Daniel C. Brainard

Weed suppression in a broccoli–winter rye intercropping system

Abstract Interseeded cover crops have the potential to maintain and improve soil quality, reduce the incidence of insect pests, and suppress weeds in vegetable production systems. However, the successful use of interseeded cover crops has been limited by their tendency to either inadequately suppress weeds or suppress both weeds and the crop. We hypothesized that in irrigated broccoli production, winter rye could suppress annual weeds through rapid emergence and shading, without adversely affecting the taller transplanted broccoli crop. In field experiments conducted in New York from 1999–2001, broccoli was cultivated at 0, 10, or 10 and 20 d after broccoli transplanting (DAT), with or without rye at the final cultivation. Rye interseeded at 0 DAT suppressed weeds and improved yields relative to unweeded controls but resulted in broccoli yield losses relative to weed-free controls in 2 of 3 years. Rye seeded at either 10 or 20 DAT did not reduce broccoli yields but had little effect on weeds for a given level of cultivation and resulted in Powell amaranth seed production of up to 28,000 seeds m−2. Rye interseeded at 0 DAT reduced light availability to weeds in 2000 but not in 2001 when Powell amaranth avoided shading from rye through rapid emergence and vertical growth. In greenhouse pot experiments, low temperatures for 7 d after seeding delayed the emergence of Powell amaranth by 3 d relative to rye and increased the suppression of Powell amaranth by rye from 61 to 85%. Our results suggest that winter rye may be more successfully integrated into broccoli production (1) when sown at higher densities, (2) in locations or seasons (e.g., spring) with lower initial temperatures, and (3) in combination with other weed management tools. Nomenclature: Powell amaranth = green pigweed, Amaranthus powellii S. Wats. AMAPO; broccoli, Brassica oleracea L. var. italica PLENCK ‘marathon’; winter rye, Secale cereale L.

Suppression of Powell Amaranth (Amaranthus powellii) by Buckwheat Residues: Role of Allelopathy

Abstract Previous studies have demonstrated that emergence and growth of Powell amaranth is inhibited in soils where buckwheat has been grown and incorporated. The primary objectives of this research were to (1) evaluate the possible role of allelopathy in explaining that suppression; (2) distinguish between suppression caused by incorporation of fresh buckwheat residues from suppression caused by changes in soil during buckwheat growth; and (3) quantify the relative importance of buckwheat root vs. shoot tissues in suppression. When all buckwheat plant parts were removed from soil in which buckwheat was grown, Powell amaranth emergence was not suppressed, but growth was reduced 70% compared to bare soil. Addition of buckwheat shoots, but not roots to these soils reduced emergence by 80%, and contributed to additional reduction in growth. Addition of chemically activated carbon did not increase emergence or growth in buckwheat-amended soil. However, thermally activated carbon resulted in greater adsorption of phenolics than chemically activated carbon and alleviated suppression of Powell amaranth in buckwheat-amended, high organic-matter soils. However, suppression was not overcome on mineral soils. In addition to adsorbing phenolics, activated carbon changed the nitrogen (N) content and electrical conductivity of soil extracts. Aqueous shoot extracts of buckwheat stimulated Powell amaranth germination slightly, but inhibited radicle growth. Aqueous soil extracts from buckwheat-amended soil inhibited germination of Powell amaranth compared with extracts from unamended soil. Results suggest that emergence suppression of Powell amaranth by buckwheat residues might be due to allelopathic compounds concentrated in the shoot tissues. However, these inhibitory effects appear to depend on interactions of buckwheat residues with soils. In contrast, suppression of growth of Powell amaranth appears to be associated primarily with lower N availability in buckwheat-grown soils. Nomenclature: Powell amaranth (= green pigweed), Amaranthus powellii S. Wats. AMAPO; buckwheat, Fagopyrum esculentum Moench

Survival and performance of the invasive vine Vincetoxicum rossicum (Apocynaceae) from seeds of different embryo number under two light environments.

The nonnative vine Vincetoxicum rossicum threatens several ecosystems in the Lower Great Lakes Basin of North America. One feature that may contribute to its invasiveness is the production of some seeds with multiple embryos (polyembryony), which may be beneficial as a bet-hedging strategy in variable environments. However, lower seed reserves per embryo in polyembryonic seeds may entail costs in low-light environments. The effect of seed from three embryonic classes (1, 2, or 3 embryos/seed) on V. rossicum survival and growth was studied under two forest understory light environments: full canopy (shade) or canopy gaps (light) in New York state. Two seedling cohorts were planted, in May 2004 and in May 2005. The survival and growth of seedlings was monitored biweekly for two (2005 cohort) or three (2004 cohort) seasons. For both cohorts, plants grown in canopy shade had reduced survival and growth compared with those grown in gaps. Contrary to expectations, seed embryo number had no effect on the final height, survival, or dry mass of plants in either habitat. Our results suggest that any fitness advantage provided by polyembryony may be habitat (light) dependent and not a general trait that affords V. rossicum a benefit in all habitats colonized.

Weed Management Strategies to Reduce Herbicide Use in Zero-Till Rice–Wheat Cropping Systems of the Indo-Gangetic Plains

Abstract In the rice–wheat (RW) systems of the Indo-Gangetic Plains of South Asia, conservation tillage practices, including zero-tillage (ZT), are being promoted to address emerging problems such as (1) shortages of labor and water, (2) declining factor productivity, (3) deterioration of soil health, and (4) climate change. Despite multiple benefits of ZT, weed control remains a major challenge to adoption, resulting in more dependence on herbicides for weed control. Alternative management strategies are needed to reduce dependence on herbicides and minimize risks associated with their overuse, including evolution of herbicide resistance. The objectives of this review are to (1) highlight and synthesize research efforts in nonchemical weed management in ZT RW systems and (2) identify future weed ecology and management research needs to facilitate successful adoption of these systems. In ZT RW systems, crop residue can play a central role in suppressing weeds through mulch effects on emergence and seed predation. In ZT rice, wheat residue mulch (5 t ha−1) reduced weed density by 22 to 76% and promoted predation of RW weeds, including littleseed canarygrass and barnyardgrass seeds. For ZT wheat, rice residue mulch (6 to 10 t ha−1) in combination with early sowing reduced emergence of littleseed canarygrass by over 80%. Other promising nonchemical approaches that can be useful in suppressing weeds in ZT RW systems include use of certified seeds, weed-competitive cultivars, stale seedbed practices, living mulches (e.g., sesbania coculture), and water and nutrient management practices that shift weed–crop competition in favor of the crop. However, more research on emergence characteristics and mulching effects of different crop residues on key weeds under ZT, cover cropping, and breeding crops for weed suppression will strengthen nonchemical weed management programs. Efforts are needed to integrate multiple tactics and to evaluate long-term effects of nonchemical weed management practices on RW cropping system sustainability. Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv.; littleseed canarygrass, Phalaris minor Retz.; sesbania, Oryza sativa L.; wheat, Triticum aestivum L. Resumen En sistemas de arroz-trigo (RW) de las planicies Indo-Gangéticas del sur de Asia, se está promoviendo el uso de prácticas de labranza de conservación, incluyendo labranza cero (ZT), para solucionar problemas emergentes tales como (1) escasez de agua y mano de obra, (2) reducción de productividad, (3) deterioro en la salud del suelo, y (4) cambio climático. A pesar de los múltiples beneficios de ZT, el control de malezas continúa siendo uno de los mayores retos para la adopción de esta tecnología, lo que resulta en una mayor dependencia en herbicidas para el control de malezas. Se necesitan estrategias alternativas de manejo para reducir la dependencia en herbicidas y minimizar los riesgos asociados a su sobreuso, incluyendo la evolución de resistencia a herbicidas. Los objetivos de esta revisión son (1) resumir y resaltar los esfuerzos de investigación en el manejo no-químico de malezas en sistemas ZT RW e (2) identificar las necesidades futuras de investigación sobre ecología y manejo de malezas para facilitar el éxito en la adopción de estos sistemas. En sistemas ZT RW, el residuo del cultivo puede jugar un rol central en la supresión de malezas mediante efectos de cobertura sobre la emergencia y la depredación de semillas. En arroz ZT, la cobertura con residuos de trigo (5 t ha−1) redujo la densidad de malezas 22 a 76% y promovió la depredación de malezas de RW, incluyendo semillas de Phalaris minor y Echinochloa crus-galli. Para trigo RW, la cobertura con residuos de trigo (6 a 10 t ha−1) en combinación con siembra temprana redujo la emergencia de P. minor en más de 80%. Otras estrategias no-químicas promisorias que pueden ser útiles para suprimir malezas en sistemas ZT RW incluyen el uso de semilla certificada, el uso de cultivares competitivos contra las malezas, y prácticas de siembra retrasada, coberturas vivas (e.g. Sesbania rostrata como co-cultivo), prácticas de manejo de agua y nutrientes que cambien la relación de competencia maleza-cultivo en favor del cultivo. Sin embargo, más investigación sobre características de emergencia y efectos de diferentes residuos de cultivos como coberturas sobre especies clave en ZT, coberturas vivas y mejoramiento genético de los cultivos para supresión de malezas fortalecerá los programas de manejo no-químico de malezas. Se necesitan esfuerzos para integrar múltiples tácticas y para evaluar los efectos en el largo plazo de las prácticas no-químicas de manejo de malezas sobre la sostenibilidad de sistemas de cultivos RW.

Winter Annual Weed Suppression in Rye–Vetch Cover Crop Mixtures

Abstract Winter annual weeds can interfere directly with crops and serve as alternative hosts for important pests, particularly in reduced tillage systems. Field experiments were conducted on loamy sand soils at two sites in Holt, MI, between 2008 and 2011 to evaluate the relative effects of cereal rye, hairy vetch, and rye–vetch mixture cover crops on the biomass and density of winter annual weed communities. All cover crop treatments significantly reduced total weed biomass compared with a no-cover-crop control, with suppression ranging from 71 to 91% for vetch to 95 to 98% for rye. In all trials, the density of nonmustard family broadleaf weeds was either not suppressed or suppressed equally by all cover crop treatments. In contrast, the density of mustard family weed species was suppressed more by rye and rye–vetch mixtures than by vetch. Cover crops were more consistently suppressive of weed dry weight per plant than of weed density, with rye-containing cover crops generally more suppressive than vetch. Overall, rye was most effective at suppressing winter annual weeds; however, rye–vetch mixtures can match the level of control achieved by rye, in addition to providing a potential source of fixed nitrogen for subsequent cash crops. Nomenclature: Cereal rye, Secale cereale L.; hairy vetch, Vicia villosa Roth; mustard family, Brassicaceae Resumen Las malezas anuales de invierno pueden interferir directamente con los cultivos y pueden servir como hospederos alternativos para plagas importantes, particularmente en sistemas con labranza reducida. Se realizaron experimentos de campo en suelos areno limosos en dos sitios en Holt, Michigan entre 2008 y 2011 para evaluar los efectos relativos de los cultivos de cobertura Secale cereale , Vicia villosa y la mezcla S. cereale-V. villosa sobre la biomasa y la densidad de las comunidades de malezas anuales de invierno. Todos los tratamientos de cultivos de cobertura redujeron significativamente la biomasa total de malezas en comparación con el testigo sin cultivo de cobertura, con una supresión que varió de 71 a 91% en el caso de V. villosa y de 95 a 98% en el caso de S. cereale. En todos los experimentos, la densidad de malezas de hoja ancha que no pertenecen a la familia de la mostaza (Brassicaceae) no fue suprimida o fue suprimida de la misma forma por todos los tratamientos de cobertura. En contraste, la densidad de la familia de la mostaza fue suprimida más por los tratamientos con S. cereale que el tratamiento de V. villosa. Los cultivos de cobertura fueron más consistentemente supresores del peso seco por individuo de malezas que de la densidad de malezas, y las coberturas que contenían S. cereale fueron más supresoras que la cobertura de V. villosa.

Suppression of Powell Amaranth (Amaranthus Powellii), Shepherd's-purse (Capsella Bursa-pastoris), and Corn Chamomile (Anthemis Arvensis) by Buckwheat Residues: Role of Nitrogen and Fungal Pathogens

Abstract Buckwheat residues can suppress both emergence and growth of weeds, but the mechanisms of this suppression are not well understood. The main objectives of this research were to evaluate the possible role of (1) low initial nitrogen (N) availability and (2) fungal pathogens in this suppression for three sensitive weed species: Powell amaranth, shepherds-purse, and corn chamomile. Growth chamber experiments were conducted comparing weed emergence and growth in bare soil or soil with freshly incorporated buckwheat residue at multiple rates of N fertilization with or without fungicide seed treatment. In the absence of N or fungicide addition, emergence of all weed species was reduced 40 to 70%, and dry weight was reduced 85% in buckwheat residue compared with bare soil. For all three weed species, suppression of growth by buckwheat residue was completely overcome with the addition of N. For shepherds-purse and corn chamomile (2005 only), suppression of emergence was also overcome with the addition of N. In 2006, treatment of corn chamomile seeds with fungicide resulted in a higher emergence in buckwheat residue than in bare soil. In contrast, suppression of Powell amaranth emergence was not overcome with N fertilization or fungicide treatment. The results suggest that buckwheat-mediated changes in N dynamics account entirely for suppression of weed growth but that the mechanisms responsible for suppression of emergence by buckwheat residue vary by species. Fungal and N effects account for suppression of emergence of corn chamomile and shepherds-purse, but the mechanism of suppression for Powell amaranth remains obscure. Nomenclature: Corn chamomile, Anthemis arvensis L. ANTAR; Powell amaranth  =  green pigweed, Amaranthus powellii S. Wats. AMAPO; shepherds-purse, Capsella bursa-pastoris (L.) Medicus CAPBP; buckwheat, Fagopyrum esculentum Moench

Weed Ecology and Nonchemical Management under Strip-Tillage: Implications for Northern U.S. Vegetable Cropping Systems

Abstract In northern U.S. vegetable cropping systems, attempts at no-till (NT) production have generally failed because of poor crop establishment and delayed crop maturity. Strip tillage (ST) minimizes these problems by targeting tillage to the zone where crops are planted while maintaining untilled zones between crop rows, which foster improvements in soil quality. ST has been shown to maintain crop yields while reducing energy use and protecting soils in vegetable crops, including sweet corn, winter squash, snap bean, carrot, and cole crops. Despite potential benefits of ST, weed management remains an important obstacle to widespread adoption. Increased adoption of ST in cropping systems for which effective, low-cost herbicides are either limited (e.g., most vegetable crops) or prohibited (e.g., organic systems) will require integration of multiple cultural, biological, and mechanical approaches targeting weak points in weed life cycles. Weed population dynamics under ST are more complex than under either full-width, conventional tillage (CT) or NT because weed propagules—as well as factors influencing them—can move readily between zones. For example, the untilled zone in ST may provide a refuge for seed predators or a source of slowly mineralized nitrogen, which affects weed seed mortality and germination in the tilled zone. Greater understanding of such interzonal interactions may suggest manipulations to selectively suppress weeds while promoting crop growth in ST systems. Previous studies and recent experiences in ST vegetable cropping systems suggest a need to develop weed management strategies that target distinct zones while balancing crop and soil management tradeoffs. For example, in untilled zones, optimal management may consist of weed-suppressive cover crop mulching, combined with nitrogen exclusion and high-residue cultivation as needed. In contrast, weed management in the tilled zone may benefit from innovations in precision cultivation and flame-weeding technologies. These short-term strategies will benefit from longer-term approaches, including tillage-rotation, crop rotation, and cover cropping strategies, aimed at preventing seed production, promoting seed predation and decay, and preventing buildup of problematic perennial weeds. However, a concerted research effort focused on understanding weed populations as well as testing and refining integrated weed management strategies will be necessary before ST is likely to be widely adopted in vegetable cropping systems without increased reliance on herbicides. Nomenclature: Carrot, Daucus carota L.; cole crops, Brassica spp.; snap bean, Phaseolus vulgaris L.; sweet corn, Zea mays L.; winter squash, Cucurbita moschata Duchesne ex Poir. Resumen En los sistemas de cultivos de vegetales del norte de Estados Unidos, los intentos de producción con cero labranza (NT) generalmente han fallado debido a un establecimiento pobre y madurez tardía del cultivo. El cultivo en bandas (ST) minimiza estos problemas al enfocar la labranza en la zona donde los cultivos son plantados mientras que mantiene zonas sin labrar entre las líneas del cultivo, lo cual mejora la calidad del suelo. ST ha mostrado la capacidad de mantener el rendimiento del cultivo al tiempo que reduce el uso de energía y protege el suelo en cultivos de vegetales, incluyendo maíz dulce, calabacín de invierno, frijol común, zanahoria y coles. A pesar de los beneficios potenciales de ST, el manejo de malezas continúa siendo un obstáculo importante para su mayor adopción. El incremento en la adopción de ST en sistemas de cultivos para los cuales herbicidas efectivos y de bajo costo son, ya sea, limitados (e.g., mayoría de cultivos de vegetales) o prohibidos (e.g., sistemas orgánicos), requerirá la integración de múltiples estrategias culturales, biológicas, y mecánicas dirigidas a los puntos débiles en los ciclos de vida de las malezas. Las dinámicas de poblaciones de las malezas en ST son más complejas que en labranza de cobertura total, labranza convencional (CT) o NT, porque los propágulos de las malezas, además de los factores que los influencian, pueden moverse ampliamente entre zonas. Por ejemplo, la zona no labrada en ST podría proveer refugio para depredadores de semillas o podría ser una fuente de nitrógeno de lenta mineralización, los cuales afectan la mortalidad y la germinación de las semillas de las malezas en la zona labrada. Un mayor entendimiento de tales interacciones entre zonas podría sugerir manipulaciones para suprimir las malezas selectivamente mientras se promueve el crecimiento del cultivo en sistemas ST. Estudios previos y experiencias recientes en sistemas de cultivos de vegetales en ST indican la necesidad de desarrollar estrategias de manejo de malezas que apuntan a zonas específicas mientras balancean los conflictos entre el manejo del cultivo y del suelo. Por ejemplo, en zonas sin labrar, el manejo óptimo podría consistir en usar cultivos de cobertura para la supresión de malezas, en combinación con la exclusión de nitrógeno y el uso del cultivo con altos residuos cuando sea necesario. En contraste, el manejo de malezas en la zona labrada podría beneficiarse de innovaciones en tecnología de cultivadores de precisión y de quemadores de llama. Estas estrategias de corto plazo se beneficiarán de estrategias de largo plazo orientadas a prevenir la producción de semillas, promover la depredación y degradación de semillas, y a prevenir el incremento de malezas perennes problemáticas. Sin embargo, un esfuerzo concertado de investigación enfocado no solo en entender las poblaciones de malezas, sino que en evaluar y refinar las estrategias integradas de malezas, será necesario antes de que ST sea ampliamente adoptada en sistemas de cultivos de vegetales sin una dependencia mayor en herbicidas.

Grass–Legume Mixtures and Soil Fertility Affect Cover Crop Performance and Weed Seed Production

Abstract Summer leguminous cover crops can improve soil health and reduce the economic and environmental costs associated with N fertilizers. However, adoption is often constrained by poor weed suppression compared to nonlegume cover crops. In field experiments conducted in organic vegetable cropping systems in north-central New York, two primary hypotheses were tested: (1) mixtures of legume cover crops (cowpea and soybean) with grasses (sorghum–sudangrass and Japanese millet) reduce weed seed production and increase cover crop productivity relative to legume monocultures and (2) higher soil fertility shifts the competitive outcome in favor of weeds and nonlegume cover crops. Cover crops were grown either alone or in grass–legume combinations with or without composted chicken manure. Under hot, dry conditions in 2005, cowpea and soybean cover crops were severely suppressed by weeds in monoculture and by sorghum–sudangrass in mixtures, resulting in low legume biomass, poor nodulation, and high levels of Powell amaranth seed production (> 25,000 seeds m−2). Under more typical temperature and rainfall conditions in 2006, cowpea mixtures with Japanese millet stimulated cowpea biomass production and nodulation compared to monoculture, but soybeans were suppressed in mixtures with both grasses. Composted chicken manure shifted competition in favor of weeds at the expense of cowpea (2005), stimulated weed and grass biomass production (2006), and suppressed nodulation of soybean (2006). In a complementary on-farm trial, cowpea mixtures with sorghum–sudangrass suppressed weed biomass by 99%; however, both common purslane and hairy galinsoga produced sufficient seeds (600 seeds m−2) to replenish the existing weed seedbank. Results suggest that (1) mixtures of cowpeas with grasses can improve nodulation, lower seed costs, and reduce the risk of weed seed production; (2) soybean is not compatible with grasses in mixture; and (3) future costs of weed seed production must be considered when determining optimal cover crop choices. Nomenclature: Common purslane, Portulaca oleracea L.; hairy galinsoga, Galinsoga ciliata (Ref.) Blake; Powell amaranth, Amaranthus powellii S. Wats; cowpea, Vigna unguiculata (L.) Walpers. ‘Red Ripper’; Japanese millet, Echinochloa frumentacea (Roxb.) Link; sorghum–sudangrass, Sorghum bicolor (L.) Moench × Sorghum sudanese (P.) Stapf, ‘Sweetleaf II’; soybean, Glycine max (L.) Merr.; buckwheat, Fagopyrum esculentum (L.) Moench.

Cultivation and interseeding for weed control in transplanted cabbage

Multiple means of overcoming interspecific competition between transplanted cabbage and interseeded cover crops were studied in field trials conducted from 1995 to 2001. Cover crop species and time of seeding (1995 and 1996), use of supplemental nitrogen (1997 and 1998), and herbicide regulation (1999 and 2001) were evaluated with the objective of integrating soil-improving cover crops into cabbage production while facilitating weed suppression with minimal use of herbicides. Cabbage was cultivated at 10, 10 + 20, or 10 + 20 + 30 d after transplanting (DAT) with or without cover crops (hairy vetch, lana vetch, or oats) sown at the time of the last cultivation. Early interseeding (10 DAT) of all species significantly reduced cabbage yields. Both vetches could be sown 20 or 30 DAT without a yield penalty. However, weed suppression was not consistently greater than cultivation without cover crops. Spring oats were unacceptably competitive, even when sown 30 DAT in some years. With additional nitrogen, cabbage yields were consistently increased, but the increases were not directly related to decreased competition from either weeds or cover crops. The potential for herbicide regulation of cover crops to prevent cabbage yield losses could not be evaluated because cabbage yields were not reduced by cover crops in 1999 and 2001. Although interseeded crops did not generally provide significant in-season weed suppression compared with cultivation alone, the lack of yield penalty and the potential soil-improving qualities of legumes may justify interseeding hairy vetch at 20 DAT in an integrated system. Nomenclature: Cabbage, Brassica oleracea L.; hairy vetch, Vicia villosa L.; lana vetch, Vicia dasycarpa L.; oats, Avena sativa L. Additional index words: Cover crops, cultivation, interseeding, interspecific competition, living mulches, smother crops. Abbreviation: DAT, days after transplanting.

Cover Crop Mulch and Weed Management Influence Arthropod Communities in Strip-Tilled Cabbage

ABSTRACT Cover crop mulch and weeds create habitat complexity in agricultural fields that may influence arthropods. Under strip-tillage systems, planting rows are tilled and preestablished cover crops can remain between rows. In field experiments conducted in Michigan in 2010 and 2011, a preestablished oat (Avena sativa L.) cover crop was allowed to grow between rows of strip-tilled cabbage and killed at 0, 9–14, or 21–27 d after transplanting (DAT). The effects of herbicide intensity and oat kill date on arthropods, weeds, and crop yield were examined. Two levels of herbicide intensity (low or high) were used to manipulate habitat vegetational complexity, with low weed management intensity resulting in more weeds, particularly in 2010. Oat kill date manipulated the amount of cover crop mulch on the soil surface. Later oat kill dates were associated with higher natural enemy abundance. Reduced herbicide intensity was associated with 1) lower abundance of several key cabbage (Brassica oleraceae L.) pests, and 2) greater abundance of important natural enemy species. Habitats with both later oat kill dates and reduced herbicide intensity contained 1) fewer herbivores with chewing feeding guilds and more specialized diet breadths, and 2) greater abundance of active hunting natural enemies. Oats reduced cabbage yield when oat kill was delayed past 9–14 DAT. Yields were reduced under low herbicide intensity treatments in 2010 when weed pressure was greatest. We suspect that increased habitat complexity associated with oat mulches and reduced herbicide intensity enhances biological control in cabbage, although caution should be taken to avoid reducing yields or enhancing hyperparasitism.