Weed removal experiments in dry edible beans were conducted during 1992 and 1993 at Crookston and Staples, MN. Ten manual weed removal treatments were studied to determine when a natural infestation of weeds first reduced dry bean yield, and when weed removal could be discontinued without further loss of seed yield. Major weeds in order of average biomass production on weedy check plots at dry bean harvest over locations and years were wild mustard, foxtail spp., redroot pigweed, common ragweed, wild buckwheat, hairy nightshade, and common lambsquarters. Hairy nightshade also emerged late in the growing season and could negatively affect harvest efficiency and stain navy beans. Weed removal treatments had little effect on dry bean stands or 100-seed weights of harvested dry bean seed. The critical period for weed control in dry beans was 3 to 5 or 6 weeks after planting (WAP). Thus, weed control practices should begin no later than 3 WAP and continue until at least 5 or 6 WAP for maximum dry bean yields.

The efficacy of sulfonylurea herbicides impregnated on granular fertilizers applied PPI or POST was compared to broadcast spray applications for annual broadleaf weed control in winter wheat. Henbit and bushy wallflower were controlled by chlorsulfuron or triasulfuron impregnated onto diammonium phosphate granular fertilizer applied PPI. Efficacy of these herbicides for annual broadleaf weed control was reduced by applying them POST with granular urea fertilizer carrier instead of with water carrier.

The ability of Medicago sativa to suppress weed growth may provide a viable alternative to chemical weed control and allow crop producers to reduce herbicide inputs. Quantitative information regarding the suppressive effect of M. sativa on weed populations in current cropping systems is lacking. A survey was conducted in Manitoba, Canada, in 1993 and 1994 to investigate weed populations in commercial cereal fields that had been preceded by either M. sativa hay or cereal grain crops. A total of 117 fields were surveyed; approximately half from each field type. Principle component analysis indicated that the inclusion of M. sativa in crop rotations resulted in weed communities different from those of continuous cereal fields. Naturally occurring populations of Avena fatua, Cirsium arvense, Brassica kaber, and Galium aparine were lower in cereal fields that had previously contained M. sativa than in cereal fields that had been preceded by a cereal crop. Lower field uniformity values for C. arvense and Avena fatua indicated that these weeds were also more patchy in the M. sativa rotations. Population differences between field types were nonsignificant for Amaranthus retroflexus, Chenopodium album, and Polygonum convolvulus, and although populations of Taraxacum officinale and Thlaspi arvense were greater in M. sativa/cereal fields than in continuous cereal crops. No consistent effect of field type on Setaria viridis populations was observed. These results show that M. sativa effectively suppressed some, but not all, of the weeds found in the study area. Including M. sativa hay crops in crop rotations can be part of an integrated weed management strategy for weeds such as A. fatua, B. kaber, and C. arvense.

Field studies were conducted in 1996 and 1997 at three locations throughout southern Ontario with the objective of developing dose-response curves of RPA 201772 for weed control and crop tolerance in corn. The biologically effective doses required to control redroot pigweed, velvetleaf, and wild mustard were 100, 90, and 80 g/ha, respectively. Yellow foxtail was controlled with 100 to 120 g/ha, while rates for common lambsquarters varied from 60 to 130 g/ha, depending on the year and location. Wild buckwheat control was poor (> 30%) at all of the doses tested. RPA 201772 did not reduce corn grain yield; however, temporary crop injury was evident on coarse sandy soils.

Barnyardgrass and many broadleaf weeds were severely stunted by POST applications of isoxaben. Most grasses were only moderately affected by isoxaben at rates up to 1 kg/ha. POST activity was enhanced by soil interception, but evident with foliar interception alone. Cell swelling in stems and in interveinal leaf lamina was observed after foliar application. A radiotracer study in redroot pigweed showed that only a small amount (3.3% of applied) of isoxaben entered the leaf following foliar application, and that little (0.08% of applied) isoxaben migrated beyond the point of application. The potential of isoxaben as a POST herbicide may be limited, in part, by poor absorption and translocation.

Field studies were conducted for 3 yr to determine weed and potato response to preemergence (PRE) and postemergence (POST) applications of rimsulfuron, metribuzin, and rimsulfuron plus metribuzin. Preemergence applications of rimsulfuron at 27 g ai/ha and POST applications at 18 g/ha controlled barnyardgrass, redroot pigweed, and wild buckwheat. Common lambsquarters was controlled by PRE or POST applications of metribuzin or a tank mixture of 18 g/ha rimsulfuron plus 140 g ai/ha of metribuzin. ‘Russet Burbank’ potato was relatively tolerant to all rimsulfuron, metribuzin, and rimsulfuron plus metribuzin applications, and potato yield was not reduced compared to the hand-weeded control.

Field experiments were conducted to compare performance of glyphosate with three different boom arrangements in a winter wheat-fallow rotation near North Platte, NE, in 1994 and 1995. One boom was optically controlled, and the other boom was for broadcast herbicide applications. Spraying with both booms at the same time was called “dual boom.” The sprayers were tested during May, June, and July on two weed density levels established by applying glyphosate at 0.42 kg ae/ha with and without atrazine at 0.84 kg ai/ha in October following wheat harvest. The dual-boom and the broadcast herbicide applications were more efficient in controlling weeds than the optically controlled system. The dual boom reduced weed density 4.5-fold compared with the optically controlled sprayer used alone. Horseweed < 8 cm tall was more difficult to control with the optically controlled sprayer than redroot pigweed and kochia because of its cylindrical-shaped growth patterns. Barnyardgrass and green foxtail seedlings with an erect growth pattern were also difficult for the sensors to detect. Poorer control with the optically controlled sprayer was associated with failure to identify small weeds, chlorotic plants, inconsistency among sensors, and too wide a field of view (FOV), as sensors were spaced farther apart than presently recommended. The number of sensors on a boom needs to be increased to improve the performance of the optically controlled sprayer.

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.

A weed survey system methodology was developed and used annually for 4 yr in the province of Saskatchewan. Based on a stratified random sampling procedure, fields were selected in wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), oat (Avena sativa L.), rye (Secale cereale L.), rape (Brassica napus L., Brassica campestris L.), and flax (Linum usitatissimum L.) crops. The boundaries of the 43 agricultural extension districts in the province formed the strata. The provincial agricultural extension service provided staff to conduct the survey. Computer processing of the data enabled reports, containing summary tables and distribution maps, to be distributed to extension, research, and industry personnel within 3 months after completion of the field survey. The field surveys were conducted late in the growing season before harvest commenced; hence, the weed populations consisted of species that had been present during the early part of the growing season and may have contributed to yield losses. During the 4 yr of the survey, weeds were counted in 4423 fields. Of the 164 species recorded, 97 species occurred in more than three fields. Only 29 species were encountered frequently in the fields. Green foxtail [Setaria viridis (L.) Beauv. # SETVI), wild buckwheat (Polygonum convolvulus L. # POLCO), and wild oat (Avena fatua L. # AVEFA) were the top three species based on a ranking system using a measure called relative abundance.

In field experiments, chlorsulfuron and CGA 131036 did not injure winter wheat. Both herbicides applied postemergence at 9 and 10 g ai/ha completely controlled flixweed. CGA 131036 controlled cutleaf eveningprimrose 81%, and chlorsulfuron controlled 91%. At similar rates, CGA 131036 was also less effective than chlorsulfuron on henbit and Italian ryegrass. Both controlled wild buckwheat 77% when applied postemergence at 18 g/ha. Neither of the sulfonylurea herbicides controlled prostrate spurge or woolly croton as effectively as 2,4-D. In a bean root bioassay, root growth inhibition by both herbicides was partially alleviated by adding isoleucine and valine.

A long-term study was conducted at Lethbridge, Alberta, to determine the response of weed populations to various crop rotations and tillage treatments. Weed density and species composition differed with rotation, tillage, and date of sampling within years. Fewer weeds were found in winter wheat-fallow than continuous winter wheat, winter wheat-lentil, or winter wheat-canola rotations. A dense infestation of downy brome developed in the continuous winter wheat rotation. In all rotations, more weeds were present in zero tillage plots than in either minimum or conventional tillage plots. Dandelion and perennial sowthistle densities increased slightly over years in the minimum and zero tillage treatments. Flixweed, field pennycress, wild buckwheat, and common lambsquarters densities decreased in zero till but densities of downy brome, redroot pigweed, and Russian thistle increased. Russian thistle was not well controlled with trifluralin and its density increased in the winter wheat-canola rotation.

A curved-linear Fresnel lens was investigated to test the effect of concentrated solar radiation on surface and buried weed seed. The lens produced a line focus 1 by 150 cm with a mean temperature of 309 C. A 20-s exposure to seed on the soil surface was 100% lethal to green foxtail, kochia, common lambsquarters, common purslane, and wild buckwheat. In a separate study, emergence from kochia and yellow foxtail seed was reduced 100% at 10 mm soil depth after 15 min in soil of 35 and 93 g/kg moisture and 20 to 40% at 178 g/kg moisture content. Concentrated solar radiation from a Fresnel lens has the greatest potential for affecting weed seed on the soil surface. A series of Fresnel lenses and/or larger lenses may be required for many practical field applications.

Field experiments were initiated at Alliance and Hairy Hill, Alberta, in 1989 to investigate the effects of conventional tillage, zero tillage, and four levels of nitrogen fertilizer on continuous barley production. In both tillage systems, the nitrogen was banded 6 to 8 cm deep between alternate barley rows. Herbicides were used for weed control each year. The influence of tillage and nitrogen on weed seed population dynamics was determined in 1991 and 1992. In the zero-tillage system, a large proportion of the weed seeds were present either at the soil surface or at the 5- to 10-cm depth. Green foxtail, the dominant species at Alliance, was also present at Hairy Hill where field pennycress was dominant. Green foxtail was consistently associated with low (residual) nitrogen and, in most cases, with conventional tillage. At both locations, green foxtail populations tended to decrease to very low levels as nitrogen rate increased, especially in zero tillage. At Hairy Hill, field pennycress populations in the soil seedbank were higher in zero tillage compared with conventional tillage, but plants that emerged from the soil seedbank in the field in spring were lower in zero tillage. Field pennycress populations were highest under low nitrogen. The results indicate that banding nitrogen has the potential to be an effective tool for green foxtail and field pennycress management in conventional- and zero-tillage systems, resulting in less dependence on herbicides for their control.

In the field, eight barley (Hordeum vulgare L.) cultivars tolerated postemergence applications of AC 222,293 [a mixture of methyl 6 and 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) m- and p-toluate] at 0.4 to 1.4 kg/ha. AC 222,293 at 0.4 kg ai/ha applied at the 1.5- to 2-leaf stage controlled wild oats (Avena fatua L. # AVEFA) 96%, whereas 0.7 kg/ha applied at the 3.5- to 4-leaf stage controlled wild oats only 93%. Sugarbeets (Beta vulgaris L.) but not alfalfa (Medicago sativa L.), corn (Zea mays L.), pinto beans (Phaseolus vulgaris L.), or sunflower (Helianthus annus L.), were injured when planted 6 to 8 months after fall applications of AC 222,293 at 0.4 to 1.1 kg/ha.

The efficacy of reduced rates of POST herbicides for weed control in sweet corn was evaluated over a three-year period in field studies conducted at the Horticultural Experiment Station, Simcoe, Ontario. POST applications of metolachlor/cyanazine, cyanazine/atrazine and metolachlor/atrazine at 1/2X and 1/4X of labelled rates controlled broadleaf weeds comparable to that of standard labelled rates. Control exceeded 94% each year. Annual grass control was reduced with below-label rates, especially for cyanazine/atrazine and metolachlor/atrazine. A 1/2X application of nicosulfuron/rimsulfuron, following the 1/4X rate of cyanazine/atrazine, significantly improved grass control, compared to cyanazine/atrazine applied alone. Below-label rates did not result in decreased sweet corn yields.

Producers in the northern Great Plains are exploring alternative crop rotations, with the goal of replacing spring wheat-fallow. We characterized the weed associations occurring with tillage system and nitrogen level in two rotations, spring wheat (SW)-fallow (F) and SW-winter wheat (WW)-sunflower (SUN). Weed density was measured 10 yr after initiation of the study. With both rotations, weed community density was highest with no-till. For SW-F, green foxtail, yellow foxtail, and fairy candelabra comprised 99% of the weed community, whereas 13 species were observed in SW-WW-SUN. Fairy candelabra, a rangeland species, was observed only in the no-till system of SW-F. In SW-WW-SUN, no-till favored kochia, Russian thistle, and foxtails, whereas common lambsquarters and annual sowthistle were more common in tilled systems. Nitrogen fertilizer increased crop competitiveness in SW-WW-SUN with no-till, subsequently reducing weed density. Cultural strategies that disrupt weed associations will aid producers in managing weeds.

Generalizations concerning the effects of management practices on weed community dynamics often lack robustness, most likely because of the concomitant effects of agronomic and environmental factors. However, such generalizations, when valid, provide useful grounds for predictions and are thus desirable. This study attempted to evaluate the relative importance of crop rotation, tillage, and weed management as factors affecting weed communities and tested the hypothesis of an association between management practices and weeds from certain life cycle groups. Principal component analysis (PCA) of weed density data from a 4-yr field study conducted on a Kamouraska clay and a Saint-André gravelly sandy loam at La Pocatière QC, Canada, identified groups of weed species, while an analysis of variance (ANOVA) of PCA scores associated these groups with management factors. A multivariate analysis of variance (MANOVA) of regression coefficients describing time courses of density for each species confirmed treatment effects. Species segregated roughly according to life cycles. Interactions among weed management intensity, tillage, and crop rotation mostly explained species dominance in the various cropping systems. A first group of species, mostly annual dicots, largely dominated in minimum weed management treatments; their relative importance in each rotation varied with their level of susceptibility to postemergence herbicides. A second group included annuals and perennials, whose commonality seemed to be their tolerance to herbicides; these species also had a particular affinity for chisel and no-till treatments. A third group was formed by perennial species, each with a different response to tillage. The tenuous correspondence between commonly used classification schemes and management factors suggests that other aspects of weed biology (e.g., seed size, dispersal, production, germination requirements, and seedbank longevity) should be considered when trying to explain and predict the presence and dominance of certain weed species with regard to management practices.

2,4-D diethanolamine control of kochia was influenced by the source of water used as the spray carrier. Sodium bicarbonate in one water source related to the reduced kochia control. Sodium bicarbonate in a water spray carrier antagonized 2,4-D control of all plant species evaluated. Antagonism increased with the tolerance of a species to 2,4-D, concentration of sodium bicarbonate, and spray volume. Sodium bicarbonate antagonism of 2,4-D phytotoxicity was greatest with low temperature and relative humidity.

Differences in the depth of weed seedling recruitment due to agronomic management practices, such as reduced tillage, have implications for weed competitive ability and management strategies. Depth of seedling recruitment of Avena fatua, Triticum aestivum, Setaria viridis, Polygonum convolvulus, and Echinochloa crus-galli was measured in situ in 1997 and 1998 prior to seeding (preseeding) and before in-crop spraying (prespray) in a total of 44 zero-tillage and 44 conventional-tillage fields located across approximately 3 million ha of southern Manitoba, Canada. For the monocot species, depth of recruitment was measured from the soil surface to the intact seed coats, which marked the point of germination. For P. convolvulus, a dicot, greenhouse studies were conducted prior to sampling in the field to identify a reliable morphological marker indicating the point of germination. For all species, mean recruitment depth was found to be significantly shallower in zero- vs. conventional-tillage fields and significantly shallower in the preseeding vs. the prespray period. There were relatively few differences in mean recruitment depth among weed species. Within a sampling period and tillage system, for example, the greatest difference in mean recruitment depth between species was less than 1.2 cm, and the maximum mean recruitment depth across species, sampling times, and tillage practice was very shallow (less than 4.2 cm). Locating weed seedling recruitment depth is the first step in characterizing weed seedling recruitment microsites. Results indicate this information should be specific to tillage and sampling time.

A field study was conducted to determine the combined effects of row spacing, plant density, and herbicides on weed management and dry bean (Phaseolus vulgaris) yield. In weed-free dry bean, a reduction in row spacing from 69 to 23 cm increased yield by 19% and an increase in density from 20 to 50 plants/m2 increased yield by 17%. In the presence of weeds, narrow rows and high plant densities increased dry bean yield, but without herbicides, yields remained low. However, when combined with herbicides, narrow-row and high-density production practices resulted in better weed control and higher dry bean yield than that attained in a wide-row and low-density production system. Herbicide combinations, often at reduced rates, controlled weeds as well or better than the full rate of any individual herbicide. Ethalfluralin applied preplant incorporated followed by reduced rates of imazethapyr or bentazon postemergence (POST) consistently controlled weeds. Imazamox exhibited the potential to provide a total POST weed control option in dry bean production. Information gained in this study will be used to develop improved weed management programs appropriate for either wide- or narrow-row dry bean production systems.