The purpose of this study was to determine cross-resistance patterns among wild oat lines resistant to acetyl-CoA carboxylase (ACCase) inhibitors and to determine which, if any, cross-resistant type was more common than another. Discriminatory concentrations of two aryloxyphenoxy-propionates (APP) and three cyclohexanediones (CHD) were determined using a petri-dish bioassay. These concentrations were then applied to 82 resistant wild oat lines identified in previous studies. In addition, two resistant standards (UM1 and UM33) and a susceptible standard (UM5) were included in the experiments. Coleoptile lengths expressed as percentages of untreated controls were used to assess the level of resistance to each herbicide. Large variations were observed among wild oat lines and herbicides. However, cluster analysis summarized the relationship between the five herbicides (variables) and the wild oat lines into three main cross-resistance types. Type A included wild oat lines with high resistance to APP herbicides and no or low resistance to CHD herbicides. Types B and C included those with low to moderate resistant and high levels of resistance to all five herbicides, respectively. Type C was the most common cross-resistance type. Relationships among herbicides were determined using pairwise correlation and principal component analysis (PCA). All correlations were high between APP herbicides and between CHD herbicides but not between APP and CHD herbicides. The first two axes of the PCA accounted for 88.4% of the total variance, with the first axis correlated to the CHD herbicides and the second axis correlated to the APP herbicides. In the PCA, wild oat lines were segregated into the three types identified in the cluster analysis. Although CHD and APP herbicides bind at the same region on the ACCase, resistant wild oat lines respond differently to them.

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...

Bourgeois, L. and Morrison, I. N. 1997. Mapping risk areas for resistance to ACCase inhibitor herbicides in Manitoba. Can. J. Plant Sci. 77: 173-179. Since 1976, seven acetyl coenzyme-A carboxylase (ACCase) inhibitors (referred to as Group 1 herbicides) have been registered in western Canada for wild oat (Avena fatua L.) and green foxtail (Setaria viridis L.) control. In 1990, Group 1 resistant wild oat populations were identified from fields in Manitoba which had been repeatedly sprayed with these products during the previous 10 yr. Since the occurrence of resistance is directly related to the frequency of herbicide use, the purpose of this study was to compile herbicide use histories on a province-wide basis using data included in the Manitoba Crop Insurance Corporation (MCIC) database. The database was used to determine the relative importance of Group 1 herbicide use in major crops compared with other products, and to identify individual townships at low, medium and high risk for developing Group 1 resistance. Low, medium and high risk townships were arbitrarily defined as those in which Group 1 products were used on less than 30%, on 30 to 50% and on more than 50% of the sprayed fields, respectively. From 1981 to 1993, Group 1 herbicide use increased from 15 to 50% of the sprayed area, and since 1990, these products have been used on one out of two sprayed fields on an annual basis, with the most intensive use in flax. In the early 1980s, fewer than 5% of the townships were at high risk. These were located near the towns of Swan River, Dauphin and Treherne, and the city of Winnipeg, which were the locations where Group 1 resistant wild oat and green foxtail were first identified. Between 1989 and 1993, more than 40% of the townships were considered to be at high risk. Should the trend toward increased use of Group 1 herbicides continue through the 1990s, the resistance problem will inevitably worsen. , communément appelés les herbicides du Groupe 1, ont été enregistrés dans l'ouest canadien pour le contrôle de la folle avoine (Avena fatua L.) et de la sétaire verte (Setaria viridis L.). En 1990, on a identifié de la folle avoine résistante aux herbicides du Groupe 1 dans des champs au Manitoba où l'on avait fréquemment utilisé ces produits dans les 10 dernières années. Puisque la résistance est intimement liée à la fréquence d'utilisation des herbicides, le but de la présente étude était de compiler des antécédents d'utilisation des herbicides dans l'ensemble de la province au moyen de données tirées de la base de données de la Direction d'assurance-récolte du Manitoba (MCIC). On a premièrement utilisé la base de données afin de déterminer l'utilisation relative des herbicides du Groupe 1 en grande culture comparativement à d'autres produits. En outre, la base de données a permis d'identifier les townships à faible risque, à risque moyen et à risque élevé de développer de la résistance aux herbicides du Groupe 1. Dans un township à faible risque, moins de 30 % des champs sont traités annuellement avec un h...

Although rotational benefits of non-cereal crops have been observed in small plot research trials few quantitative data are available on a field scale. In this study, field data of farmers from the Manitoba Crop Insurance Corporation were analysed to compare yield of wheat (Triticum aestivum L.) following different crops. The yield of wheat following wheat was used as a basis of comparison among crop sequences. The yield data were collected between 1982 and 1993 from fields 64 ha in size, located throughout the province of Manitoba. During this period, the yield of wheat following flax (Linum usitatissimum L.), peas (Pisum sativum L.), and canola (Brassica napus L.), on average was 16%, 11%, and 8% higher, respectively, than wheat following wheat. In one year, the yield of wheat was increased by as much as 41% following a field pea crop. Key words: Crop rotation, barley, canola, flax, field pea, wheat

. Can. J. Plant Sci. 77: 703-708. A survey was conducted in a township near Treherne, Manitoba to determine the frequency of Group 1 resistant wild oat in 30 randomly selected cereal fields. On average, 61% of the 30 fields were sprayed annually with ACCase inhibitor (Group 1) herbicides from 1983 to 1993. Wild oat were sampled at 80-m intervals on a predefined grid pattern across whole fields. Wild oat densities were recorded and seeds were collected from 0.25 m -2 quadrats. Seeds were also collected from conspicuous wild oat patches occurring outside the spaced quadrats. Plants were determined to be susceptible or resistant to fenoxaprop-P and/or sethoxydim using a seed bioassay procedure. Results from the structured survey indicated that resistant wild oat occurred in nine fields. Densities in quadrats containing resistant wild oat were generally higher than in quadrats with susceptible wild oat. By combining the results of the structured survey with the patch collection, resistance was detected in 20 out of the 30 fields. While resistant weeds generally occurred in small patches, in two of the fields, resistant plants occurred over much larger areas. The evidence suggests that as many as two fields in three may harbour Group 1 resistant wild oat in high risk townships in Manitoba.Key words: Weed survey, resistance assessment, wild oat, ACCase inhibitors Bourgeois, L. et Morrison, I. N. 1997. Inventaire de la folle avoine résistante aux inhibiteurs de l'ACCase dans un township à risque élevé du Manitoba. Can. J. Plant Sci. 77: 703-708. Un inventaire effectué dans un township près de Treherne, au Manitoba, a permis de déterminer la fréquence de folle avoine résistante aux produits du Groupe 1 dans 30 champs sélectionnés au hasard. En moyenne, on avait traité 61 % des 30 champs annuellement avec des herbicides du Groupe 1 entre 1983 et 1993. Des échantillons de folle avoine ont été récoltés à des intervalles de 80 m selon une grille déterminée au préalable sur toute la surface des champs. On a enregistré la densité de la folle avoine et procédé à la collecte de graines à l'intérieur de quadrats de 0,25 m -2 . On a récolté également des échantillons de toutes les talles visibles de folle avoine situées à l'extérieur des quadrats. Au moyen d'un essai biologique, les plantes ont ensuite été évaluées comme susceptibles ou résistantes au fénoxaprop-p et/ou au séthoxy-dime. Les résultats de l'inventaire à intervalles réguliers ont indiqué que neuf champs contenaient de la folle avoine résistante. La densité dans les quadrats où se trouvait de la folle avoine résistante était généralement plus élevée que dans les quadrats contenant de la folle avoine susceptible. La mise en commun des résultats de l'inventaire à intervalles réguliers et de l'échantillonage de talles visibles a signalé la présence de résistance dans 20 des 30 champs. Même si la folle avoine résistante apparaissait le plus souvent en petites talles, on a trouvé de la folle avoine résistante éparpillée dans deux des champs sélectionnés. Les résultats ind...