plains of Canada in 1996 and 1997 to determine the nature and occurrence of herbicide-resistant (HR) biotypes of wild oat (Avena fatua). The surveys indicated that resistance to acetyl-CoA carboxylase (ACCase) inhibitors (Group 1) occurred most frequently relative to other herbicide groups. Group 1-HR wild oat occurred in over one-half of fields surveyed in each of the three prairie provinces. Of particular concern was the relatively high incidence of multiple-group resistance in wild oat in Saskatchewan and Manitoba. In Saskatchewan, 18% of Group 1-HR populations were also resistant to acetolactate synthase inhibitors (imidazolinones), even though these herbicides were not frequently used. In Manitoba, 27% of fields surveyed had wild oat resistant to herbicides from more than one group. Four populations were resistant to all herbicides registered for use in wheat (Triticum aestivum). Depending on the nature of resistance in wild oat, alternative herbicides available for their control may substantially increase costs to the grower. The cost to growers of managing HR wild oat in Saskatchewan and Manitoba using alternative herbicides is estimated at over $4 million annually. For some HR biotypes, alternative herbicides either are not available or all have the same site of action, which restricts crop or herbicide rotation options and threatens the future sustainability of small-grain annual cropping systems where these infestations occur.

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Field and producer survey of ACCase resistant wild oat in Manitoba. Can. J. Plant Sci. 77: 709-715. In a previous study, 729 townships in Manitoba were differentiated as being at low, medium, or high risk of evolving wild oat resistant to Group 1 herbicides based on herbicide use histories from 1981 to 1993. In the present study, 16 townships representing the three risk categories were surveyed in 1994 in order to determine the percentage of resistant wild oat patches. As well, a questionnaire was mailed to farmers in these townships requesting information on practices and attitudes relating to herbicide resistance. The wild oat survey consisted of sampling seed from conspicuous wild oat patches visible from north-south roads in each township. A total of 533 samples were collected and screened with fenoxaprop-P and sethoxydim using a bioassay. An average of eight resistant wild oat patches was found in the high risk townships. This was significantly higher than in low and medium risk townships where an average of less than one resistant wild oat patch per township was detected. The attitude of producers towards herbicide resistance was similar in all risk categories. However, the number of respondents suspecting Group 1 resistance on their farms was related to risk categories with producers in high risk areas suspecting the most cases of resistance. Bourgeois, L., Morrison, I. N. et Kelner, D. 1997. Inventaire de la folle avoine résistante et sondage auprès d'agriculteurs au Manitoba. Can. J. Plant Sci. 77: 709-715. Dans une étude préalable, on avait utilisé les antécédents d'utilisation des herbicides pour déterminer le degré de risque (faible, moyen ou élevé) de résistance de la folle avoine aux herbicides du Groupe 1 pour 729 townships au Manitoba de 1981 à 1993. Dans la présente étude, on a effectué l'inventaire de 16 townships en 1994, représentant les trois catégories de risque, afin de déterminer le nombre de regroupements denses de folle avoine résistante. De plus, on a envoyé un sondage par la poste aux agriculteurs vivant dans ces townships en vue de recueillir des renseignements concernant leur attitude vis-à-vis de la résistance aux herbicides. Pour effectuer l'inventaire, il fallait récolter des graines à partir de regroupements denses de folle avoine visibles depuis les chemins nord-sud de chaque township. Un total de 533 échantillons ont été récoltés et testés pour la résistance au fénoxaprop-p et au séthoxydime au moyen d'essais biologiques. En moyenne, on a découvert 8 regroupements de folle avoine résistante dans les townships à risque élevé de résistance. Ce résultat est considérablement plus élevé que dans les townships à risques faible et moyen où, en moyenne, on a identifié moins d'un regroupement de folle avoine résistante par township. L'attitude des agriculteurs concernant la résistance aux herbicides était la même, peu importe la catégorie de risque. Toutefois, le nombre d'agriculteurs interrogés qui soupçonnaient de la résistance aux herbicides du Groupe 1 était lié aux catégories de r...

. Nitrogen fixation and growth of one-year stands of nondormant alfaHa in Manitoba.Can. J. Plant

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