Matthew R. Ryan

Navigating a Critical Juncture for Sustainable Weed Management

Agricultural weed management has become entrenched in a single tactic—herbicide—resistant crops—and needs greater emphasis on integrated practices that are sustainable over the long term. In response to the outbreak of glyphosate-resistant weeds, the seed and agrichemical industries are developing crops that are genetically modified to have combined resistance to glyphosate and synthetic auxin herbicides. This technology will allow these herbicides to be used over vastly expanded areas and will likely create three interrelated challenges for sustainable weed management. First, crops with stacked herbicide resistance are likely to increase the severity of resistant weeds. Second, these crops will facilitate a significant increase in herbicide use, with potential negative consequences for environmental quality. Finally, the short-term fix provided by the new traits will encourage continued neglect of public research and extension in integrated weed management. Here, we discuss the risks to sustainable agriculture from the new resistant crops and present alternatives for research and policy.

Conservation tillage issues: Cover crop-based organic rotational no-till grain production in the mid-Atlantic region, USA

Organic producers in the mid-Atlantic region of the USA are interested in reducing tillage, labor and time requirements for grain production. Cover crop-based, organic rotational no-till grain production is one approach to accomplish these goals. This approach is becoming more viable with advancements in a system for planting crops into cover crop residue flattened by a roller–crimper. However, inability to consistently control weeds, particularly perennial weeds, is a major constraint. Cover crop biomass can be increased by manipulating seeding rate, timing of planting and fertility to achieve levels(>8000kgha �1 ) necessary for suppressing summerannual weeds. However, while cover crops are multi-functional tools, when enhancing performance for a given function there are trade-off with other functions. While cover crop management is required for optimal system performance, integration into a crop rotation becomes a critical challenge to the overall success of the production system. Further, high levels of cover crop biomass can constrain crop establishment by reducing optimal seed placement, creating suitable habitat for seed- and seedling-feeding herbivores, and impeding placement of supplemental fertilizers. Multi-institutional and -disciplinary teams have been working in the mid-Atlantic region to address system constraints and management trade-off challenges. Here, we report on past and current research on cover crop-based organic rotational no-till grain production conducted in the mid-Atlantic region.

Overcoming weed management challenges in cover crop-based organic rotational no-till soybean production in the Eastern United States

Abstract Cover crop–based organic rotational no-till soybean production has attracted attention from farmers, researchers, and other agricultural professionals because of the ability of this new system to enhance soil conservation, reduce labor requirements, and decrease diesel fuel use compared to traditional organic production. This system is based on the use of cereal rye cover crops that are mechanically terminated with a roller-crimper to create in situ mulch that suppresses weeds and promotes soybean growth. In this paper, we report experiments that were conducted over the past decade in the eastern region of the United States on cover crop–based organic rotational no-till soybean production, and we outline current management strategies and future research needs. Our research has focused on maximizing cereal rye spring ground cover and biomass because of the crucial role this cover crop plays in weed suppression. Soil fertility and cereal rye sowing and termination timing affect biomass production, and these factors can be manipulated to achieve levels greater than 8,000 kg ha−1, a threshold identified for consistent suppression of annual weeds. Manipulating cereal rye seeding rate and seeding method also influences ground cover and weed suppression. In general, weed suppression is species-specific, with early emerging summer annual weeds (e.g., common ragweed), high weed seed bank densities (e.g. > 10,000 seeds m−2), and perennial weeds (e.g., yellow nutsedge) posing the greatest challenges. Due to the challenges with maximizing cereal rye weed suppression potential, we have also found high-residue cultivation to significantly improve weed control. In addition to cover crop and weed management, we have made progress with planting equipment and planting density for establishing soybean into a thick cover crop residue. Our current and future research will focus on integrated multitactic weed management, cultivar selection, insect pest suppression, and nitrogen management as part of a systems approach to advancing this new production system. Nomenclature: Common ragweed, Ambrosia artemisiifolia L.; yellow nutsedge, Cyperus esculentus L.; cereal rye, Secale cereale L.; corn, Zea mays L.; soybean, Glycine max (L). Merr.; wheat, Triticum aestivum L. Resumen La producción orgánica de soya en sistemas de rotación con cero labranza basados en cultivos de cobertura, ha atraído la atención de productores, investigadores y otros profesionales agrícolas por la habilidad de este nuevo sistema de mejorar la conservación del suelo, reducir los requerimientos de mano de obra y disminuir el uso de combustible diesel en comparación con la producción orgánica tradicional. Este sistema está basado en el uso de centeno como cultivo de cobertura el cual es terminado mecánicamente con un rodillo de cuchillas para crear una cobertura de residuos in situ que suprime malezas y promueve el crecimiento de la soya. En este artículo, reportamos experimentos que fueron realizados durante la década pasada en la región este de los Estados Unidos sobre la producción orgánica de soya en sistemas de rotación con cero labranza basados en cultivos de cobertura, y delineamos las estrategias actuales de manejo y las necesidades futuras de investigación. Nuestra investigación se ha enfocado en maximizar la cobertura y la biomasa del centeno de primavera debido al papel crucial que este cultivo de cobertura juega en la supresión de malezas. La fertilidad del suelo y el momento de siembra y término del centeno afectan la producción de biomasa, y estos factores pueden ser manipulados para alcanzar niveles mayores a 8,000 kg ha−1, el cual es el umbral identificado para la supresión consistente de malezas anuales. Manipular la densidad y métodos de siembra también influencia la cobertura del suelo y la supresión de malezas. En general, la supresión de malezas es específica a la especie, siendo las malezas anuales de verano que emergen temprano (e.g. Ambrosia artemisiifolia), los banco de semillas con altas densidades (e.g. >10,000 semillas m−2), y las malezas perennes (e.g. Cyperus esculentus) los mayores retos. Debido a los retos de maximizar el potencial de supresión de malezas del centeno, hemos encontrado que el cultivar con altos residuos también puede mejorar el control de malezas significativamente. Adicionalmente al cultivo de cobertura y el manejo de malezas, hemos progresado con el equipo y la densidad de siembra para el establecimiento de la soya en capas gruesas de residuos de cultivos de cobertura. Nuestra investigación actual y futura se centrará en el manejo integrado de malezas multitáctico, la selección de cultivares, la supresión de plagas insectiles, y el manejo del nitrógeno como parte de un enfoque de sistemas para el avance de este nuevo sistema de producción.

Energy Use and Greenhouse Gas Emissions from Crop Production Using the Farm Energy Analysis Tool

Using the Farm Energy Analysis Tool (FEAT), we compare energy use and greenhouse gas (GHG) emissions from the cultivation of different crops, highlight the role of sustainable management practices, and discuss the impact of soil nitrous oxide (N2O) emissions and the uncertainty associated with denitrification estimates in the northeastern United States. FEAT is a transparent, open-source model that allows users to choose parameter estimates from an evolving database. The results show that nitrogen fertilizer and N2O emissions accounted for the majority of differences between crop energy use and GHG emissions, respectively. Integrating sustainable practices such as no tillage and a legume cover crop reduced energy use and GHG emissions from corn production by 37% and 42%, respectively. Our comparisons of diverse crops and management practices illustrate important trade-offs and can inform decisions about agriculture. We also compared methods of estimating N2O emissions and suggest additional research on this potent GHG.

Management Filters and Species Traits: Weed Community Assembly in Long-Term Organic and Conventional Systems

Abstract Community assembly theory provides a useful framework to assess the response of weed communities to agricultural management systems and to improve the predictive power of weed science. Under this framework, weed community assembly is constrained by abiotic and biotic “filters” that act on species traits to determine community composition. We used an assembly approach to investigate the response of weed seed banks to 25 yr of management-related filtering in three different row-crop management systems in southeastern Pennsylvania: organic manure-based, organic legume-based, and conventional. Weed seed banks were sampled in April of 2005 and 2006 and quantified by direct germination in a greenhouse. We also assessed the filtering effects of weed management practices and relationships between assembled seed bank and emergent weed communities by allowing or excluding weed control practices within each management system and measuring emergent weed community response. Germinable weed seed bank densities and species richness in the final year of the study were over 40% and 15% higher, respectively, in the organic systems relative to the conventional system. Seed bank community structure in the organic systems was different from the conventional system, and the relationships between assembled seed banks and the emergent flora varied. Primary tillage, weed control, timing of planting, and fertility management appeared to be the main filters that differentiated weed seed banks in the three systems. Weed life history, emergence periodicity, seed size, and responsiveness to soil fertility and hydrology appeared to be the most important functional traits determining how weed species responded to management-related filters. Our results suggest that management systems can exert strong filtering effects that can persist over relatively long (greater than one growing season) time scales. Legacy effects of community-level filtering might be more important than previously assumed, and should be incorporated into predictive models of weed community assembly.

Potential Synergistic Effects of Cereal Rye Biomass and Soybean Planting Density on Weed Suppression

Increasing crop density is a cultural weed management practice that can compliment the use of cover crops for weed suppression. In this research, we created a range of cover crop biomass and soybean densities to assess their weed-suppressive ability alone and in combination. The experiment was conducted in 2008 and 2009 in Maryland and Pennsylvania using five levels of cereal rye residue, representing 0, 0.5, 1.0, 1.5, and 2.0 times the ambient level, and five soybean densities ranging from 0 to 74 seeds m−2. Weed biomass decreased with increasing rye residue and weeds were completely suppressed at levels above 1,500 g m−2. Weed biomass also decreased with increasing soybean density in 2 of 4 site–years. We evaluated weed suppression by fitting an exponential decay model of weed biomass as a function of rye biomass and a hyperbolic model of weed biomass as a function of soybean density at each of the five tactic levels. We multiplied these individual tactic models and included an interaction term to test for tactic interactions. In two of the four site-years, the combination of these tactics produced a synergistic interaction that resulted in greater weed suppression than would be predicted by the efficacy of each tactic alone. Our results indicate that increasing soybean planting rate can compensate for lower cereal rye biomass levels when these tactics are combined. Nomenclature: Cereal rye, Secale cereale L.; soybean, Glycine max (L.) Merr

Cover Crops and Disturbance Influence Activity-Density of Weed Seed Predators Amara aenea and Harpalus pensylvanicus (Coleoptera: Carabidae)

The activity-density of Amara aenea (DeGeer) and Harpalus pensylvanicus (DeGeer) (Coleoptera: Carabidae) was monitored in an experiment that compared five management treatments representing a range of disturbance frequencies, crops, and aboveground biomass production. In 2004 and 2005, three treatments comprised of multiple summer cover crops were compared to bare fallow and soybean, the latter of which used mechanical cultivation to manage weeds. In 2005 weed seed predation was assessed from June to September in two of the treatments (bare fallow and oat–pea/rye–hairy vetch). Beetle activity-density varied with treatment, time of sampling, and year. In 2004 peak activity-density of A. aenea was highest in the mustard/buckwheat/canola, but there was no difference in H. pensylvanicus activity-density. In 2005 activity-density of H. pensylvanicus was higher in oat–pea/rye–hairy vetch than in soybean treatment. Seed predation rates were relatively consistent across treatments, averaging between 38 and 63%. In fallow and oat–pea/rye–hairy vetch, H. pensylvanicus activity-density accounted for 29 and 33% of the variation in seed predation, respectively. Our findings suggest cover crops have a positive effect on the activity-density of A. aenea and H. pensylvanicus and that disturbance negatively influences their activity-density in the absence of cover crops. Nomenclature: Buckwheat, Fagopyrum esculentum Moench.; canola, Brassica napus L.; field pea, Pisum sativum L.; hairy vetch, Vicia villosa Roth; mustard, Sinapis alba L.; oat, Avena sativa L.; red clover, Trifolium pretense L.; rye, Secale cereale L.; soybean, Glycine max Merr.; Amara aenea DeGeer; Harpalus pensylvanicus DeGeer.

Effects of Seeding Rate and Poultry Litter on Weed Suppression from a Rolled Cereal Rye Cover Crop

Abstract Growing enough cover crop biomass to adequately suppress weeds is one of the primary challenges in reduced-tillage systems that rely on mulch-based weed suppression. We investigated two approaches to increasing cereal rye biomass for improved weed suppression: (1) increasing soil fertility and (2) increasing cereal rye seeding rate. We conducted a factorial experiment with three poultry litter application rates (0, 80, and 160 kg N ha−1) and three rye seeding rates (90, 150, and 210 kg seed ha−1) in Pennsylvania and Maryland in 2008 and 2009. We quantified rye biomass immediately after mechanically terminating it with a roller and weed biomass at 10 wk after termination (WAT). Rye biomass increased with poultry litter applications (675, 768, and 787 g m−2 in the 0, 80, and 160 kg N ha−1 treatments, respectively), but this increased rye biomass did not decrease weed biomass. In contrast, increasing rye seeding rate did not increase rye biomass, but it did reduce weed biomass (328, 279, and 225 g m−2 in the 90, 150, and 210 kg seed ha−1 treatments, respectively). In 2009, we also sampled ground cover before rolling and weed biomass and density at 4 WAT. Despite no treatment effects, we found a correlation between bare soil before rolling (%) and weed biomass at 4 WAT. Our results suggest that increased rye seeding rate can effectively reduce weed biomass and that ground cover in early spring can influence weed biomass later in the growing season. Nomenclature: Cereal rye, Secale cereale L.

2,4-Dichlorophenoxyacetic acid (2,4-D)–resistant crops and the potential for evolution of 2,4-D–resistant weeds

In their recent article, we feel that Wright et al. (1) misrepresented the potential for 2,4-dichlorophenoxyacetic acid (2,4-D)–resistant weeds in 2,4-D–resistant cropping systems and exaggerated the sustainability of their approach to addressing glyphosate-resistant weed problems in agriculture.

Effects of Management Type and Timing on Weed Suppression in Soybean No-Till Planted into Rolled-Crimped Cereal Rye

Abstract Knowledge of weed emergence periodicity can inform the timing and choice of weed management tactics. We tested the effects of weed management system (conventional [CNV] and herbicide-free [HF]), timing of rye sowing (two dates), timing of soybean planting (5 planting dates, 3 in each system), and supplemental control (with and without) on weed suppression and weed community composition in soybean no-till planted into a cereal rye cover crop. Cereal rye was terminated with a roller-crimper and herbicide (CNV) or with a roller-crimper alone (HF), and supplemental weed control was achieved with a postemergence glyphosate application (CNV) or with interrow high-residue cultivation (HF). Supplemental control with glyphosate in CNV was more effective than high-residue cultivation in HF. When soybean was planted on the same date, CNV resulted in less weed biomass and a more even community composition, whereas HF resulted in greater weed biomass, dominated by common ragweed. When we controlled for cereal rye biomass and compared the effects of cereal rye sowing and termination timing within each system, earlier management reduced weed biomass in HF, but tended to increase weed biomass in CNV. Our results suggest the ability to control emerged weeds prior to soybean planting is an important factor that influences the optimal cereal rye cover crop management timing for weed suppression. Nomenclature: Common ragweed, Ambrosia artemisiifolia L.; cereal rye, Secale cereale L. ‘Aroostook’; soybean, Glycine max (L). Merr.