John T. O'Donovan

Wild Oat (Avena fatua) Interference in Barley (Hordeum vulgare) is Influenced by Barley Variety and Seeding Rate

Abstract: Field experiments were conducted at Vegreville and Lacombe, AB, to determine the influence of barley (Hordeum vulgare) variety and seeding rate on interference of wild oat (Avena fatua) with barley. Barley variety and seeding rate affected barley density, height at maturity, and seed yield, as well as wild oat shoot dry weight and seed yield in most experiments, but there was no variety by seeding rate interaction. As expected, the semidwarf varieties Falcon and CDC Earl were the shortest. Barley seedling emergence and subsequent plant densities varied among varieties, locations, and years. The hull-less varieties Falcon and CDC Dawn had the poorest emergence in most cases, whereas AC Lacombe and Seebe had the highest emergence. Wild oat shoot dry matter and seed production was highest in the Falcon, CDC Dawn, and CDC Earl plots, suggesting that these were the least competitive with wild oat. Barley yield loss from wild oat interference also tended to be highest in these varieties. Poor emergence of Falcon and CDC Dawn and the shorter stature of Falcon and CDC Earl likely contributed to their relatively poor competitiveness with wild oat. Increasing the seeding rate improved the competitiveness of all varieties, as evidenced by reduced wild oat shoot dry matter and seed production and, in some cases, improved barley yields. Nomenclature: Wild oat, Avena fatua L. #3 AVEFA; barley, Hordeum vulgare L. ‘Falcon’, ‘Phoenix’, ‘AC Lacombe’, ‘Seebe’, ‘CDC Earl’, ‘Harrington’, ‘CDC Dawn’. Additional index words: Hull-less barley, semidwarf barley, wild oat competition.

Recent Weed Control, Weed Management, and Integrated Weed Management

Abstract Integrated weed management (IWM) can be defined as a holistic approach to weed management that integrates different methods of weed control to provide the crop with an advantage over weeds. It is practiced globally at varying levels of adoption from farm to farm. IWM has the potential to restrict weed populations to manageable levels, reduce the environmental impact of individual weed management practices, increase cropping system sustainability, and reduce selection pressure for weed resistance to herbicides. There is some debate as to whether simple herbicidal weed control programs have now shifted to more diverse IWM cropping systems. Given the rapid evolution and spread of herbicide-resistant weeds and their negative consequences, one might predict that IWM research would currently be a prominent activity among weed scientists. Here we examine the level of research activity dedicated to weed control techniques and the assemblage of IWM techniques in cropping systems as evidenced by scientific paper publications from 1995 to June 1, 2012. Authors from the United States have published more weed and IWM-related articles than authors from any other country. When IWM articles were weighted as a proportion of country population, arable land, or crop production, authors from Switzerland, the Netherlands, New Zealand, Australia, and Canada were most prominent. Considerable evidence exists that research on nonherbicidal weed management strategies as well as strategies that integrate other weed management systems with herbicide use has increased. However, articles published on chemical control still eclipse any other weed management method. The latter emphasis continues to retard the development of weed science as a balanced discipline. Resumen El manejo integrado de malezas (IWM) puede ser definido como un enfoque holístico del manejo de malezas que integra diferentes métodos de control para brindar al cultivo una ventaja sobre las malezas. Esto es practicado globalmente con niveles de adopción que varían de finca a finca. El IWM tiene el potencial de restringir las poblaciones de malezas a niveles manejables, reducir el impacto ambiental de prácticas individuales de manejo de malezas, incrementar la sostenibilidad de los sistemas de cultivos y reducir la presión de selección sobre la resistencia a herbicidas de las malezas. Existe cierto debate acerca de si programas de control de malezas basados simplemente en herbicidas, ahora se han convertido a sistemas de cultivos con IWM más diversos. Dada la rápida evolución y dispersión de malezas resistentes a herbicidas y sus consecuencias negativas, uno podría predecir que la investigación en IWM sería actualmente una actividad prominente entre científicos de malezas. Aquí examinamos el nivel de actividad investigativa dedicada a técnicas de control de malezas y al ensamblaje de técnicas de IWM en sistemas de cultivos, usando como evidencia la publicación de artículos científicos desde 1995 al 1 de Junio, 2012. Autores de los Estados Unidos han publicado más artículos relacionados a malezas y a IWM que autores de cualquier otro país. Cuando se ajustó el peso de los artículos de IWM como proporción de la población del país, tierras arables o producción de cultivos, autores de Suiza, Holanda, Nueva Zelanda, Australia y Canadá fueron los más prominentes. Existe considerable evidencia de que ha incrementado la investigación sobre estrategias no-herbicidas de manejo de malezas y también sobre las estrategias que integran otros sistemas de manejo de malezas con el uso de herbicidas. Sin embargo, los artículos publicados sobre control químico todavía eclipsan cualquier otro método de manejo de malezas. Este último énfasis continúa retrasando el desarrollo de la ciencia de malezas como una disciplina balanceada.

Barley seeding rate influences the effects of variable herbicide rates on wild oat

Abstract Field experiments were conducted at Vegreville, Alberta, in 1997, 1998, and 1999 and in Lacombe, Alberta, in 1997 and 1998, to determine if barley row spacing (20 and 30 cm) and seeding rate (75, 125, and 175 kg ha−1) influenced the effects of variable tralkoxydim rates on barley seed yield, net economic returns, and wild oat seed production. In most cases, barley seed yield was unaffected by row spacing or seeding rate. Where no herbicide was applied, the presence of wild oat reduced barley yield at each location each year. When the herbicide was applied at 50, 75, or 100% of the recommended rate, barley yields were not affected by the presence of wild oat. Results were more variable at 25% of the recommended rate, especially at Lacombe, where yield losses occurred both years at this rate. The lowest net economic returns consistently occurred in the absence of herbicide application; however, the influence of herbicide rate on net returns varied among years and locations. Net returns were either higher at the lower herbicide rates or were unaffected by herbicide rate. Seeding rate and herbicide rate affected wild oat seed production at each location each year and also the amount of seeds in the soil seedbank at Vegreville in 1999. Row spacing had little or no effect on wild oat seed production. There was a consistent and highly significant seeding rate by herbicide rate interaction on wild oat seed production. The effects of tralkoxydim on wild oat seed production, especially at relatively low rates, were superior at the higher barley seeding rates. The results suggest that seeding barley at relatively high rates can result in optimum barley yields, undiminished economic returns, and effective wild oat management when tralkoxydim is used at lower than recommended rates. Nomenclature: Bromoxynil; glyphosate; MCPA; tralkoxydim; barley, ‘Falcon’, Hordeum vulgare L.; wild oat, Avena fatua L. AVEFA.

Ongoing Development of Integrated Weed Management Systems on the Canadian Prairies

Abstract Herbicides are very effective tools to control weeds but there has been an overreliance on their use at the expense of other useful methods of weed management. Farmers are interested in alternative methods of weed management but are concerned about the risk of adopting such practices with current small profit margins. Research on the Canadian Prairies has found that cropping systems that utilize zero tillage, diverse crop rotations, competitive cultivars, higher crop seed rates, specific fertilizer management, and cover crops can effectively manage weed populations, especially when used in conjunction with targeted but limited use of herbicides. Farmers are gaining confidence in the merits of such agronomic practices in terms of sustainable weed management and are gradually adopting these integrated cropping systems on their farms. Further research and extension efforts are required to ensure that these integrated weed management systems are biologically and economically robust to facilitate greater adoption at the farm level.

Effect of barley plant density on wild oat interference, shoot biomass and seed yield under zero tillage.

There has been little research aimed at developing regression models to describe the effects of barley and wild oat plant density on barley yield loss, or wild oat biomass and seed yield. Such models are an important component of integrated weed management systems, and can help determine when weed control with herbicides is economical. Field experiments were conducted over 4 yr at Vegreville, Alberta, to determine the interactive effects of wild oat and barley plant density on barley and wild oat variables in a zero tillage system. A nonlinear regression model in most cases provided good descriptions of barley yield loss, wild oat shoot dry weight, and wild oat seed yield as functions of wild oat and barley plant densities. The interactive effect of wild oat and barley plant density on percentage barley yield loss did not differ significantly (P = 0.05) among years. A pooled regression model describing barley yield loss accounted for 57% of the variation, and provides a means of estimating yield loss due ...

Integrating Cropping Systems with Cultural Techniques Augments Wild Oat (Avena fatua) Management in Barley

Abstract Wild oat causes more crop yield losses and accounts for more herbicide expenditures than any other weed species on the Canadian Prairies. A study was conducted from 2001 to 2005 at four Canadian Prairie locations to determine the influence of repeated cultural and herbicidal management practices on wild oat population density, biomass, and seed production, and on barley biomass and seed yield. Short or tall cultivars of barley were combined with normal or double barley seeding rates in continuous barley or a barley–canola–barley–field-pea rotation under three herbicide rate regimes. The same herbicide rate regime was applied to the same plots in all crops each year. In barley, cultivar type and seeding rate were also repeated on the same plots year after year. Optimal cultural practices (tall cultivars, double seeding rates, and crop rotation) reduced wild oat emergence, biomass, and seed production, and increased barley biomass and seed yield, especially at low herbicide rates. Wild oat seed production at the quarter herbicide rate was reduced by 91, 95, and 97% in 2001, 2003, and 2005, respectively, when tall barley cultivars at double seeding rates were rotated with canola and field pea (high management) compared to short barley cultivars at normal seeding rates continuously planted to barley (low management). Combinations of favorable cultural practices interacted synergistically to reduce wild oat emergence, biomass and seed production, and to increase barley yield. For example, at the quarter herbicide rate, wild oat biomass was reduced 2- to 3-, 6- to 7-, or 19-fold when optimal single, double, or triple treatments were combined, respectively. Barley yield reductions in the low-management scenario were somewhat compensated for by full herbicide rates. However, high management at low herbicide rates often produced more barley than low management in higher herbicide rate regimes. Nomenclature: Wild oat, Avena fatua L.; barley, Hordeum vulgare L.; canola, Brassica napus L.; field pea, Pisum sativum L.

Glyphosate Timing and Tillage System Effects on Glyphosate-Resistant Canola (Brassica napus)1

Glyphosate-resistant canola has been widely adopted in western Canada. This has prompted producer interest in the timing of glyphosate application, particularly under zero tillage, where glyphosate is often applied preseeding. Field experiments were conducted at Lacombe, Edmonton, and Beaverlodge in Alberta in 1997, 1998, and 1999 to determine the importance of preseeding glyphosate and the most effective growth stage to apply glyphosate to canola to optimize yield and weed management. Treatments consisted of zero-tillage systems, with and without preseeding glyphosate, and a conventional-tillage system involving preseeding tillage operations. Glyphosate was applied at the one- to two-, three- to four-, or five- to six-leaf stages of canola in each tillage system. Canola yield and weed dry weight were largely unaffected by the tillage system. In most instances, the highest canola yields occurred when glyphosate was applied early to the crop. The opposite occurred at Lacombe and Edmonton in 1999, however, where canola yield increased as glyphosate was applied at later crop growth stages. This yield benefit likely resulted from the control of late-emerging weeds that exerted competitive pressure on canola. Early glyphosate timing in glyphosate-resistant canola may eliminate the need for preseeding glyphosate in zero-tillage systems, and optimize yield and weed control. Nomenclature: Glyphosate; canola, Brassica napus L. ‘Quest’. Additional index words: Critical period of weed control, direct seeding, preseeding glyphosate application, reduced tillage, zero tillage.

Glyphosate-resistant wheat persistence in western Canadian cropping systems

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

Glyphosate-resistant spring wheat production system effects on weed communities

Abstract Glyphosate-resistant (GR) crops are produced over large areas in North America. A study was conducted at six western Canada research sites to determine seed date and tillage system effects on weed populations in GR spring wheat and canola cropping systems from 2000 to 2003. Four-year wheat–canola–wheat–pea rotations were devised with varying levels of GR crops in the rotation. Weed populations were determined at pre– and post–in-crop herbicide application intervals in 2000 and 2003. Early seeding led to higher and more variable in-crop wild oat and wild buckwheat populations. High frequencies of in-crop glyphosate wheat in the rotation usually improved weed management and reduced weed density and variability. Canonical discriminant analysis (CDA) across all locations revealed that by 2003, green foxtail, redroot pigweed, sowthistle spp., wild buckwheat, and wild oat, all associated with the rotation lacking in-crop glyphosate. Similar CDA analyses for individual locations indicated specific weeds were associated with 3 yr of in-crop glyphosate (Canada thistle at Brandon, henbit at Lacombe, and volunteer wheat, volunteer canola, and round-leaved mallow at Lethbridge). However, only henbit at Lacombe and volunteer wheat at Lethbridge occurred at significant densities. Although excellent weed control was attained in rotations containing a high frequency of GR crops, the merits of more integrated approaches to weed management and crop production should also be considered. Overall, rotations including GR spring wheat did not significantly increase short-term weed management risks in conventional tillage or low soil-disturbance direct-seeding systems. Nomenclature: Glyphosate; annual sowthistle, Sonchus oleraceus L. SONOL; Canada thistle, Cirsium arvense (L.) Scop. CIRAR; green foxtail, Setaria viridis (L.) Beauv. SETVI; henbit, Lamium amplexicaule L. LAMAM; perennial sowthistle, Sonchus arvensis L. SONAR; redroot pigweed, Amaranthus retroflexus L. AMARE; round-leaved mallow, Malva pusilla Sm.; spiny sowthistle, Sonchus asper (L.) Hill SONAS; wild buckwheat, Polygonum convolvulous L. POLCO; wild oat, Avena fatua L. AVEFA; canola, Brassica napus L.; pea, Pisum sativum L.; wheat, Triticum aestivum L.

Effect of Tillage on Weed Populations in Continuous Barley (Hordeum vulgare)1

Abstract: The influence of four tillage systems, varying from intensive to zero tillage, on weed populations and the vertical distribution of weed seeds in the soil was determined at Alliance, Hairy Hill, and Wainwright in northeastern Alberta. The soil was sampled at two depths (0 to 5 and 5 to 10 cm) in fall. Weed seedling emergence in the greenhouse over the winter was assumed to represent the type and amount of weed seeds present in the soil seedbank. Emerged weed seedlings were also identified and counted in the field in spring. In the zero-tillage system, most of the weed seeds were close to the soil surface (0 to 5 cm) at Alliance and Wainwright but were deeper (5 to 10 cm) at Hairy Hill. The winter annuals, field pennycress, shepherds-purse, and flixweed, and the summer annuals, wild buckwheat and common lambsquarters, increased in the soil seedbank as tillage was reduced, but the higher populations in the soil seedbank did not always result in higher spring seedling populations under zero tillage. In contrast to the seedbank, spring seedling populations of common lambsquarters at Alliance and field pennycress and ball mustard at Hairy Hill were lowest in the zero-tillage system, suggesting that the requirement for herbicides for controlling these weeds in the crop may be least under zero tillage. Both soil seedbank and spring seedling populations of shepherds-purse at Wainwright and Alliance and of flixweed at Alliance were highest in the zero-tillage system. At Alliance, wild buckwheat seedling emergence in the spring tended to be highest in the minimum-tillage system (one tillage operation prior to seeding). Both soil seedbank and spring seedling populations of green foxtail decreased as tillage was reduced, indicating that green foxtail should become less of a problem under reduced tillage. Nomenclature: Ball mustard, Neslia paniculata (L.) Desv. #3 NEAPA; common lambsquarters, Chenopodium album L. CHEAL; field pennycress, Thlaspi arvense L. THLAR; flixweed, Descurainia sophia (L.) Webb. ex Prantl. DESSO; green foxtail, Setaria viridis (L.) Beauv. SETVI; shepherds-purse, Capsella bursa-pastoris (L.) Medik. CAPBP; wild buckwheat, Polygonum convolvulus L. POLCO. Additional index words: Intensive tillage, moderate tillage, minimum tillage, zero tillage.