Wild oat is the most economically detrimental weed species in the Canadian Prairies and effective herbicidal control options are limited due to widespread resistance to ACCase inhibitors, ALS inhibitors, and lipid biosynthesis inhibitors; therefore, evaluation of new herbicidal modes of action such as pyroxasulfone and sulfentrazone for control is critical. Two wild oat populations (HR08-210 and HR11-151) were first subjected to a discriminating dose screen to characterize resistance to ACCase and ALS inhibiting herbicides in comparison with a susceptible population (S1988). Dose-response experiments with triallate, pyroxasulfone, and sulfentrazone were then conducted to evaluate potential cross-resistance. Screening indicated both herbicide-resistant (HR) populations were resistant to ACCase-and ALS inhibiting herbicides, most likely due to enhanced metabolism and an ACCase mutation. HR08-210 and HR11-151 were resistant to triallate (resistance ratios of 2.53 and 3.39, respectively), but cross-resistance to pyroxasulfone (2.78) and sulfentrazone (2.0) was only observed in HR11-151. Results indicate previously selected resistance to ACCase and ALS inhibitors (enhanced metabolism and ACCase mutation) or triallate (enhanced endogenous gibberellins) could limit the utility of new herbicide modes of action for control of wild oat.

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Wild oat control options are limited in western Canada due to resistance to most common herbicides. Control of wild oat with pyroxasulfone, a soil-applied, very-long-chain fatty-acid inhibitor, was investigated. A series of greenhouse and field experiments were conducted to isolate the effects of vertical seed position, site of herbicide interception, and tillage on wild oat control with pyroxasulfone in comparison with triallate. In greenhouse experiments, wild oat shoot length (soil surface to leaf tip) was reduced (P<0.05) in shallow-seeded wild oat compared with deep-seeded wild oat with pyroxasulfone (6.2 and 9.8 cm, respectively) and triallate (3.7 and 13.2 cm, respectively). Soil-applied pyroxasulfone remained in the top 2.5 cm of the soil with or without a simulated rainfall event. Pyroxasulfone was most effective if either the seed or the shoot 1 cm above the seed intercepted the herbicide layer. If a wild oat emerges from deeper in the soil profile, the sensitive part of the seedling may not intercept an effective rate of pyroxasulfone in the soil. In field experiments comparing deep- and shallow-seeded wild oat treated with pyroxasulfone and triallate in fields with and without tillage, there were no significant effects of tillage alone on wild oat shoot length. Deep-seeded wild oat emerged early, and while herbicides reduced shoot growth, shoots were >10 cm. Shallow-seeded wild oat had delayed emergence, possibly due to reduced soil moisture, and herbicides reduced shoot growth to <10cm. Pyroxasulfone is likely to be more effective in no-till fields where wild oat seeds are not located deep in the soil.

Spotted knapweed is a prohibited noxious weed that is primarily controlled with auxinic herbicides. A population collected from a managed rangeland in East Kootenay, BC, was highly resistant to both clopyralid and picloram, with R/S ratios of >25 600 and 28, respectively. This is the first report of resistance in spotted knapweed. Résumé: La centaurée maculée est une adventice nocive interdite que l'on détruit principalement avec des désherbants à auxine. Un peuplement résistant au clopyralid et au picloram (rapport entre plants résistants et sensibles respectivement supérieur à 25 600 et de 28) a été découvert sur un grand parcours aménagé d'East Kootenay, en Colombie-Britannique. Il s'agit du premier signalement d'une telle résistance chez la centaurée maculée. [Traduit par la Rédaction]

Lodging risk in spring wheat has grown with the introduction of high yielding cultivars that require high nitrogen (N) inputs to optimize grain yield and protein content. Canopy management (CM) strategies have been used to reduce lodging risk. However, the short growing season and unpredictable moisture supply may limit the use of these strategies in the Canadian Prairies. The objective of this study was to quantify the ability of agronomic practices to modify the early season crop canopy, and hence lodging risk, and to determine how these practices influence N use and final grain N yield. Split-plot field trials were established at four site-years in Manitoba to evaluate CM strategies including three plant densities, a split N fertilizer application, and the application of chlormequat chloride (CCC) on canopy size (dry matter and height at anthesis), N uptake and remobilization, lodging and stalk strength, grain yield, protein, and grain N yield on the cultivar AAC Brandon. Precipitation was low during this study (64 – 78% of long-term average) resulting in modest yields and low lodging pressure. However, low plant density, split N, and CCC applications all showed potential to reduce lodging risk without reducing grain yield or protein concentration. Split N and PGR applications increased final grain N yield by 11.2 and 2.4 %, respectively. Therefore, CM practices have potential in the Canadian Prairies to reduce lodging risk without compromising grain N, but results should be validated in higher precipitation environments and across additional cultivars and growing regions of western Canada.