Weeds represent one of the most important biotic threats to agricultural plant health, and the potential global impact of weeds on crop yields is similar to that of all other pests (animal pests and pathogens) combined. Canola is the most-grown crop in Canada based on seeded area and generates on average Can$29.9 billion in economic activity each year. The objective of this report, sponsored by the Weed Science Society of America Weed Loss Committee, was to provide an updated estimate of potential yield and monetary losses due to weed interference in spring canola grown in Canada and the United States. Quantitative yield data from field experiments were provided by researchers and weed science professionals in the northern Great Plains region; the major canola-producing area of North America. Overall, 89 yield loss estimates were compiled, covering the 18-yr period from 2003 to 2020. Average canola yield losses due to weed interference in Alberta, Saskatchewan, Manitoba, and North Dakota were 35%, 30%, 18%, and 28%, respectively. Potential yield losses weighted by canola harvested area averaged 30%, 28%, and 30% for Canada, the United States, and both countries combined, respectively. Therefore, unfettered weed interference in spring canola represents a potential monetary loss of Can$2.21 billion, $0.16 billion, and $2.37 billion for farmers in Canada, the United States, and both countries combined. The realization of such losses could manifest through continued selection for herbicide-resistant weeds, indicating the critical need for canola farmers to diversify resistance selection pressures by implementing proactive integrated weed management programs.

Limited information exists on the global economic impact of glyphosate-resistant (GR) weeds. The objective of this manuscript was to estimate the potential yield and economic loss from uncontrolled GR weeds in the major field crops grown in Ontario, Canada. The impact of GR weed interference on field crop yield was determined using an extensive database of field trials completed on commercial farms in southwestern Ontario between 2010 and 2021. Crop yield loss was estimated by expert opinion (weed scientists and Ontario government crop specialists) when research data were unavailable. This manuscript assumes that crop producers adjust their weed management programs to control GR weeds, which increases weed management costs but reduces crop yield loss from GR weed interference by 95%. GR volunteer corn, horseweed, waterhemp, giant ragweed, and common ragweed would cause an annual monetary loss of (in millions of Can$) $172, $104, $11, $3, and $0.3, respectively, for a total annual loss of $290 million if Ontario farmers did not adjust their weed management programs to control GR biotypes. The increased herbicide cost to control GR volunteer corn, horseweed, waterhemp, giant ragweed, and common ragweed in the major field crops in Ontario is estimated to be (in millions of Can$) $17, $9, $2, $0.1, and $0.02, respectively, for a total increase in herbicide expenditures of $28 million annually. Reduced GR weed interference with the adjusted weed management programs would reduce farm-gate monetary crop loss by 95% from $290 million to $15 million. This study estimates that GR weeds would reduce the farm-gate value of the major field crops produced in Ontario by Can$290 million annually if Ontario farmers did not adjust their weed management programs, but with increased herbicide costs of Can$28 million and reduced crop yield loss of 95% the actual annual monetary loss in Ontario is estimated to be Can$43 million annually.

Chaff lining and chaff tramlining are harvest weed seed control (HWSC) systems that involve the concentration of chaff material containing weed seed into narrow (20 to 30 cm) rows between or on the harvester wheel tracks during harvest. These lines of chaff are left intact in the fields through subsequent cropping seasons in the assumption that the chaff environment is unfavorable for weed seed survival. The chaff row environment effect on weed seed survival was examined in field studies, and chaff response studies determined the influence of increasing amounts of chaff on weed seedling emergence. The objectives of these studies were to determine the influences of (1) chaff lines on the summer–autumn seed survival of selected weed species and (2) chaff type and amount on rigid ryegrass seedling emergence. There was frequently no difference (P > 0.05) in seed survival of four weed species (rigid ryegrass, wild oat, annual sowthistle, and turnip weed) when seeds were placed beneath or beside chaff lines. In one instance, wild oat seed survival was increased (P < 0.05) when seed were placed beneath compared to beside a chaff line. The pot studies determined that increasing amounts of chaff consistently resulted in decreasing numbers of rigid ryegrass seedlings emerging through chaff material. The suppression of emergence broadly followed a linear relationship in which there was approximately a 2.0% reduction in emergence with every 1,000 kg ha–1 increase in chaff material. This relationship was consistent across wheat, barley, canola, and lupin chaff types, indicating that the physical presence of the chaff was more important than chaff type. These studies suggested that chaff lines may not affect the survival over summer–autumn of the contained weed seeds but that the subsequent emergence of weed seedlings will be restricted by high amounts of chaff (>40,000 kg ha–1).

Oilseed rape seed yield has increased in the last 40 years in most countries, but this yield gain has not been accompanied by greater yield stability. The current study aimed to quantify the genotype by environment (G × E) interaction on oilseed rape yield, identify genotypes with broad adaptability and the main environmental drivers related to seed yield. A weighted two-stage mixed-model analysis was applied to official multi-environment trials of nine spring genotypes (G), in three locations (L) during 6 years (Y) on central and southern Argentine Pampas under rainfed conditions. Best linear unbiased prediction of seed yield ranged from 0.37 to 3.73 kg/ha. Fixed effect L × Y was highly significant and G variability was estimated as 130 kg/ha of standard deviation. Contrasting genotypes were identified by Shukla's stability index and two of those showed the best yield performance in the wettest year. Factor analysis explained 0.75 of total variation and discriminated genotypes with broad and specific adaptability, as well as combined environments according to the similarities in seed yield of the evaluated genotypes. Environmental loadings of Factor 2 were linearly associated with cumulative rainfall in the post-flowering period (up to 230 mm). It is concluded that (i) a significant G × L × Y interaction underlies the high variability of seed yield, (ii) two genotypes (G6 and G7) with high yield stability were identified, and (iii) G × E effects are associated with post-flowering rainfall.

In this study the host plant genotype effect on cabbage aphid, Brevicoryne brassicae (L.)(Hemiptera: Aphididae) preference and performance, the effect of aphid genotype on parasitoids performance, as well as the indirect effects of plant genotypes on aphid parasitoid performance, were tested using different population samples of the aphid and its primary endoparasitoid wasp, Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae). Experiments were run as fully-factorial randomized block design in a greenhouse. Accordingly, host plant cultivar had significant effects on the total number of aphids and aphid-load whilst the fitness of the aphid genotypes were also influenced by plant cultivar. The effect of parasitism on cabbage aphids was significantly different between plant cultivars. Overall, the results revealed that cabbage aphid is under different selective pressures arising from both higher (parasitoid) and lower (host plant cultivar) trophic levels. The host plant cultivar had a significant effect on both aphid fitness and parasitism rate on particular aphid genotypes. This indicates that host-plant-adapted aphid species can create much context-dependency in the nature and strength of ‘fitness benefits parasitism’, which may in turn alter the costs and benefits of host specialization.

Canola (edible rapeseed) crops are often infested by related weed species. This paper addresses effects that seeds from various Brassicaceae weeds may have on canola oil and meal quality. Seeds of common Brassicaceae weeds were collected from canola fields throughout northern Idaho. These were wild mustard, black mustard, birdsrape mustard, shepherd's-purse, flixweed, tumble mustard, and field pennycress. Collected seeds were physically described by weight, size, and shape and were analyzed for oil concentration, fatty acid composition, and glucosinolate concentration. Seed weights ranged from 0.1 to 2 g/1,000 seed. Oil concentration in the weed seeds ranged from 25 to 38%, with erucic acid levels ranging from less than 1 to 47%. Glucosinolate concentration in the mustard weed seeds was over 100 μmol/g oil-free meal, except for shepherd's-purse, which had only 3.4 μmol/g. Using these data, a simple model predicts that both canola oil and seed meal quality can be adversely affected by contamination with weed seeds. Increased erucic acid concentration in modeled admixtures was the most likely oil quality problem associated with weed seed contamination. Glucosinolate concentration in modeled admixtures was higher than acceptable only in those admixtures that also had erucic acid levels that exceeded canola quality standards. Canola-quality oil and seed meal can be maintained with conspicuous weed seed mixtures up to the 2% maximum allowed in U.S. No. 1 canola. However, canola-quality oil and seed meal was not achieved when a 5% weed seed mixture allowed in No. 2 canola was evaluated with the model.

Growth chamber studies were conducted to examine the soil residual properties of DPX-A7881, a new sulfonylurea herbicide. The phytotoxic residue levels in the soil were determined by a lentil radicle bioassay. The duration of activity was prolonged in soil adjusted to pH 7.6 and 8.1 relative to more acidic levels. The rate of breakdown in the soil was enhanced with increased temperature and soil moisture content; a significant temperature by moisture interaction was noted over the duration of the incubation period. The dissipation of DPX-A7881 in soil obeyed first-order kinetics in both studies. An accelerated rate of breakdown in unsterilized versus sterilized soil (pH 7.6) indicated that microbial degradation was an important factor affecting the persistence in alkaline soils. Herbicide residues in the soil caused a reduction in taproot length and number of primary lateral roots of canola seedlings 15 days after planting but there were no other morphological effects observed on the root. The secondary laterals, however, had generally recovered by this time.

Dicamba and 2,4-D, which are used prior to seeding in conservation tillage systems, were applied in late fall and early spring to determine their residual effect on subsequent spring-seeded crops. The herbicides 2,4-D ester and 2,4-D amine with dicamba or glyphosate, applied 0 or 15 d prior to spring seeding, damaged canola, peas, lentils, and alfalfa. The legumes were damaged by spring-applied dicamba. There was also a slight reduction in the total dry matter yield of wheat and barley by 2,4-D applied in spring prior to seeding. All crops tested, except lentils, were tolerant of recommended fall applications of 2,4-D for the control of winter annual flixweed and field pennycress.

In western Canada, seasonal seedling recruitment has been reported in weedy canola populations, and seed persistence has been linked to the secondary seed dormancy potential of a genotype. Temperature influences secondary seed dormancy induction in this species. In these experiments we (1) investigated the influence of temperature and osmotic potential on secondary seed dormancy induction in canola, (2) related these to seedbank dynamics and seedling recruitment of two canola genotypes with different seed dormancy potentials in the field, and (3) investigated the influence of residue, burial depth, and soil type on seedbank dynamics and seedling recruitment in the field. In the laboratory, rates of seed dormancy induction were positively correlated to increasing temperatures and water stress. The role of temperature was approximately threefold more important to seed dormancy development than was osmotic potential within the tested ranges of these variables. In the field, seasonal seedbank dynamics of canola buried at 10 cm were strongly influenced by a genotype's inherent potential for secondary dormancy. An increase in the ungerminable portion of the seedbank was observed in the high-dormancy genotype as soil temperatures increased during spring. This did not occur in the low-dormancy genotype, resulting in sixfold less seed persistence in this genotype by midsummer, by which time, the total remaining seedbank was ungerminable in both genotypes. At the 1-cm burial depth, most of the seedbank was depleted by midsummer of the year after seedbank establishment because of high seedbank mortality in all treatments. Thus, the seasonal recruitment behavior in canola was primarily a function of seed death in the shallow seedbank and a shift to an ungerminable state in the deep seedbank.

Crop rotation has long been considered one of the simplest and most effective tools for managing weeds. In this paper, we demonstrate how crop rotations can be strategically arranged to harness a novel mechanism of weed suppression: weed-weed competition. Specifically, we consider how crop stacking, or increasing the number of consecutive plantings of a single crop within a rotation, can decrease the size of the weed seed bank, by forcing weeds to compete with each other in similar environments for longer periods of time, while still reaping the traditional benefits of crop rotation. Using an annual plant model, we investigate the theoretical effects of stacked crop rotations on weeds that have different life-history strategies and phenology. Our results show that when weeds compete within a season, stacking can reduce the weed seed bank compared to rotations without stacked crops. Although more research is needed to fully understand the effects of crop stacking on other aspects of the system, such as insect pests and diseases, our research suggests that crop stacking has the potential to improve weed suppression without additional inputs, and their associated costs and externalities. More generally, improving management by changing the temporal arrangement of disturbances is a novel, process-based approach that could likely be applied to other weed management practices, such as mowing and herbicide application, and which could involve mechanisms other than weed-weed competition. Leveraging this new application of existing ecological theory to improve weed management strategies holds great promise.

We used laboratory and field feeding trials to investigate adult carabid beetle preferences for three brassicaceous weed species (rapeseed, wild mustard, and field pennycress) that are pests in canola. All carabid species preferred seeds of rapeseed most and those of field pennycress least and showed intermediate preference for wild mustard seeds. Beetles highly preferred imbibed seeds of all three weed species. Activity–density of carabids and mean weed seed removal were highly correlated in field plots of canola, with activity–density accounting for 67% of the observed variation in seed removal. Our study indicates that seed consumption among carabids is influenced by several factors, including weed species, physiological state of seeds, and carabid activity–density. Carabid seed predation is significant in canola agroecosystems; therefore, understanding these influences has implications for ecological weed management.

The presence of volunteer canola is becoming a significant agro-ecological concern, given the large-scale use of herbicide-tolerant varieties in some areas. Our goal was to estimate the frequency and persistence of volunteer canola in Québec cropping systems by surveying fields that included a single canola crop since 1995. A survey was conducted in 131 fields in the main canola-growing areas of Québec: in the Saguenay-Lac Saint-Jean region and the Québec City–La Pocatière area. Volunteer canola plants were counted in 0.25-m2 quadrats every 10 m along a W pattern, and every 15 m along the margins of 88 fields. Volunteer canola plants were found in 90% of the fields surveyed and in a wide range of crops, including cereal, corn, and soybean. Average densities of 4.9 and 3.9 plants/m2 were found 1 yr after canola production in fields and field margins, respectively. Volunteer canola densities decreased significantly over time. However, volunteer plants were still present at low densities 4 and 5 yr after production. Dense stands of volunteer canola were found before postemergence herbicide application in no-till fields (9.8 ± 4.1 plants/m2), suggesting that, contrary to what was suggested in the literature, seeds could become dormant in no-till as well as in tilled systems. A small proportion of the volunteer canola plants observed in no-till fields near Québec City and Ottawa included plants that had overwintered, either originating from fall-germinated seedlings, harvested adult plants that had grown new leaves before the onset of winter, or spring regrowth from the base of unharvested adult plants from experimental plots. The presence and persistence of low densities of volunteer canola may not have been a cause of concern until now. However, producers should be made more aware of the potential short-and long-term problems associated with potential gene flow between different herbicide-tolerant canola (HT canola) varieties and also between HT canola and related weed species.

Previous research has demonstrated that late and sequential applications of glyphosate and glufosinate can have adverse effects on glyphosate- and glufosinate-resistant canola. Similarly, imidazolinone (IMI)-resistant canola may be affected negatively by late applications of imidazolinone herbicides. Field trials were established across the Northern Great Plains region from 2010 to 2012 to examine the response of IMI-resistant canola yield, yield components, and seed quality to late and sequential applications of imazamox. Plots received either a single imazamox application at the two-leaf, six-leaf, bolt, or early bloom stages or sequential applications at the two-leaf followed by six-leaf, two-leaf followed by bolting, and two-leaf followed by early bloom stages; an unsprayed control was included for comparisons. Results indicated that in most site-years there was no effect of imazamox application timing on IMI-resistant canola yield, yield components, or seed quality. These results suggest that late and sequential applications of imazamox to IMI-resistant canola should have little effect on canola production, even if they are made beyond the recommended six-leaf stage. In situations where growers are forced to make late applications (beyond six leaves) to IMI-resistant canola, using solely imazamox appears to minimize adverse effects on seed yield and quality.

Imazamox is an imidazolinone herbicide being developed for weed control in imidazolinone-resistant wheat (IMI-wheat) cultivars and various legume crops. In a series of studies conducted under a range of dryland cropping environments in the Pacific Northwest United States, imazamox applied to IMI-wheat or pea injured barley and canola grown 1 yr after imazamox treatment in low-rainfall, low–soil pH locations of Oregon. Injury was not observed in higher rainfall locations near Pullman, WA. Non–herbicide-resistant wheat planted 1 yr after IMI-wheat treated with imazamox was not injured. Of particular concern for imazamox carryover are low-rainfall areas with low-pH soils. Reduced soil moisture appears to limit imazamox degradation. Imazamox sorption is reduced in low-pH soils, which increases its bioavailability, thereby increasing the potential for injury to rotational crops such as barley, canola, and spring wheat.

Flax is in the process of development as a crop for bio-industrial and nutraceutical products predicated on the use of genetic modification. Before genetically modified (GM) flax is commercially released, effective management practices should be developed to minimize adventitious presence (AP) of GM volunteer flax in subsequent crops. Field research was conducted at four locations during 2007 and 2008 in central Alberta to quantify and mitigate AP of volunteer flax in glufosinate-resistant (GR) and imidazolinone-resistant (IR) canola. A single preplant application of glyphosate at 1,250 g ae ha−1 in GR canola reduced volunteer flax density from 54 to 3 plants m−2 and seed production from 5,963 to 233 seeds m−2. Similarly, the recommended rate of POST glufosinate (600 g ai ha−1) alone effectively controlled volunteer flax and reduced flax seed viability to < 8% and AP to 0.2%. A combination of preplant (glyphosate) and POST (glufosinate) at recommended rates reduced volunteer flax seed production, yield, and AP to near zero in GR canola. Glyphosate applied preplant was equally effective in IR canola, reducing volunteer flax density from 56 to 2 plants m−2, and seed production from 5,571 to 472 seeds m−2. Imazamox + imazethapyr applied POST at all the rates poorly controlled volunteer flax and, even in combination with preplant glyphosate, cannot be recommended for control of flax volunteers in IR canola.

Winter wheat is the predominant crop in Oklahoma, but winter annual grasses are becoming increasingly difficult to control. Summer crop rotations have not been generally adopted; it was decided, therefore, to use winter canola in a crop rotation. However, very little is known about how well herbicides used in canola production will control the winter annual grasses found in Oklahoma wheat fields. Thus, an experiment was conducted at three sites, and repeated the following year, to determine the efficacy of trifluralin, quizalofop, clethodim, and glyphosate in canola production. The weeds evaluated in the experiment were Italian ryegrass, feral cereal rye, and volunteer wheat, along with two varieties of canola: a glyphosate-resistant variety and a conventional variety. All herbicides effectively controlled volunteer wheat. Feral cereal rye and Italian ryegrass varied in response to the herbicide treatments. Trifluralin followed by (fb) quizalofop and glyphosate fb glyphosate were effective on all target species across locations. Effective control of grass weeds was obtained in both conventional and glyphosate-resistant winter canola. Most herbicide treatments improved canola yield over the nontreated check. This experiment demonstrates that Oklahoma wheat producers can effectively rotate to canola to use other herbicides for control of problematic grassy weeds.

A 4-year study was initiated in 1997 to provide canola producers with information on the consequences of various rotational intervals with the use of new disease and herbicide-resistant canola varieties. The study was conducted at three locations in Alberta, Canada (Ellerslie, Strathmore, and Warburg). At each location, four canola rotations were established: continuous canola, and canola seeded in 1 of 2, 3, or 4 years. Canola varieties included the conventional varieties ‘AC Excel’ and ‘Quantum’, the glyphosate-resistant variety ‘Quest’, imidazolinone-resistant ‘45A71’, and a glufosinate-resistant hybrid, ‘Invigor 2153’. In the fourth year of the study, when canola was grown in all treatments, weed densities, weed species diversity, and evenness were determined preseeding and before and after in-crop herbicide application. Canola yield was greatest in the northern ecoregions of the Boreal Transition (Warburg) and Aspen Parkland (Ellerslie), and lowest in the Moist Mixed Grassland ecoregion (Strathmore). Weed populations increased and population diversity decreased and became less even where rotations were less diverse; in continuous canola and in the 1-in-4–year rotation. As expected, weed densities increased in poorly competitive, conventional canola varieties compared to herbicide-resistant varieties sprayed with their broader-spectrum herbicides. Where weed densities were high, variety/herbicide system became a critical factor affecting crop yield. Under these conditions, the herbicide-resistant varieties ‘Quest’ and ‘Invigor 2153’ typically outyielded the conventional varieties of ‘AC Excel’ and ‘Quantum’. Canola yield was highest when grown in a 1-in-3– or a 1-in-4–year rotation, although the 1-in-3–year rotation generally had lower weed densities, and allowed high-value canola to be grown more frequently in rotation.

Seed dormancy is a critical factor in determining seed persistence in the soil and can create oilseed rape (Brassica napus L.) volunteer problems in subsequent years. A 3-year field trial in south-west Germany investigated the effects of seed maturity on primary dormancy and disposition to secondary dormancy of ten oilseed rape varieties (lines) in 2009 and 2010, and of five imidazolinone-tolerant varieties (hybrids) in 2014. Fresh seeds were sampled weekly from about 30 d after flowering (DAF) until full maturity and tested for dormancy on the day of seed collection. Primary dormancy decreased from a high level of 70−99% at 30−40 DAF to 0−15% after 7−14 d, coinciding with embryo growth and depending on variety and year. For some oilseed rape varieties, 30−50% primary dormancy was still present in mature seeds. Depending on variety, disposition to secondary dormancy was nearly zero at the early stage of seed development, increased to its highest level during development, and decreased afterwards. Some varieties maintained a high level of secondary dormancy at maturity or during the entire seed development period. The correlation between primary dormancy and secondary dormancy was significantly positive at early seed development (r = 0.95, 50 DAF), but declined in mature seeds. Environmental conditions during ripening are also expected to affect dormancy dynamics. The deeper insights into dormancy formation of oilseed rape provide the possibility to improve harvest time and harvest method, and to better assess the potential for volunteer oilseed rape in following crops.

The effects of rapeseed and soya bean expeller (SBE) supplementation on digestion and milk production responses in dairy cows were investigated in an incomplete Latin square design using five cows and four 3-week periods. The experimental diets consisted of five concentrate treatments fed at a rate of 9 kg/day: a mixture of barley and oats, which was replaced with rapeseed or SBE at two levels (CP concentration (g/kg dry matter (DM)) of 130 for the control concentrate and 180 and 230 for the two protein supplemented levels). A mixture of grass and red clover silage (1:1) was fed ad libitum and it had a CP concentration of 157 g/kg DM. Supply of nutrients to the lower tract was measured using the omasal canal sampling technique, and total digestion from total faecal collection. Protein supplementation increased omasal canal amino acid (AA) flows and plasma concentrations of AA, and was also reflected as increased milk production. However, N use efficiency (NUE) decreased with increased protein supplementation. Rapeseed expeller (RSE) tended to increase silage DM intake and elicited higher milk production responses compared with SBE and also resulted in a higher NUE. The differences between the protein supplements in nitrogen metabolism were relatively small, for example, there were no differences in the efficiency of microbial protein synthesis or omasal canal flows of nitrogenous components between them, but plasma methionine concentration was lower for soya bean-fed cows at the high CP level in particular. The lower milk protein production responses to SBE than to RSE supplementation were at least partly caused by increased silage DM and by the lower methionine supply, which may further have been amplified by the use of red clover in the basal diet. Although feed intake, diet digestion, AA supply and milk production were all consistently improved by protein supplementation, there was a simultaneous decrease in NUE. In the current study, the milk protein production increased only 9% and energy-corrected milk production by 7% when high level of protein supplementation (on average 2.9 kg DM/day) was compared with the control diet without protein supplementation showing that dairy production could be sustained at a high level even without external protein supplements, at least in the short term. The economic and environmental aspects need to be carefully evaluated when decisions about protein supplementation for dairy cows are taken.

Effects of constant rearing temperature and the plant species fed upon by its hosts were investigated for several developmental parameters of Diadegma semiclausum (Hellén), an important parasitoid of the diamondback moth, Plutella xylostella (L.). Temperature had highly significant effects on all developmental parameters measured, and effects were usually both linear and quadratic with increasing temperature. Host plant species, comprising Brassica napus L., Brassica rapa L. ssp. pekinensis and Brassica oleracea L. var. capitata, also affected development of the parasitoid, and significant interactions were observed between plant species and rearing temperature for all developmental parameters measured. Development of D. semiclausum occurred successfully on all host plant species tested for the temperature range of 10 to 25°C. However, when its P. xylostella hosts consumed leaf tissue of B. napus, no specimens survived to pupate at 30°C, whilst pupation and adult eclosion occurred at 30°C on B. rapa ssp. pekinensis and B. oleracea var. capitata. At high ambient temperatures, such as those characteristic of tropical or subtropical regions (especially at low elevations) or regions that undergo temperature increases due to climate change, P. xylostella is predicted to occur at a higher range of temperatures than its biocontrol agent, D. semiclausum. Effects of high temperatures are expected to be more profound on the parasitoid for some host plants than others, with greater developmental limitations for the parasitoid on B. napus than on B. rapa or B. oleracea.