Kris J. Mahoney

Integrated Weed Management: Knowledge-Based Weed Management Systems

Abstract The fundamental role of integrated weed management (IWM) is to provide a source of scientifically based knowledge from which growers can make informed weed-management decisions. The objectives of this article include (1) highlighting the essential knowledge base required for the success of an IWM cropping system, (2) identifying the barriers to acceptance of IWM, and (3) discussing the future research opportunities for IWM. The minimum knowledge base consists of four key components: the effect of tillage on weed population dynamics, the time of weed emergence relative to the crop, the critical period for weed control, and the concept of a harvest window. There are substantial barriers, however, that reduce the willingness of growers to adopt the components of an IWM cropping system. IWM systems can be perceived as unreliable resulting in increased risk to management. No direct economic benefit can be defined clearly nor has there been sustained support for the adoption of IWM. In the future, IWM must change from a descriptive to a predictive science. As new markets evolve for agricultural products, new quality issues will arise that may influence weed management. Environmental auditing of IWM systems in terms of ISO 14000 accreditation, total carbon credits, or energy use will provide an important template from which comparisons of alternative weed-control strategies can be assessed. IWM strategies must be developed to reduce the risk to management and to gain broader support from the crop-protection industry, growers, and government.

Certified Crop Advisors’ Perceptions of Giant Ragweed (Ambrosia trifida) Distribution, Herbicide Resistance, and Management in the Corn Belt

Abstract Giant ragweed has been increasing as a major weed of row crops in the last 30 yr, but quantitative data regarding its pattern and mechanisms of spread in crop fields are lacking. To address this gap, we conducted a Web-based survey of certified crop advisors in the U.S. Corn Belt and Ontario, Canada. Participants were asked questions regarding giant ragweed and crop production practices for the county of their choice. Responses were mapped and correlation analyses were conducted among the responses to determine factors associated with giant ragweed populations. Respondents rated giant ragweed as the most or one of the most difficult weeds to manage in 45% of 421 U.S. counties responding, and 57% of responding counties reported giant ragweed populations with herbicide resistance to acetolactate synthase inhibitors, glyphosate, or both herbicides. Results suggest that giant ragweed is increasing in crop fields outward from the east-central U.S. Corn Belt in most directions. Crop production practices associated with giant ragweed populations included minimum tillage, continuous soybean, and multiple-application herbicide programs; ecological factors included giant ragweed presence in noncrop edge habitats, early and prolonged emergence, and presence of the seed-burying common earthworm in crop fields. Managing giant ragweed in noncrop areas could reduce giant ragweed migration from noncrop habitats into crop fields and slow its spread. Where giant ragweed is already established in crop fields, including a more diverse combination of crop species, tillage practices, and herbicide sites of action will be critical to reduce populations, disrupt emergence patterns, and select against herbicide-resistant giant ragweed genotypes. Incorporation of a cereal grain into the crop rotation may help suppress early giant ragweed emergence and provide chemical or mechanical control options for late-emerging giant ragweed. Nomenclature: Glyphosate; giant ragweed; Ambrosia trifida L. AMBTR; common earthworm; Lumbricus terrestris L.; corn; Zea mays L.; soybean, Glycine max (L.) Merr.

Nitrogen and Light Affect the Adaptive Traits of Common Lambsquarters (Chenopodium album)

Abstract Weeds are often portrayed as growing in resource-rich environments. However, weeds growing within crops often deal with variable nitrogen (N) availability and reduced levels of light quantity and quality as a result of the crop canopy. In order to explore how weeds adapt to such stressful growing conditions, growth-cabinet studies were conducted using common lambsquarters as a model weed to determine how light, defined in terms of photosynthetic photon flux density (PPFD) and quality (red to far-red light ratio [R/FR]), and N stress influence the expression of adaptive traits that contribute to survival. Development rate of common lambsquarters was not influenced by low N; however, low N in addition to low R/FR delayed the rate of leaf appearance. Main-stem leaf number was reduced by low PPFD but was insensitive to N and R/FR. Neither doses of N had any influence on the shoot-to-root ratio. Plants also responded to the interaction of light and N. Under low PPFD and high N, plants adapted by growing taller, increasing biomass allocation to leaves, and producing more leaf area per mol of accumulated incident PPFD. Plants adapted to the most stressful treatment combination of low PPFD and low N by producing thinner leaves and increasing inflorescences per mol of accumulated incident PPFD. Seed production was reduced under low PPFD, but 1,000-seed weight and carbon concentration was unaffected. Although reduced in number, the total N concentration of the seed increased under low PPFD treatments, especially under low N. The adaptive traits identified in this study provide a greater understanding of the survival and persistence of common lambsquarters. Nomenclature: Common lambsquarters, Chenopodium album L.

Biennial wormwood (Artemisia biennis) biomass allocation and seed production

Abstract Biennial wormwood has become an important weed problem in the northern Great Plains, but little is known about its biology. Biennial wormwood seeds were collected from Fargo, ND, and Fergus Falls, MN, for field experiments in 1999 and 2000 to determine the influence of transplanting date on growth, biomass, and seed production. Seeds were seeded in a greenhouse every 2 wk, and seedling rosettes were transplanted to the field 2 wk after emergence from April 30 until September 15 to simulate season-long emergence. Weekly destructive subsampling started 2 wk after transplanting and ended on September 29 in both years. All seedlings that grew for at least 5 wk after transplanting produced flowers by mid- to late August of the same year. Late-transplanted seedlings with less than 5 wk of growth did not flower or survive the winter. Biennial wormwood biomass allocation patterns resemble those of an annual species, with about 15% of the total dry weight allocated to roots, 20% to stems, 25% to leaves, and 40% to flowers. Transplant date had a substantial influence on biomass partitioning. Seedlings transplanted early in the growing season produced more biomass and seed than late-season transplants. Biennial wormwood seedlings transplanted on April 30 produced over 435,000 seeds per plant, whereas seedlings transplanted on August 15 produced 500 to 3,000 seeds. Biennial wormwood was photoperiod sensitive and flowered when the day length was about 14 h or less, between August 18 and 25, in both years. Nomenclature: Biennial wormwood, Artemisia biennis Willd. ARTBI.

Weed Management in Conventional- and No-Till Soybean Using Flumioxazin/Pyroxasulfone

Abstract Eleven field experiments were conducted over a 3-yr period (2010, 2011, and 2012) in conventional- and no-till soybean with a flumioxazin and pyroxasulfone premix. PRE and preplant applications were evaluated for soybean injury, weed control, and yield compared to standard herbicides. Early-season soybean injury from flumioxazin/pyroxasulfone ranged from 1 to 19%; however, by harvest, soybean yields were similar across labeled rates (160 and 200 g ai ha−1), standard treatments, and the nontreated control. Flumioxazin/pyroxasulfone provided excellent control (99 to 100%) of velvetleaf, pigweed species (redroot pigweed and smooth pigweed), and common lambsquarters across almost all rates tested (80 to 480 g ai ha−1). Common ragweed, green foxtail, and giant foxtail control increased with flumioxazin/pyroxasulfone rate. The biologically effective rates varied between tillage systems. The flumioxazin/pyroxasulfone rate required to provide 80% control (R80) of pigweed was 3 and 273 g ai ha−1 under conventional- and no-till, respectively. For common ragweed, the R80 was 158 g ai ha−1 under conventional tillage; yet, under no-till, the rate was nonestimable. The results indicate that flumioxazin/pyroxasulfone can provide effective weed control as a setup for subsequent herbicide applications. Nomenclature: Flumioxazin; pyroxasulfone; common lambsquarters; Chenopodium album L.; common ragweed; Ambrosia artemisiifolia L.; giant foxtail; Setaria faberi Herrm.; green foxtail; Setaria viridis (L.) Beauv.; redroot pigweed; Amaranthus retroflexus L.; smooth pigweed; Amaranthus hybridus L.; velvetleaf; Abutilon theophrasti Medik.; soybean; Glycine max (L.) Merr. Resumen Durante un período de 3 años (2010, 2011, y 2012), se realizaron once experimentos de campo usando pre-mezclas de flumioxazin y pyroxasulfone en soya con labranza convencional y cero labranza. Se evaluó el efecto de aplicaciones PRE y pre-siembra en el daño de la soya, el control de malezas, y el rendimiento en comparación con herbicidas estándar. El daño de la soya, temprano durante la temporada de crecimiento, producto de flumioxazin/pyroxasulfone varió entre 1 y 19%. Sin embargo, al momento de la cosecha, los rendimientos de la soya fueron similares al compararse las dosis de etiqueta (160 y 200 g ai ha−1), los tratamientos estándar, y el testigo sin tratamiento. Flumioxazin/pyroxasulfone brindó excelente control (99 a 100%) de Abutilon theophrasti, Amaranthus retroflexus, Amaranthus hybridus, y Chenopodium album en casi todas las dosis evaluadas (80 a 480 g ai ha−1). El control de Ambrosia artemisiifolia, Setaria viridis, y Setaria faberi aumentó con la dosis de flumioxazin/pyroxasulfone. Las dosis biológicamente efectivas fueron diferentes según el sistema de labranza. La dosis de flumioxazin/pyroxasulfone requerida para brindar 80% de control (R80) de Amaranthus spp. fue 3 y 273 g ai ha−1 en labranza convencional y en labranza cero, respectivamente. Para A. artemisiifolia, la R80 fue 158 g ai ha−1 en labranza convencional, aunque en labranza cero, la dosis no fue estimable. Los resultados indican que flumioxazin/pyroxasulfone puede brindar un control inicial de malezas efectivo que sirva de base para aplicaciones subsecuentes de otros herbicidas.

Control of Glyphosate-Resistant Giant Ragweed in Winter Wheat

Four field experiments were conducted over a 2-yr period (2012 and 2013) in winter wheat to evaluate POST herbicides for the control of glyphosate-resistant (GR) giant ragweed. POST herbicides were evaluated for winter wheat injury and GR giant ragweed control, population density, and aboveground biomass. The herbicides used in this study provided 54 to 90% and 51 to 97% control of GR giant ragweed at 4 and 8 wk after treatment (WAT), respectively. At 8 WAT, auxinic herbicide treatments or herbicide tank mix/premix treatments that contained auxinics provided 78 to 97% control of GR giant ragweed. Reductions in GR giant ragweed population density and aboveground biomass were 62 to 100% and 83 to 100%, respectively, and generally reflected the level of control. The results of this research indicate that Ontario, Canada, corn and soybean growers should continue to incorporate winter wheat into their crop rotation as one component of an integrated weed management (IWM) strategy for the control of GR giant ragweed. Nomenclature: Glyphosate; giant ragweed, Ambrosia trifida L.; winter wheat, Triticum aestivum L. Cuatro experimentos de campo fueron realizados durante un período de dos años (2012 y 2013) en trigo de invierno para evaluar herbicidas POST para el control de Ambrosia trifida resistente a glyphosate (GR). Se evaluó el efecto de los herbicidas POST sobre el daño en el trigo de invierno y el control, densidad de población y la biomasa aérea de A. trifida GR. Los herbicidas usados en este estudio brindaron 54 a 90% y 51 a 97% de control de A. trifida GR a 4 y 8 semanas después del tratamiento (WAT), respectivamente. A 8 WAT, los tratamientos con herbicidas tipo auxina o mezclas/pre-mezclas en tanque que contenían herbicidas tipo auxina brindaron 78 a 97% de control de A. trifida GR. Las reducciones en la densidad de la población y la biomasa aérea de A. trifida GR fueron 62 a 100% y 83 a 100%, respectivamente, y generalmente reflejaron el nivel de control. Los resultados de esta investigación indican que los productores de maíz y soja de Ontario, Canada, deberían continuar incorporando el trigo de invierno en sus rotaciones de cultivos como un componente de una estrategia de manejo integrado de malezas (IWM) para el control de A. trifida GR.

Control of Glyphosate-Resistant Horseweed in Winter Wheat with Pyrasulfotole Premixed with Bromoxynil

Five experiments were conducted over a 2-yr period (2013 and 2014) to evaluate POST herbicides in winter wheat fields with a history of glyphosate-resistant (GR) horseweed. Control 4 wk after treatment (WAT) with pyrasulfotole + bromoxynil was 95%. Control 8 WAT with 2,4-D, dicamba + MCPA + mecoprop, clopyralid, and pyrasulfotole + bromoxynil ranged from 89 to 97%; these herbicides also reduced GR horseweed density and biomass by 97 to 99%. Single mode of action herbicides like 2,4-D controlled GR horseweed; however, multiple modes of action should be used to prevent populations from becoming incrementally more resistant under repeated selection pressure. Nomenclature: Glyphosate; horseweed, Conyza canadensis (L.) Cronq.; winter wheat, Triticum aestivum L. Cinco experimentos fueron realizados durante un período de dos años (2013 y 2014) para evaluar herbicidas POST en campos de trigo de invierno con historial de Conyza canadensis resistente a glyphosate (GR). El control 4 semanas después del tratamiento (WAT) con pyrasulfotole + bromoxynil fue 95%. El control 8 WAT con 2,4-D, dicamba + MCPA + mecoprop, clopyralid, y pyrasulfotole + bromoxynil varió de 89 a 97%. Estos herbicidas también redujeron la densidad y la biomasa de C. canadensis GR en 97 a 99%. Herbicidas con un solo modo de acción, tales como 2,4-D, controlaron C. canadensis GR. Sin embargo, se deberían usar múltiples modos de acción para prevenir que las poblaciones se vuelvan incrementalmente más resistentes como consecuencia de una selección de presión repetida.

Examining the plant-back interval for glyphosate/glufosinate-resistant corn after the application of ACCase inhibitors.

Field experiments in 2013 and 2014 examined corn (Zea mays L.) tolerance to acetyl-coenzyme A carboxylase (ACCase) inhibiting herbicides in a scenario where they would have been used to terminate a failed corn stand prior to replanting. To simulate this, herbicides were applied 1 wk or 1 d preplant (PP) and several parameters were measured. Corn injury 1, 2, 4, or 8 wk after emergence (WAE) was similar to the untreated control, regardless of herbicide, rate, or PP application timing. Across herbicides and rates, PP timing did not affect plant stand and aboveground biomass 2 WAE, plant height 4 WAE, or yield. Across application timings, plant stand and aboveground biomass were similar to the untreated control, regardless of herbicide treatment or rate; however, some herbicides reduced height and (or) yield. For example, compared with the untreated control, fluazifop-p-butyl (75 and 150 g ha-1) and sethoxydim (300 g ha-1) each reduced height by about 3%, while clethodim (30 and 60 g ha-1), fluazifop-p-butyl (150 g ha-1), and quizalofop-p-ethyl (72 g ha-1) each reduced yield by about 2%. Therefore, in situations where a grower may need to terminate a failed corn stand, the selection of ACCase-inhibiting herbicides could be based on efficacy rather than plant-back restrictions.

Fulvic and humic acid fertilizers are ineffective in dry bean

Abstract: Studies were conducted in Ontario on dry bean (Phaseolus vulgaris L.) in 2010 and 2011 using fulvic acid (LX7®, MTS Environmental Inc.) or humic acid (Plant XL®, Alpha-Agri) fertilizers. Twenty fulvic acid field trials and 15 humic acid field trials indicate that these fertilizers were ineffective, as plant vigour, height, 100-seed weight, and yield were similar to a control treatment.

Post-emergence herbicides for control of glyphosate-resistant Canada fleabane in corn

Abstract: Post-emergence herbicides were evaluated for glyphosate-resistant Canada fleabane control in corn (Zea mays L.) from 2013 to 2015. By 8wk after treatment, dicamba/atrazine (96% control), dicamba (95% control), bromoxynil + atrazine (93% control), dicamba/diflufenzopyr (90% control), and tembotrione/thiencarbazone-methyl + dicamba (85% control) reduced population density and aboveground biomass to levels equivalent to the weed-free control.