As a weed, wheat has recently gained greater profile. Determining wheat persistence in cropping systems will facilitate the development of effective volunteer wheat management strategies. In October of 2000, glyphosate-resistant (GR) spring wheat seeds were scattered on plots at eight western Canada sites. From 2001 to 2003, the plots were seeded to a canola–barley–field-pea rotation or a fallow–barley–fallow rotation, with five seeding systems involving seeding dates and soil disturbance levels, and monitored for wheat plant density. Herbicides and tillage (in fallow systems) were used to ensure that no wheat plants produced seed. Seeding systems with greater levels of soil disturbance usually had greater wheat densities. Volunteer wheat densities at 2 (2002) and 3 (2003) yr after seed dispersal were close to zero but still detectable at most locations. At the end of 2003, viable wheat seeds were not detected in the soil seed bank at any location. The majority of wheat seedlings were recruited in the year following seed dispersal (2001) at the in-crop, prespray (PRES) interval. At the PRES interval in 2001, across all locations and treatments, wheat density averaged 2.6 plants m−2. At the preplanting interval (PREP), overall wheat density averaged only 0.2 plants m−2. By restricting density data to include only continuous cropping, low-disturbance direct-seeding (LDS) systems, the latter mean dropped below 0.1 plants m−2. Only at one site were preplanting GR wheat densities sufficient (4.2 plants m−2) to justify a preseeding herbicide treatment in addition to glyphosate in LDS systems. Overall volunteer wheat recruitment at all spring and summer intervals in the continuous cropping rotation in 2001 was 1.7% (3.3 plants m−2). Despite the fact that volunteer wheat has become more common in the central and northern Great Plains, there is little evidence from this study to suggest that its persistence will be a major agronomic problem.

Sulfentrazone is a phenyl triazolinone herbicide used for control of certain broadleaf and grass weed species. Sulfentrazone persists in soil and has residual activity beyond the season of application. A laboratory bioassay was developed for the detection of sulfentrazone in soil using root and shoot response of several crops. Shoot length inhibition of sugar beet was found to be the most sensitive and reproducible parameter for measurement of soil-incorporated sulfentrazone. The sugar beet bioassay was then used to examine the effect of soil properties on sulfentrazone phytotoxicity using 10 different Canadian prairie soils. Concentrations corresponding to 50% inhibition (I50values) were obtained from the dose–response curves constructed for the soils. Sulfentrazone phytotoxicity was strongly correlated to the percentage organic carbon (P = 0.01) and also to percentage clay content (P = 0.05), whereas correlation with soil pH was nonsignificant (P = 0.21). Because sulfentrazone phytotoxicity was found to be soil dependent, the efficacy of sulfentrazone for weed control and sulfentrazone potential carryover injury will vary with soil type in the Canadian prairies.

Canola (Brassica napus L.) is the most important oilseed crop in western Canada. Its prevalence across the Canadian Prairies influences the occurrence and impact of canola volunteers as weeds. Here we determined the persistence of canola seed in cropping systems so effective volunteer management strategies can be developed. In mid‐ to late‐October of 2000, approximately 770 seeds m−2 of glyphosate [N‐(phosphonomethyl)glycine]–resistant (GR) canola were scattered on plot areas at seven western Canadian sites. From 2001 to 2003 the plots were seeded to a wheat (Triticum aestivum L.)–field pea (Pisum sativum L.)–barley (Hordeum vulgare L.) rotation or a fallow–field pea–fallow rotation in five different seeding systems involving seeding dates and soil disturbance levels, and monitored four times each year for canola plant density. Crop seeding date did not consistently influence volunteer canola density. With some exceptions, higher levels of soil disturbance led to higher volunteer canola densities. The vast majority of canola seedlings were recruited in the year following seed dispersal (2001). Across all locations, rotations, and seeding systems, and averaged over preplanting (PREP) and in‐crop prespray (PRES) intervals, canola densities were 6.2, 0.7, and 0.0 plants m−2 in 2001, 2002, and 2003, respectively. Canola volunteers were usually most abundant at PREP and PRES intervals; total recruitment at those intervals averaged across all seeding systems in the continuous cropping rotation was 3% (25 plants m−2). Preventing seed production in new canola volunteers in 2001 reduced canola densities in subsequent years (2002 and 2003) below those required to mitigate weed–crop competition influences in most crops.

. 2006. Agronomic and economic responses to integrated weed management systems and fungicide in a wheat-canola-barley-pea rotation. Can. J. Plant Sci. 86: 1281-1295. Changes in tillage intensity and herbicide use can influence the incidence of weeds, insects and diseases, crop yields and economic returns. We examined the effects of six integrated weed management systems (with varying combinations of tillage methods, seeding rate, seeding date, time when weed control was applied, and annual fungicide applications on pest incidence, grain yield and quality, and economic returns for a spring wheat (Triticum aestivum L.)-canola (Brassica napus L.)-barley (Hordeum vulgare L.)-pea (Pisum sativum L.) rotation in the Dark Brown soils of the Moist Mixed Grassland Ecoregion of Saskatchewan. Herbicide use intensity was reduced without a significant increase in weed biomass in five of the six systems in most crops and years. The complete elimination of herbicides in one system resulted in significant crop yield losses. Certain insects were more prevalent in the cropping systems with early planting dates. Zero tillage systems produced higher yields, and yields generally declined as tillage intensity increased. For all crops, the high herbicide-zero tillage system produced the highest yields, whereas the lowest yields were obtained in the no herbicide-high tillage system. Management method had minimal impact on seed quality. Application of fungicide generally increased yields of barley, wheat and pea, but the increases were not sufficient to recover fungicide cost. High herbicide-zero tillage, medium herbicide-zero tillage, and low herbicide-zero tillage systems produced the highest net return and no herbicide-high tillage system the lowest net return, under all grain price scenarios. En modifiant l'intensité du tallage et l'usage d'herbicides, on peut influer sur l'incidence des mauvaises herbes, des ravageurs et des malades mais aussi sur le rendement de la culture et les recettes. Les auteurs ont examiné les effets de six systèmes de lutte intégrée contre les mauvaises herbes (combinaison variable de méthodes de travail du sol, densité des semis, date d'application de l'herbicide et application annuelle de fongicides) sur l'incidence des ravageurs, le rendement et la qualité du grain, ainsi que les recettes venant d'un assolement blé (Triticum aestivum L.) -canola (Brassica napus L.) -orge (Hordeum vulgare L.) -pois (Pisum sativum L.) cultivé sur les sols brun foncé de l'écozone des prairies mixtes humides de la Saskatchewan. Pour cinq des six systèmes à l'étude, les auteurs ont diminué la quantité d'herbicide employée sans constater de hausse sensible de la biomasse des mauvaises herbes pour la plupart des cultures et la majorité des années. L'élimination complète des herbicides dans un régime a débouché sur une baisse appréciable du rendement des cultures. Certains insectes sont plus pré-valents dans les systèmes agricoles caractérisés par des semis plus précoces. Les systèmes avec non-travail du sol donnent un meilleur ...

Field trials were initiated in fall 2011 to determine the potential of pyroxasulfone to control acetolactate synthase (ALS) inhibitor-resistant weeds in field pea. Pyroxasulfone was applied in split-plot trials at five locations in western Canada using fall and PRE spring applications of 0 to 400 g ai ha−1. Trial locations were chosen with a range of soil organic matter content: 2.9, 4.3, 5.5, 10.5, and 10.6% at Scott, Kernen, Kinsella, Melfort, and Ellerslie, respectively. The herbicide dose required to reduce biomass by 50% (ED50) in false cleavers ranged between 53 and 395 g ha−1at Scott and Ellerslie, respectively. Wild oat ED50s varied between 0.54 g ha−1at Scott in the fall and 410 g ai ha−1in the spring at Melfort. ED50s for wild oat and false cleavers varied by 7.4- and 746-fold, respectively, depending primarily on the organic matter content at the trial location. The effect of application timing was not consistent. Significant yield reductions and pea injury occurred at 150 and 100 g ha−1and higher at Kernen and Scott, respectively. Low organic matter and high precipitation levels at these locations indicates increased herbicide activity under these conditions. Pyroxasulfone may allow control of ALS inhibitor-resistant false cleavers and wild oat; however, locations with high soil organic matter will require higher rates than those with low organic matter for similar control levels.