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.
A 3-yr study was conducted in Wheatland County, Alberta to determine if agronomic practices of growers influenced the occurrence of herbicide resistance in wild oat. Wild oat seeds were collected in 33 fields in 1997 and in 31 fields in each of 1998 and 1999 (one field per grower). Seedlings were screened for resistance to two acetyl-CoA carboxylase (ACCase) inhibitors, imazamethabenz, an acetolactate synthase (ALS) inhibitor, and triallate, a thiocarbamate herbicide. A questionnaire on herbicide resistance awareness and management practices was completed by each grower. Both ACCase and ALS inhibitor resistance in wild oat were linked to a lack of crop rotation diversity. In addition, ALS inhibitor–resistant wild oat was associated with conservation-tillage systems and recent use of herbicides with that mode of action. Results of this study suggest that timely tillage and inclusion of fall-seeded and perennial forage crops in rotations will effectively slow the selection of resistance in this grass species.
The pea leaf weevil, Sitona lineatus (Linnaeus) (Coleoptera: Curculionidae), is an important pest of field peas, Pisum sativum Linnaeus (Fabaceae), and faba beans, Vicia faba Linnaeus (Fabaceae), that has recently become established in the Prairie Provinces of Canada. Male pea leaf weevils produce an aggregation pheromone, 4-methyl-3,5-heptanedione, in the spring when overwintered weevils migrate to fields to feed and mate. The current study tests the attractiveness of the aggregation pheromone with and without synthetic bean volatiles to pea leaf weevils in the spring and in the fall when weevils seek perennial legumes to feed and overwinter. Modified Leggett traps similar to those used in Europe did not retain weevils in this study. Aggregation pheromone-baited pitfall traps caught male and female weevils in the spring and fall. Weevils were not attracted to traps baited with three bean volatiles, (Z)-3-hexen-1-yl acetate, (Z)-3-hexen-1-ol, and linalool. Bean volatiles did enhance response to pheromone, but only in the fall. Weevils were captured in most semiochemical-baited traps in a 1:1 sex ratio, but female-biased catch in control traps might indicate greater activity of females in the trap vicinity. This study lays the groundwork for semiochemical-based monitoring to detect pea leaf weevil spread in the Prairie Provinces.
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