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Germinated seeds of wild oat populations that were susceptible (S) or resistant (R) to triallate at the recommended soil-applied rate (1.7 kg/ha) were treated with six triallate concentrations on filter paper in petri dishes. Measurement of shoot length 8 d after treatment provided an accurate indication of differences among populations, and was more reliable than determining shoot fresh weight. ED50values (herbicide concentrations that reduced shoot length by 50% relative to untreated controls), derived from nonlinear regression analysis, indicated four and five levels of response to triallate among eight S and seven R populations, respectively. The ED50values varied from 0.11 to 11 ppm a.i. triallate for the most susceptible to the most resistant populations, respectively. Routine testing of wild oat samples suspected of resistance, at triallate concentrations of 0.5 or 1 ppm in the petri dish bioassay, effectively identified populations that had become resistant to the recommended soil-applied rate.

The use of conservation tillage management in fallow cropping systems reduces soil erosion and improves soil quality. The economic benefits of these alternate tillage methods are less certain. This study examined the economic returns from reduced tillage methods on fallow using yield and input data from two experiments at the Agriculture and Agri-Food Canada Research Centre at Lethbridge, Alberta. One experiment was long-term study initiated in 1955 with eight treatments, the second was a 5-yr study with 15 treatments. Results from the 5-yr study indicated no difference in net returns between conventional and reduced tillage fallow systems. In contras, the long-term study net returns were highest for tilled systems and lowest for herbicide-only systems. The long-term study had a build-up of weeds that are difficult to control with herbicides alone. The resulting lower average yield and higher herbicide costs of the herbicide-only treatments in the long-term study accounted for most of the contrasting results between the two experiments. An economic evaluation of tillage practices requires the entire system to be evaluated, not just the tillage component. Key words: Economics, tillage, reduced tillage, conservation practices, weed control

Wild oat populations resistant to triallate have been identified in Alberta. Dose response experiments were conducted in the greenhouse to determine if triallate-resistant wild oat was controlled by other selective wild oat herbicides. Triallate-resistant wild oat populations were effectively controlled by atrazine, ethalfluralin, fenoxaprop-P, flamprop, imazamethabenz, and tralkoxydim. EPTC and cycloate, which are chemically related to triallate, differed in their efficacy on triallate-resistant wild oats. EPTC at the 0.25x field use rate was more efficacious on triallate-resistant than triallate-susceptible wild oat. In contrast, cycloate at the 0.25 to 0.5x field use rate was less efficacious on triallate-resistant than susceptible wild oats. At higher rates, both EPTC and cycloate killed triallate-resistant wild oat populations. Growers have several herbicide choices to selectively control triallate-resistant wild oat in prairie field crops but should plan to rotate herbicides among different chemical families and adopt integrated weed management practices to reduce the risk of these wild oat populations developing resistance to other wild oat herbicides.

Vegetative growth response of round-leaved mallow to various day/night temperature regimes was studied under controlled-environment conditions to predict its potential geographic distribution and to develop an effective control program. Round-leaved mallow dry matter production was greatest with day temperatures of 18 to 26 C. Dry matter accumulation was reduced by a night temperature of 6 C but was minimally affected by night temperatures ranging from 12 to 24 C. Regression analysis predicted minimal vegetative growth at mean daily temperatures below 8 C and above 30 C, with optimum growth at 20 C. Partitioning of round- leaved mallow biomass in leaves, stems, and roots was af- fected by temperature. Maximum leaf weight ratio occurred at low temperatures, 10 C day and 6 C night. Stem weight ratio was greatest at a day temperature of 26 C, with night temperature having little effect. Maximum root biomass oc- curred with a day temperature of 18 C. Results are discussed in terms of environmental conditions that allow round- leaved mallow to be an effective competitor with crops and potential approaches for its control. Nomenclature: Round- leaved mallow, Malva pusilla Sm. #3 MALPU.

Summary The vegetative growth response of Erodium cicutarium (L.) ĽHer. ex Ait. to various day:night temperature regimes was studied under controlled environment conditions. Dry matter production was greatest with day temperatures of 18 to 34^C combined with night temperatures of 12 to 18^C. A high night temperature of 24^C was very detrimental, reducing dry matter production to 15 to 25% of that attained at 12^C. The optimum mean daily temperature for growth of E. cicutarium is predicted to be in the range 17 to 20^C. Little growth is predicted at mean daily temperatures below 5^C and above 30^C. Partitioning of biomass in leaves, stems and roots was markedly affected by day and night temperatures. Stem weight ratio was greatest at day temperatures of 18 to 34^C and night temperatures of 18 to 24^C. Maximum leaf weight ratio occurred at day and night temperatures of 10 to 18^C. Root biomass was little affected by day temperatures, but was greatest at a night temperature of 12^C, declining substantially as night temperature increased from 12 to 24^C. Results are discussed in terms of the potential for E. cicutarium to become an increasingly troublesome weed in crops of the Canadian prairies and in terms of possible management strategies for its control.

Few postemergence (POST) herbicides provide adequate control of broadleaf weeds in potato. Field experiments were conducted at Lethbridge and Vauxhall, Alberta in 1991 and 1992 to determine the suitability of rimsulfuron and HOE-075032 for selective POST control of weeds in potato. Rimsulfuron applied at 15 to 30 g ai/ha controlled flixweed, kochia, and redroot pigweed and suppressed the growth of redstem filaree. HOE-075032 at 50 to 60 g ai/ha provided comparable control. The potato cultivars, 'Shepody,' 'Norchip,' 'Russet Burbank,' 'Niska,' and 'Ranger Russet,' tolerated up to 80 g/ha rimsulfuron, but rimsulfuron at 120 g/ha caused fissures in some tubers and reduced marketable and total tuber yields. Tuber quality factors such as specific gravity and chipping ability were not affected by rimsulfuron. HOE-075032 at 15 to 30 g/ha caused fissures in tubers and reduced marketable and total tuber yield of all potato cultivars. Rimsulfuron, but not HOE-075032, provided excellent selective POST broadleaf weed control in potato. Nomenclature: HOE-075032, 3-(4,6-dimethoxypyrimidin-2-yl)-1-(N-methyl-N-methylsulfonyl-aminosulfonyl)-urea; rimsulfuron, N-[[(4,6-dimethoxy-2-pyrimidinyl)-amino]carbonyl]-3-(ethylsulfonyl)-2-pyridinesulfonamide; flixweed, Descurainia sophia L. Webb ex Prantl # 3 DESSO; kochia, Kochia scoparia (L.) Schrad. # KCHSC; redroot pigweed, Amaranthus retroflexus L. # AMARE; redstem filaree, Erodium cicutarium (L.) L'Her. ex Ait. # EROCI; potato, Solanum tuberosum L. 'Russet Burbank.'

Downy brome control in winter wheat is often inadequate. The effects of three crop rotations and two tillage intensities on downy brome populations and associated crop yields were determined in an experiment at Lethbridge, Alberta from 1987 to 1993. Downy brome densities in continuous winter wheat increased from 24 to 970 plants/m2between 1988 and 1993; and were often higher with zero tillage. Inclusion of fallow or spring canola in rotation with winter wheat suppressed downy brome densities to less than 55 and 100 plants/m2, respectively, over the six years. In continuous winter wheat, yields decreased as downy brome densities increased progressively over years, indicating that monoculture winter wheat production will not be viable in regions where downy brome is prevalent unless effective herbicides are developed. In the more arid areas of the Canadian prairies, a winter wheat-fallow rotation may be most suitable but in higher precipitation areas, a winter wheat-canola rotation is a viable alternative. Crop rotation is a key component of an improved management system for control of downy brome.

Downy brome (Bromus tectorum L.) causes large yield reductions in winter wheat (Triticum aestivum L.) in the western USA and Canada. Current control practices using fallow and preseeding tillage often are ineffective. A study was conducted over 3 yr at Lethbridge, AB, to determine if winter wheat cultivars varying in height and growth habit differ in their competitive ability with downy brome. A factorial set of treatments included downy brome at 0, 10, 50, and 200 plants m −2 grown with winter wheat cultivars Norstar, Redwin, Archer, and Norwin. Downy brome reduced the biomass and seed yield of all cultivars in all years, but the magnitude of the yield reductions differed among cultivars. Downy brome caused 14 to 30% greater yield reductions in the semidwarf cultivars, Archer and Norwin, than in the tall cultivars, Norstar and Redwin [...]

In response to farmer complaints of poor triallate performance, wild oat seed was collected from 34 fields in Alberta in the fall of 1990. Screening trials in the greenhouse indicated that 15 of the populations were highly resistant to triallate applied at the equivalent of the recommended field rate (1.7 kg ha-1), whereas the other 19 populations were adequately controlled. All triallate-resistant populations were also highly resistant to difenzoquat applied at 1.7 kg ha-1(equivalent to twice the recommended field rate). The effect of increasing rates of both herbicides on dry weight of five of the resistant and two of the susceptible populations was determined in greenhouse experiments. Triallate applied up to 3.4 kg ha-1had little or no effect on the resistant populations, whereas the susceptible populations were controlled at 1.7 kg ha-1. At rates of 6.8 kg ha-1or higher, there were differences among the resistant populations and among individuals within the populations in the response to triallate. Response of the resistant populations to increasing difenzoquat rates was variable between experiments, but in all cases the effect of difenzoquat on wild oat dry weight was considerably less in triallate-resistant than triallate-susceptible populations. Effects of increasing rates of triallate and difenzoquat on resistant and susceptible wild oat populations growing with barley in field experiments were generally similar to the responses in the greenhouse.

Soil erosion by wind or water is a serious problem in North and South America. When no-till or reduced tillage is used to control erosion, the density of certain annual and perennial weeds can increase and new weed control techniques are usually required. The effects of conservation tillage on annual and perennial weeds, weeds that are spread by wind, plants from rangelands and pasture as weeds and volunteer plants as weeds are reviewed. Current weed control methods with minimum tillage, herbicides, cover crops and other cultural practices in conservation tillage systems in North and South America are described. Some producers are successfully controlling weeds in continuous summer cropping systems in North America and in double cropping systems that include wheat in the winter and soybean or corn in the summer in Brazil, Argentina and southeastern United States. Successful conservation tillage systems usually involve cropping sequences of three or more crop types and several herbicides. In these cropping sequences, the ground is covered with a crop during most of the period in which the climate is favourable for weed growth. Perennial weeds are a problem in all tillage systems and there is a general dependence on glyphosate for perennial weed control. In successful conservation tillage systems, the amount and cost of herbicides used is similar to that for herbicides used in conventional tillage systems.

Experiments were conducted for 4 yr at Lethbridge and Brooks, Alberta, and at Morden, Manitoba, to determine the effect of seeding date, cultivar (Saffire, S-208 and Cargill-3) and location on safflower (Carthamus tinctorius L.) yield, oil content, test weight and maturity; and the effect of accumulated degree–days (DD) on yield, oil content and test weight. The early-maturing cultivar, Saffire, produced the least variable yields across seeding dates. For locations and years where fall frosts did not occur before maturity, Cargill-3 produced good yields, even with late seeding; S-208 yielded less in similar situations; however, S-208 generally outyielded Saffire. Highest yields were obtained at Brooks by seeding in late April, at Lethbridge, by seeding in late April or early May. However, at both Alberta locations, Saffire could usually be seeded to mid-May without major yield reduction. At Morden, seeding during the third week of May provided optimum yields. Seeding date had little influence on oil content. Later seeding dates tended to reduce days to maturity and test weight. Safflower matured 3 wk earlier at Morden (earliest site) than at Lethbridge (latest site), with maturity at Brooks averaging 4–8 days earlier than at Lethbridge. Plants required more DD to reach maturity at Morden than at either Alberta location. DD was positively associated with yield of S-208 at both Lethbridge and Morden; for Saffire, only at Lethbridge; and for Cargill-3, only at Morden. DD generally did not significantly affect oil or test weight. Key words: Safflower, Carthamus, agronomy, seeding dates, yield, oil, test weight, maturity, degree–days

Knowledge about the prevalence and diversity of antibiotic resistance genes in soil bacteria communities is required to evaluate the possibility and ecological consequences of the transfer of these genes carried by genetically modified (GM) plants to soil bacteria. The neomycin phosphotransferase gene (nptII) conferring resistance to kanamycin and neomycin is one of the antibiotic resistance genes commonly present in GM plants. In this study, we investigated kanamycin-resistant (Km(R)) and neomycin-resistant (Nm(R)) soil bacterial populations in a 3-year field trial using a commercial GM corn (Zea mays L.) carrying the nptII gene and its near isogenic line. The results showed that a portion (2.3 - 15.6 %) of cultivable soil bacteria was naturally resistant to kanamycin or neomycin. However, no significant difference in the population level of Km(R) or Nm(R) soil bacteria was observed between the GM and non-GM corn fields. The nptII gene was not detected in any of the total 3000 Km(R) or Nm(R) isolates screened by PCR. Further, total soil bacterial cells were collected through Nycodenz gradient centrifugation and bacterial community DNA was subjected to PCR. Detection limit was about 500 cells per gram of fresh soil. Our study suggests that the nptII gene was relatively rare in the soil bacterial populations and there was no evidence of gene transfer from a GM corn plant to soil bacteria based on the data from total soil bacterial communities.

Field experiments over 3 yr at Lethbridge, Alberta, determined the effect of various downy brome densities and times of its emergence on winter wheat biomass and seed yield. Downy brome reduced wheat biomass up to 59% and seed yield up to 68%. Time of downy brome emergence relative to wheat affected the magnitude of these yield reductions more than the density of downy brome. At comparable densities, downy brome caused 2- to 5-fold greater reductions in yield when it emerged within 3 wk after winter wheat than when it emerged 6 wk after wheat or in early spring. Late-emerging downy brome caused significant wheat yield or biomass losses only at densities of 200 to 400 plants m-2. Late-emerging downy brome plants were strongly shaded (70 to 90%) by winter wheat throughout much of the growing season.

One year after application under irrigated conditions, atrazine at 1.2 kg/ha injured oat but there was no effect after two years. On dryland, wheat and barley were injured for up to two years after atrazine was applied at 1.5 kg/ha. Atrazine concentrations in the soil were related to accumulated rainfall in an exponential equation. The equation predicted that, under the most severe drought conditions ever recorded for southern Alberta, injury to cereal crops could occur for at least three years after atrazine application at 1.2 to 1.5 kg/ha. Cyanazine did not injure subsequent crops under either irrigated or dryland conditions.

Field experiments over 3 yr at Lethbridge, Alberta, determined the effect of various downy brome densities and times of its emergence on winter rye biomass and seed yield. Downy brome reduced yields most when it emerged within 3 wk of rye, but densities of more than 100 downy brome m-2were required to reduce yields by 20 to 30%. The greatest reductions in rye biomass (28%) and seed (33%) yields over the 3 yr occurred when 400 downy brome m-2emerged with the crop. Downy brome, at densities up to 400 plants m-2, emerging 6 wk after rye or in early spring, reduced rye biomass and seed yield less than 10% in all years. Winter rye effectively shaded downy brome (40 to 90%) for much of the growing season.

Field experiments were conducted in 1990 and 1991 at Lethbridge, Alberta, to determine if narrower row spacings and increased plant densities than commonly practiced would improve safflower's competitive ability with weeds. A factorial set of treatments of safflower at two row spacings of 11 and 22 cm and six densities ranging from 10 to 192 plants m−2grown weed free or infested with green foxtail (Setaria viridis(L.) Beauv.). Decreasing safflower row spacing from 22 to 11 cm slightly improved competition with green foxtail, but increasing safflower density had a much greater effect. Weed-free safflower biomass and seed yield plateaued at 70 and 84 plants m−2in 1990 and 1991, respectively. However, safflower infested with 500 plants m−2of green foxtail increased in biomass and seed production up to 100 plants m−2in 1990 and 156 plants m−2in 1991. At these high densities, weedy safflower yielded less than weed-free safflower but three to four times more than achieved at lower stand densities. Concurrently, high safflower density reduced green foxtail biomass up to 72% and seed yield up to 85%. Dense safflower stands developed a closed canopy early in the season and shaded green foxtail more than thin stands.

Field studies were conducted to study the interaction of sethoxydim or fluazifop-P with clopyralid and/or ethametsulfuron applied as tank mixtures to canola. Control of the indicator species barley, broadbean, and wild mustard with the tank mixtures was comparable to, or sometimes better than, that attained with each herbicide alone. Canola tolerated all herbicides applied individually and all tank mixtures of these herbicides except fluazifop-P and ethametsulfuron. Tank mixtures of fluazifop-P and ethametsulfuron, with or without clopyralid included in the mixture, suppressed early growth of canola in two of four tests and reduced seed yield in one. Sethoxydim, clopyralid, and ethametsulfuron combined in tank mixtures provide an effective POST alternative for selective control of grass and broadleaf weeds in canola.

A study was conducted under controlled environmental conditions to determine the effect of soil temperature, soil moisture, and depth of seed burial on the emergence of redstem filaree. Emergence occurred from 5 to 30 C but was optimal at 5 to 15 C. Redstem filaree emergence was optimal in moist soil with water contents of −0.03 to −0.28 MPa. Emergence progressively decreased as soil moisture was lowered below these levels, with less than 25% emergence attained at −1.53 MPa regardless of soil temperature. Almost no germination was observed in warm (30 C), dry (-1.03 to −1.53 MPa) soils. Rate of emergence was affected more by soil temperature than by moisture. A decrease in temperature from 20 to 5 C increased the time to reach 50% emergence by 6 to 8 d but a decrease in soil moisture from −0.03 to −1.53 MPa increased the time to reach 50% emergence by only 1 to 2 d. Emergence was greatest at soil depths of 1 cm or less. No emergence occurred at depths of 8 cm or below.

Field studies were conducted to determine suitability of flurtamone alone and in tank mixture with ethalfluralin for selective control of weeds in safflower. Flurtamone at 0.6 to 0.9 kg ha71 controlled field pennycress, kochia, and Russian thistle. Flurtamone and ethalfluralin were compatible in tank mixture and provided comparable or superior control of wild oat, kochia, and field pennycress than either herbicide alone. Plant height, date of flowering, seed yield, and quality data indicated that safflower tolerated flurtamone alone up to 1.6 kg ha-l and flurtamone tank mixed with ethalfluralin at rates as high as 1.1 plus 1.1 kg ha-1, respectively. Safflower yield response to these herbicides was positive and reflected level of weed control attained with various treatments. Nomenclature: Ethalfluralin, N- ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(tri- fluoromethyl)benzenamine; flurtamone, 5-(methylamino)- 2-phenyl-4-(3-(trifluoromethyl)phenyl)-3(2H)-furanone; field pennycress, Thlaspi arvense L. #3 THLAR; kochia, Kochia scoparia (L.) Schrad. # KCHSC; Russian thistle, Salsola iberica Sennen & Pau # SASKR; wild oat, Avena fatua L. # AVEFA; safflower, Carthamus tinctorius L.

The aim of integrated weed management (IWM) is to use of a combination of different practices to maintain weed densities at manageable levels. A field experiment was conducted at Agricultural College, Tehran of University, in Karaj city 2005-2006 by planting wheat, to investigate the response of planting methods and tank mixed herbicides. The experiment was laid out using a split plot arrangement, in randomized complete block design with three replications. Methods of planting were assigned to the main plots; while tank mixed herbicdes were kept in the sub-plots. The subplot size measured 4.5 × 4.5 m2. Row to row distance was kept at 30 cm. Data were recorded on weed density m-2, plant height (cm), spike length (cm), Number of spikes m-2, Number of grains spike-1, 1000 grain weight (g), biological yield (kg ha-1), and grain yield (kg ha-1). The data for individual traits were subjected to the ANOVA technique and significant means were separated by the LSD test. The analysis of the data showed that methods of sowing were statistically significant for plant height, No. of grains spike-1, 1000-grain weight and biological yield. The herbicides were statistically significant for all the parameters investigated except No. of grains spike-1, while the interaction of methods of planting with herbicides could not reach the level of significance in any of the traits examined. Among the methods of planting, line sowing was the best followed by line + broadcast sowing. The herbicide mixtures controlled mixed stands of broadleaf and grassy weeds to the tune of 65 to 74% with a consequent increase in grain yield from 58- 107%. Buctril-M + Topik 15 WP, 2,4-D + Puma Super 75 EW and Topik 15 WP were segregated as the top scoring applications by increasing yield to the extent of 107, 104 and 101 %, respectively over the weedy check.

Experiments were conducted at the Lacombe and Lethbridge Research Stations to determine tralkoxy- dim activity at two leaf stages of green foxtail and wild oat and to determine tralkoxydim activity in tank mixtures with bromoxynil and thifensulfuron. Green foxtail and wild oat control was usually better when tralkoxydim was applied at the 2- to 3-leaf stage. However, tralkoxydim applied at the 4- to 5-leaf stage of the weeds often led to less weed topgrowth at harvest because later flushes of green foxtail and wild oat often occurred after the early applications. Nevertheless, wheat and barley yields usually indicated the importance of early weed removal. In greenhouse and field tank mixture studies, thifensulfuron antagonized tralkoxydim activity on green foxtail more than wild oat. Bromoxynil was less antagonistic than thifensulfuron, but significant reduc- tions in green foxtail and wild oat control were detected in tralkoxydim tank mixtures with bromoxynil. In field studies, control of false cleavers with thifensulfuron or bromoxynil was not reduced in tank mixtures with tralkoxydim. Nomenclature: bromoxynil, 3,5-dibromo- 4-hydroxybenzonitrile; thifensulfuron, 3-(((((4-methoxy

(.)Eight years of research on dryland corn in southern Alberta focused on hybrid evaluation, irrigated and dryland comparisons, genotypic responses to drought and density stress, optimum plant density, paired row studies, weed control trials, and a 3-yr farm-scale study of three corn-based rotations. Grain yields of 35 bu/acre on summerfallow were obtained with currently available hybrids for the 2840 growing-degree-day area around Medicine Hat in southern Alberta (.)

Field studies were conducted to identify herbicides suitable for improved control of hairy nightshade, redroot pigweed, and common lambsquarters in pinto beans. Fomesafen at 0.25 kg ai ha-1did not adequately control these weeds. Clomazone at 0.5 kg ai ha-1controlled common lambsquarters but only suppressed the growth of redroot pigweed and hairy nightshade. Ethalfluralin at 0.84 to 1.1 kg ai ha-1gave excellent initial control of these weeds but did not control later flushes of hairy nightshade. Imazethapyr applied PPI or POST at 50 to 75 g ai ha-1controlled hairy nightshade, redroot pigweed, and common lambsquarters throughout the growing season. Imazethapyr combined with ethalfluralin gave superior weed control and resulted in greater yields than the most commonly used herbicides in pinto beans in western Canada.

Field studies were conducted to determine the most effective rate of several herbicides applied at various growth stages to control downy brome in conservation fallow programs. Downy brome growth stage affected the efficacy of all herbicides. All herbicides were less effective when application was delayed until the boot stage of downy brome. Fluazifop-P and sethoxydim must be applied prior to tillering to effectively control downy brome. Glyphosate, the commercial mixture of glyphosate plus 2,4-D, paraquat, and HOE-39866 consistently controlled downy brome up to the 3- to 5-tiller stage. Glyphosate at 180 to 200 g ha-1, paraquat at 250 to 300 g ha-1, and the commercial mixture of glyphosate plus 2,4-D at 600 to 660 g ha-1controlled downy brome 80 to 90%. The effective rates were lower than rates currently registered for downy brome control in western Canada, and thus there is potential for making conservation fallow programs more economical when downy brome is the predominant weed.

Downy brome (Bromus tectorum L.) causes serious yield reductions in winter cereals in the western USA and Canada. Current control practices often are ineffective. A study was conducted under controlled-environment and field conditions to determine the effect of soil temperature (5-30 o C) and moisture (-0.30 to -1.53 MPa) on the rate and total emergence of downy brome relative to that of winter cultivars of canola (Brassica napus L.), wheat (Triticum aestivum L.), and rye (Secale cereale L.) with the aim of developing improved cultural control measures

Field studies were conducted to determine the effect of varying densities of hairy nightshade and varying durations of interference on the biomass and seed yield of dry beans. As few as two hairy nightshade plants per meter of row reduced bean seed yield by an average of 13% over the 2 yr of the study. Increasing the density of hairy nightshade to 100 plants per meter resulted in bean yield losses of 77%. Hairy nightshade interference during the first 3 weeks after crop emergence was sufficient to reduce bean yields. Up to 9 weeks of hairy nightshade-free maintenance after crop emergence was required to prevent bean yield losses. Hairy nightshade was a prolific seed producer. At low infestation densities, over 45 000 seeds per plant were produced. Hairy nightshade seed production peaked at over 300 000 seeds m–1at about 30 plants per m of row. Depending on the length of the growing season, 6 to 9 weeks of weed-free conditions after crop emergence were required to prevent hairy nightshade from producing viable seeds before the first killing frost in the fall. Results are discussed in terms of timing and longevity of control required to reduce hairy nightshade interference in dry beans.

Studies were conducted to determine the effect of ensiling and/or rumen digestion by cattle on the germination and viability of several common weed species. Seed survival of grass species subjected to ensiling and/or rumen digestion tended to be less than that of broadleaf species. Downy brome, foxtail barley, and barnyardgrass were nonviable after either ensiling for 8 weeks or rumen digestion for 24 h. Some green foxtail (17%) and wild oats (0 to 88%) seeds survived digestion in the rumen but were killed by the ensiling process. Varying percentages of seeds of kochia, redroot pigweed, common lambsquarters, wild buckwheat, round-leaved mallow, and field pennycress remained viable after ensiling (3 to 30%), rumen digestion (15 to 98%), and ensiling plus rumen digestion (2 to 19%). A time course study of rumen digestion indicated that loss of seed viability often was not a gradual process. With some species, there was an initial lag phase while degradation of the protective seed coat likely occurred, followed by a rapid decline in embryo viability. The diet fed to livestock appeared to affect viability losses caused by rumen digestion. Estimates of seed survival with varying rates of passage through the rumen due to differing ratios of grain to forage in the diet are presented. Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; common lambsquarters, Chenopodium album L. # CHEAL; downy brome, Bromus tectorum L. # BROTE; field pennycress, Thlaspi arvense L. # THLAR; flixweed, Descurainia sophia (L.) Webb. ex Prantl. # DESSO; foxtail barley, Hordeum jubatum L. # HORJU; green foxtail, Setaria viridis (L.) Beauv. # SETVI; kochia, Kochia scoparia (L.) Schrad. # KCHSC; redroot pigweed

Agricultural ecosystem weeds can be invasive species. On the Canadian Prairies, the vast majority of weeds that annually invade crops and interfere with crop production are self-sustaining, non-native species that have spread over large areas. Weeds have vulnerabilities that can be exploited by combining optimal agronomic practices in addition to herbicide application. Some of these practices include competitive cultivars, relatively high crop seed rates, and strategic fertilizer placement. Prairie weeds have been reduced in numbers by the consistent use of herbicides, but herbicide resistance is now a major challenge. Weed resistance and other shifting crop production or environmental factors may significantly alter invasive weed dynamics and crop-weed interactions, and will undoubtedly pose future challenges to crop producers. These and other challenges can be countered by reducing soil disturbance and diversifying cropping systems that combine several synergistic components. There is a need for the implementation of true integrated crop, weed, and pest management systems that are multi-disciplinary. The common alien weed species that persistently invade Prairie cropland each year will not be subdued over the long term in the absence of such systems.

During the period from 2000 to 2013, average canola yields from Canadian farms increased from 1330 to 2025 kg ha–1, or 54 kg ha–1 year–1. The objective of this review was to propose likely reasons behind this increase by examining genotypic, environmental and agronomic factors. During this period, hybrid canola cultivars with herbicide tolerance (HY-HT) expanded from 80% to >95% of the area sown to canola. Genetic gain from switching from open-pollinated cultivars to HY-HT cultivars was estimated to account for 32 kg ha–1 year–1. When some key environmental factors were examined, there were no significant linear changes in growing season temperature, although the linear increase in April and May precipitation was significant and likely responsible for an increase of 12 kg ha–1 year–1. When coupled with the yield increase from changes in atmospheric CO2 (3 kg ha–1 year–1), the environment was estimated to account for ~15 kg ha–1 year–1. Ignoring all main-factor interactions, changes due to management accounted for the remainder, or 7 kg ha–1 year–1. The expanded use of HY-HT varieties has resulted in better weed control, and an increase in the use of minimum tillage, leading to greater water-use efficiency and higher yield. It is likely that many of the effects of changes in management were hidden in the interaction with genotype and environment main effects. It is difficult to estimate these interactions without designing experiments to do so. The design and implementation of experiments to understand the interaction among main factors should be a priority. Future yield targets of 25 Mt canola by 2025 will require an increase in yield per ha beyond the current rate, or an increase in the land seeded to canola, or a combination of the two factors. Continued progress with canola yield depends on active plant-breeding programs, agronomic research using new varieties, favourable environmental conditions, and high world commodity prices.

A study was conducted under controlled envir- onmental conditions to determine the effect of soil temperature, soil moisture, and depth of seed burial on the emergence of round-leaved mallow. Emergence oc- curred from 5 to 30 C but was optimal at 15 to 20 C. Soil moisture had a greater effect than soil temperature on percentage emergence. Emergence progressively declined below a soil water content of -0.28 MPa, with less than 20% emergence attained at -1.03 to -1.53 MPa. In contrast, rate of emergence of round-leaved mallow was affected more by soil temperature than by moisture. A decrease in temperature from 30 to 5 C increased the time to reach 50% emergence by 10 to 12 days over the moisture regime of this study. Emergence was greatest at depths of 0.5 to 2 cm. No emergence occurred at 8 cm or below. The potential of using the findings of this study to develop cultural control strategies for round-leaved mallow is discussed. Nomenclature: Round-leaved mal- low, Malva pusilla Sm. Additional index words. Weed biology, germination, plant- ing depth.

Greenhouse and field studies were conducted to examine the interaction of sethoxydim or fluazifop-P tank mixed with chlorsulfuron or thiameturon for selective weed control in safflower. Under greenhouse conditions, the addition of chlorsulfuron to sethoxydim or fluazifop-P slightly improved the control of green foxtail above that achieved with either herbicide alone. Control of wild oat and wild mustard was similar with the tank mixes and each herbicide alone. In the field, control of wild oat with sethoxydim or fluazifop-P was not altered by adding chlorsulfuron or thiameturon in tank mixes. Similarly, control of common lambsquarters and wild mustard with chlorsulfuron or thiameturon was not affected by adding either sethoxydim or fluazifop-P in tank mixes. Plant height, date of flowering, seed yield, and quality data indicated that safflower tolerated these herbicides applied alone or in combination. Sethoxydim or fluazifop-P tank mixed with chlorsulfuron or thiameturon provide a postemergent alternative for selective control of grass and broadleaf weeds in safflower.

Field studies were conducted in 1986, 1987 and 1988 at Lethbridge, Alberta and in 1987 and 1988 at Indian Head, Saskatchewan to determine herbicides suitable for selective control of weeds in safflower (Carthamus tinctorius L.). Safflower exhibited acceptable tolerance to trifluralin, ethalfluralin, sethoxydim, fluazifop-p-butyl, clethodim, diclofop methyl, difenzoquat, imazamethabenz, chlorsulfuron, thiameturon, metsulfuron and DPX-A7881 over all years and locations. These herbicides offer the grower the option of preplant incorporated or postemergent herbicide application or a combination of the two. A mixture of thiameturon plus DPX-L5300 caused severe injury to safflower, reducing yield, oil content, and seed weight. Desmedipham, phenmedipham, and mixtures of these herbicides injured safflower at Lethbridge but not at Indian Head. Weeds reduced safflower yield by 39–73% over the 3 yr of the study. Control of weeds in safflower is essential to obtain optimum yields.Key words: Crop tolerance, seed yield, oil content, seed weight, weed competition

P. minor is an alien weed with serious environmental and economic consequences. Although there is appreciable progress in the area of P. minor management through herbicides, its ecology still needs to be explored. Vila et al. [57] suggested that there is a need to assess and quantify the impact of alien species at several levels of ecological complexity in order to gain influence in their management and control. Several herbicides are available for P. minor control (Tab. 2); however, the joint action of herbicides with different molecular targets to P. minor management has not been well investigated.

Nine experiments were conducted in Alberta and Manitoba between 1988 and 1991 to determine the effect of row spacing and seeding rates on safflower (Carthamus tinctorius L.) yield, oil content, test weight and maturity. Row spacings of 15 and 30 cm at Morden had little effect on yield, while in southern Alberta there was a tendency toward increased yields with narrow rows (23 cm) compared with wide rows (46 cm). Seeding rates of 32–40 kg ha−1 were required to obtain maximum seed yields. Oil content, test weight, and days to maturity were not consistently affected by row spacing or seeding rate. Key words:Carthamus, row spacings, seeding rates, yield, oil, test weight, maturity

The interaction of DPX-A7881 and clopyralid applied as tank mixtures was studied under controlled environment and field conditions on several commonly occurring weeds in canola. Control of wild mustard and wild buckwheat was not affected by mixing these herbicides. DPX-A7881 controlled wild mustard, and clopyralid controlled wild buckwheat independently of the other herbicide. However, redroot pigweed and common lambsquarters were controlled better with DPX-A7881 plus clopyralid than with either herbicide alone. The herbicides interacted in an additive to synergistic manner on redroot pigweed depending on the rate of each herbicide. DPX-A7881 and clopyralid interacted synergistically at all rates on common lambsquarters. Plant height, date of flowering, seed yield, and quality data all indicated that canola completely tolerated DPX-A7881 and clopyralid applied alone or in combination.