K. Neil Harker

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.

Weed-competitive ability of spring and winter cereals in the northern Great Plains.

Abstract The inclusion of winter cereals in spring-annual rotations in the northern Great Plains may reduce weed populations and herbicide requirements. A broad range of spring and winter cereals were compared for ability to suppress weeds and maximize grain yield at Lacombe (2002 to 2005) and Lethbridge (2003 to 2005), Alberta, Canada. High seeding rates (≥ 400 seeds/m2) were used in all years to maximize crop competitive ability. Spring cereals achieved high crop-plant densities (> 250 plants/m2) at most sites, but winter cereals had lower plant densities due to winterkill, particularly at Lethbridge in 2004. All winter cereals and spring barley were highly effective at reducing weed biomass at Lacombe for the first 3 yr of the study. Weed suppression was less consistently affected by winter cereals in the last year at Lacombe and at Lethbridge, primarily due to poor winter survival. Grain yields were highest for spring triticale and least for spring wheat at Lacombe, with winter cereals intermediate. At Lethbridge, winter cereals had higher grain yields in 2003 whereas spring cereals had higher yields in 2004 and 2005. Winter cereals were generally more effective at suppressing weed growth than spring cereals if a good crop stand was established, but overlap in weed-competitive ability among cultivars was considerable. This information will be used to enhance the sustainable production of winter and spring cereals in traditional and nontraditional agro-ecological zones.

Survey of yield losses due to weeds in central Alberta

Weedy and weed-free yields were determined in fields of barley, canola, and peas in Lacombe County, Alberta, Canada from 1995 to 1997. Yield losses were most frequent and severe in peas, and least frequent and less severe in barley. Yield losses due to weed competition were not detectable at 33, 60, and 73% of the pea, canola, and barley sites, respectively. Key words: Competition, interference, barley, canola, peas

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.

Timing Weed Removal in Field Pea (Pisum sativum)1

Abstract: Field experiments were conducted in 1996, 1997, and 1998 at Lacombe and Lethbridge, AB, to determine the influence of early weed competition on field pea yields. Wild oat and Tartary buckwheat were removed from plots at weekly intervals after pea emergence by hand-weeding and maintained weed-free for the remainder of the growing season. Tartary buckwheat produced slightly more biomass than wild oat at Lacombe, whereas wild oat produced much more biomass than Tartary buckwheat at Lethbridge. Weed-free pea yields at Lacombe were always two- to threefold higher than at Lethbridge. At Lethbridge, early competition with Tartary buckwheat in all years, and with wild oat in 1998, did not reduce pea yields. In 1996 and 1997 at Lethbridge, pea yield reductions due to wild oat began at 2 wk after pea emergence; for the next 2 wk yield loss was linear, decreasing at an average rate of 97 kg/ha per day. Early weed competition led to pea yield losses at Lacombe in all 3 yr. The onset of yield loss at Lacombe over the 3-yr period ranged from 1 to 2 wk after pea emergence; for the next 2 to 3 wk yield loss was linear, decreasing at an average rate of 45 kg/ha per day. Yield losses after full-season weed competition ranged from 40 to 70% at both sites. Usually, the beginning of the critical weed-free period was at 1 or 2 wk after pea emergence. Optimum pea yields usually required weed removal very early in the pea life cycle; weed removal beyond 2 wk after pea emergence often protected only suboptimal yields. Nomenclature: Wild oat, Avena fatua L. #3 AVEFA; Tartary buckwheat, Fagopyrum tataricum (L.) J. Gaertn.; pea, Pisum sativum L. Carrera. Additional index words: Critical weed-free period, crop-weed interference, duration of competition, AVEFA. Abbreviations: POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Integration of Agronomic Practices and Herbicides for Sustainable Weed Management in a Zero-Till Barley Field Pea Rotation1

Research is needed to develop more comprehensive integrated weed management systems that would facilitate greater adoption by farmers. A field study was conducted to determine the combined effects of seed date (April or May), seed rate (recommended or 150% of recommended), fertilizer timing (fall or spring applied), and in-crop herbicide rate (50 or 100% of recommended) on weed growth and crop yield. This factorial set of treatments was applied in four consecutive years within a barley-field pea–barley-field pea rotation in a zero-till production system. Both barley and field pea phases of the rotation were grown each year to account for variable environmental conditions over years. Weed biomass was often lower with May than with April seeding because of more weeds being controlled with preplant glyphosate. However, despite fewer weeds being present with May seeding, barley yield was only greater in 1 of 4 yr and field pea yield was actually lower with May than with April seeding in 3 of 4 yr, indicating that optimum seed date is highly dependent on crop species and environmental conditions. Higher crop seed rates reduced weed biomass and increased crop yield in 2 of 4 yr in each of barley and field pea. Fertilizer timing had little effect on weed competition in barley, but spring- compared with fall-applied fertilizer reduced weed biomass and increased field pea yield in 2 of 4 yr. In-crop herbicides applied at 50% compared with 100% rates sometimes resulted in greater weed biomass and lower crop yields with recommended crop seed rates, but few differences were noted at high crop seed rates. Indeed, the weed seed bank at the conclusion of the 4-yr study was not greater with the 50% compared with 100% herbicide rate when high crop seed rates were used. This study demonstrates the combined merits of early seeding (April), higher crop seed rates, and spring-applied fertilizer in conjunction with timely but limited herbicide use to manage weeds and maintain high yields in rotations containing barley and field pea. Nomenclature: Glyphosate; barley, Hordeum vulgare L. ‘AC Harper’; field pea, Pisum sativum L. ‘Swing’. Additional index words: Fertilizer timing, integrated weed management, reduced herbicide rate, seed date, seed rate, weed competition. Abbreviation: IWM, integrated weed management.