Weed community ecology : Tedious sampling or relevant science? A Canadian perspective

L'étude de l'écologie des communautés de mauvaises herbes implique des aspects de types d'espèces, de diversité et de variabilité spatiale et temporelle. Auparavant, la recherche canadienne dans ce secteur mettait l'accent sur les inventaires de mauvaises herbes, alors que la recherche a plus récemment porté sur la composition des communautés résultant des méthodes de travail du sol et des rotations. De nouvelles techniques d'analyse multivariée ont été utilisées afin d'analyser les mauvaises herbes à l'échelle de la communauté plutôt que celle de l'espèce, d'où une nouvelle compréhension de la dynamique des communautés. Quoique l'étude de l'écologie des communautés de mauvaises herbes implique souvent des échantillonnages laborieux, l'accroissement des efforts de recherche dans ce secteur devrait procurer les bases nécessaires au développement de stratégies efficaces de lutte intégrée contre les mauvaises herbes. Cet article présente les aspects de l'écologie des communautés de mauvaises herbes à la lumière de la recherche canadienne, et formule des recommandations pour de futures démarches de recherche.The study of weed community ecology involves aspects of species life forms, diversity, and spatial and temporal variability. Previously, Canadian research in this area focused on weed surveys, while recent research has been conducted on community composition as influenced by tillage System and crop rotation. New techniques in multivariate ordination have been used to analyse weeds at a community rather than a species level, with a resultant new understanding of community dynamics. Although the study of weed community ecology often involves tedious sampling, increased research in this area would provide the basis for the development of effective integrated weed management strategies. This paper discusses aspects of weed community ecology in light of Canadian research and makes recommendations for future studies

Herbicide injury in special crops from sprayer tank residues

Non-Peer ReviewedBroad-leaved special crops have long been known to be sensitive to phenoxy herbicides. Field trials were conducted on sunflowers, lentils and mustard. Simulated sprayer tank residues of 2, 1, 0.5, and 0.25 % of the field rate of the broad-leaved weed herbicides were applied alone and with diclofop-methyl and sethoxydim as they would be with the subsequent use of the sprayer in the special crops. The grassy weed herbicides enhanced the effect of 2,4-D, MCPA and dicamba in sunflowers and of clopyralid in lentils while the effect of chlorsulfuron alone in mustard equaled that of the grassy weed herbicide mixtures. Yields losses occurred in all three special crops from the simulated residues of herbicides used in cereal crops. losses ranged from 0 to 92 % depending on the herbicide combination, rate applied, and crop tested

The effects of preseeding 2,4-D and dicamba + 2,4-D application on subsequent crops

Non-Peer ReviewedThe development of reduced tillage systems and direct seeding systems require the use of herbicides in the fall and prior to seeding to control weeds. A study was initiated in 1988 at Indian Head to examine the effects of 2,4-D amine and 2,4-D amine + dicamba applied in the fall or spring prior to seeding on flax, safflower, mustard, canola, lentil and field pea. Herbicides were applied at the low, high,and double the high rates recommended for use in cereal crops (420, 560, and 1120 g/ha of 2,4-D; and 110 + 420, 140 + 420, and 280 + 840 g/ha of dicamba +2,4-D). Visual crop tolerance ratings, plant populations and yield were assessed in 1988 and 1989. In general, none of the crops tested were adversely affected by faII application of 2,4-D amine alone at up to 1120 g/ha. Spring application of 2,4-D amine alone at 560 and 1120 g/ha caused significant yield reductions in safflower and lentil in 1 out of 2 years but none of the other crops were affected by spring 2,4-D application in either year regardless of the rate. Dicamba + 2,4-D did not cause significant yield reductions in flax, canola or mustard, however, safflower, lentil and pea yields were significantly reduced by spring application of dicamba + 2,4-D regardless of rate and by all but the lowest rate (110 + 420 g/ha) of this mixture applied in the fall

Triasulfuron and chlorsulfuron persistence under zero and minimum tillage

Non-Peer Reviewe

Arbuscular mycorrhizal fungi influence competition between barley and wild oat

Non-Peer ReviewedArbuscular mycorrhizal fungi (AMF) are soil fungi that intimately associate with most crops and influence their productivity. This study determined (i) the mycorrhizal dependency of eight barley cultivars and (ii) whether barley competitiveness against wild oat was linked to its mycorrhizal dependency. Of the eight cultivars tested, Virden was the most dependent on AMF whereas CDC Earl was the least dependent; Earl and Virden were therefore evaluated for competitiveness against wild oat at weed density ratios of 1:0.5, 1;1, 1:2 and 1:4 with or without AMF. Regardless of the AMF treatment, the total shoot dry weight of both barley varieties decreased with increasing crop:weed ratio. Earl derived 32% less benefit than Virden at a crop:weed ratio of 1: 0.5, and at a crop:weed ratio of 1:1, the total shoot dry weight of wild oat competing against Virden was significantly lower than that of wild oat competing against Earl. Regardless of the crop:weed ratio, (i) both barley varieties responded positively to the AMF mixture, (ii) the total shoot dry weight of AMF-inoculated Virden was 13% higher than that of AMF-inoculated Earl, and (iii) the shoot dry matter ratio of barley:wild oat was greater for AMF-inoculated Virden than Earl. At crop: weed ratios of up to 1:1, AMF-inoculated Virden plants had significantly more total shoot biomass than uninoculated Virden, whereas this was not the case with Earl. In general, wild oat competing against AMF-inoculated Virden had the least shoot dry matter at all the crop:weed ratios compared to all other treatments. These results suggest that the highly mycorrhizal Virden appeared to be more competitive than Earl and indicates that barley competitiveness may be partially linked to its mycorrhizal dependency

Distribution, biology, and control of downy brome (Bromus tectorum L.) in southwestern Saskatchewan

Non-Peer ReviewedDowny brome was likely introduced near Maple Creek in 1960, and has since spread to infest parts of four Agricultural Extension Districts in southwestern Saskatchewan (Maple Creek, Leader, Swift Current, Shaunavon). By 1987, a total of 150 downy brome reports from 72 townships have been confirmed. During the first weed survey of annual crop fields infested with downy brome, 35 fields were visited and the kinds and numbers of weeds were identified according to standardized weed survey procedures. Downy brome density averaged 213 plants per square metre, and associated weeds were Japanese brome, flixweed, green foxtail, and wild buckwheat. Japanese brome was found in 5 fields, and was less abundant than downy brome in the area surveyed. Large numbers of downy brome seeds (50,000 seeds per square metre) were extracted from soil samples. Downy brome seeds buried in soil germinated more rapidly than those seeds on the soil surface. Most downy brome seeds (98 %) buried 2.5, 5.0, 10.0, or 20.0 cm in soil germinated or deteriorated within 3 months. However, a few seeds remained viable in the soil after 3 months. Research is in progress to determine the relative winter hardiness of downy brome and winter wheat, and to develop chemical control methods

Competitiveness-shifts from weeds to crops using arbuscular fungi

Non-Peer ReviewedArbuscular fungi (AF) colonize ca. 80% of terrestrial plant roots and typically improve their growth by enhancing nutrient uptake, reducing disease severity and/or imparting resistance to abiotic stress. Therefore, AF-colonized crop cultivars exhibit early vigor and superior growth compared to cultivars not colonized by AF. However, routine AF inoculation of crops is limited because of their obligate nature. Nevertheless, there are strategies that can be readily adopted by growers to exploit the indigenous AF community. Our project aimed at determining the relationship between the mycorrhizal dependency of crops and crop competitiveness against weeds. The mycorrhizal dependency of eight barley and eight wheat cultivars on an AF mixture resembling that of an indigenous AF community was evaluated in natural soil. There were significant differences between the cultivars in their response to AF. The most and least mycorrhizal cultivar (based on biomass) were evaluated for their competitiveness against wild oat at four crop:weed density levels (1:0.5; 1:1; 1:2; 1:4) in soil with and without the AF mixture. Results showed that the most AF dependent cultivar in both crops exhibited superior growth and competitiveness against wild oat up to a level of 1:1 crop:weed density. This confirms that mycorrhizal dependency is partially linked to crop competitiveness against weeds and that the choice of cultivar may be a strategy which can enhance crop competitiveness while reducing chemical herbicide use

Effects of tillage systems and crop rotations on soil water conservation, seedling establishment and crop production of a thin Black soil at Indian Head

Non-Peer ReviewedThe long term sustainability of agriculture for much of western Canada is dependent on the development of economically viable crop production systems that alleviate wind and water erosion. The systems required must be capable of making full use of the benefits of surface residues and standing stubble. A study was initiated in 1986 at Indian Head to examine the interactions of tillage systems and crop rotations on soil water conservation, soil characteristics, seedling establishment, crop production, plant diseases, weed populations, and production economics. Three four year rotations were then superimposed on the three tillage systems. Spring soil water under stubble conditions was significantly greater for the zero and minimum tillage than conventional tillage system for the 0-60 and 0-120 cm soil layer. Under fallow conditions, soil water conserved was similar for all three tillage systems. Seedling establishment, as measured by the number of plants emerged per meter square was similar for all crops and tillage systems. Plant development in spring wheat, as measured by Haun stage was not affected by tillage system. This implies that the perceived differences in soil temperature at seeding depth between the various tillage systems did not significantly delay plant emergence under zero and minimum tillage. Tillage system had a significant effect on grain production. Zero and minimum tillage out-yielded conventional tillage by 22 % for flax, 20 % for spring wheat on stubble and 8 % for field peas. There was no difference between tillage systems for winter wheat

Downy brome seed bank dynamics in southwestern Saskatchewan

Non-Peer ReviewedIn order to study downy brome seed bank dynamics, a burial experiment was established near Maple Creek in August 1987. Downy brome seed was buried at four depths (2.5 to 20 cm), and placed on the soil surface, in nylon mesh bags. Seed was exhumed at monthly intervals in the fall of 1987 and throughout the 1988 growing season. Seed germination in the field in the fall of 1987 was greatest from the buried seed (almost 50 %) while the surface seed exhibited little germination. This germination occurred in response to fall precipitation. Seed on the soil surface was not in contact with moist soil for a sufficient time to stimulate germination, so 80-90 % of this seed had not germinated by freeze-up in 1987. However the surface collected seed had germination of 34 % when transferred to an incubator in the laboratory, indicating environmentally induced dormancy in the field. There was little recruitment from the seed bank occurred in the spring of 1988 in spite of favorable moisture and temperature conditions. Seed on the soil surface remained viable until the 14th month but the buried seed at all depths had either germinated or deteriorated by the 9th month. This study was repeated in 1988, with similar results to date

Effects of tillage method and crop rotation on non-renewable energy use efficiency in the thin Black Soil Zone

Non-Peer ReviewedLow prices for cereal grains, coupled with changing government policies and programs, and increasing concerns about soil and environmental degradation are stimulating significant change in land use practices throughout western Canada. The adoption and use of diversified crop rotations, together with conservation tillage practices are becoming widely accepted. However, little is known about the impacts of these land use changes on the requirements for non-renewable energy inputs and on energy use efficiency. This study examines the effects of alternative tillage practices on nonrenewable energy inputs, energy output, and energy use efficiency for monoculture cereal, cereal-oilseed, and cereal-oilseed-pulse crop rotations in the Thin Black soil zone of Saskatchewan