Clarence J Swanton

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Verified

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• PhD
• University Professor Emeritus at University of Guelph

Oxidative stress responses of Arabidopsis to reflected low red to far-red signals (R:FR ≈ 0.3) generated by neighboring weeds or an artificial source of FR light were compared with a weed-free control (R:FR ≈1.6). In the low R:FR treatments, induction of the shade avoidance responses (SAR) coincided with increased leaf production of singlet oxygen...

Direct competition for resources is generally considered the primary mechanism for weed-induced yield loss. A re-evaluation of physiological evidence suggests weeds initially impact crop growth and development through resource-independent interference. We suggest weed perception by crops induce a shift in crop development, before resources become l...

Weed seeds present in the soil seedbank represent the most persistent threat to successful crop production. Despite our efforts with such selection pressures as herbicide technology, tillage, and mechanical and manual weed control, weeds continue to persist and challenge our weed management strategies. In this chapter, we explore five agronomic pra...

Nitrogen stress plays a critical role in corn yield reduction. Thermal remote sensing has many applications: as an assessment tool for urban heat island, as an ecological indicator of ecosystem development, and as a water-stress-detection tool. In this study, it was hypothesized that corn crops supplied with optimum or high rates of nitrogen would...

Multiple herbicide-resistant populations of horseweed [ Conyza canadensis (L.) Cronquist] continue to spread rapidly throughout Ontario, notably in areas where no-till soybean [Glycine max (L.) Merr.] are grown. The occurrence of multiple herbicide resistance within these populations suggests that the future role of herbicide tank mixtures as a mea...

Photosynthetic responses of common bean ( Phaseolus vulgaris L.) to increasing durations of weed-free and weedy environments were investigated using a critical period for weed control study under field conditions. The presence of weeds induced the shade avoidance response and was accompanied by a reduced red to far-red ratio (R/Fr) of reflected lig...

Recent studies indicate that thiamethoxam (TMX), a neonicotinoid insecticide, can affect plant responses to environmental stressors, such as neighboring weeds. The molecular mechanisms behind both stable and environmentally-specific responses to TMX likely involve genes related to defense/stress responses. We investigated the effect of a TMX seed t...

Nitrogen is one of the most important yield‐limiting nutrients for corn (Zea mays). The ability of thermal remote sensing to detect nitrogen deficiency in corn may enable precision agriculture to modify nitrogen rates according to field conditions. This study applies the exergy destruction principle as a theory to explain the inverse relationship b...

The number of fertilized florets around silking determines the number of kernels in maize (Zea mays L). In this study, we examined the relationship between plant dry matter accumulation, ear initial length and floret number. What does this relationship look like between the V7 to V9 growth stages and how does it change when the plants are subjected...

The development of a linuron-free weed management strategy for carrot production is essential as a result of the herbicide reevaluation programs launched by the Pest Management Regulatory Agency in Canada for herbicides registered before 1995 and the discovery of linuron-resistant pigweed species in Ontario. Field trials were conducted in one of On...

Sustainably feeding the next generation is often described as one of the most pressing “grand challenges” facing the 21st century. Generally, scholars propose addressing this problem by increasing agricultural production, investing in technology to boost yields, changing diets, or reducing food waste. In this paper, we explore whether global food p...

Available Kilocalories and their equivalent servings from the FAO’s Food balance sheets for agricultural year 2011. Serving calculations were based on Canada’s Food Guide serving sizes and USDA guidelines. (PDF)

The amount of food produced, their uses for human food and livestock feed and arable land area under each food group based on FAO 2011 data. (PDF)

Breakdown of greenhouse gas emissions by food category. (PDF)

The discipline of weed science is at a critical juncture. Decades of efficient chemical weed control have led to a rise in the number of herbicide-resistant weed populations, with few new herbicides with unique modes of action to counter this trend and often no economical alternatives to herbicides in large-acreage crops. At the same time, the worl...

In order to intensify agricultural productivity while at the same time enhance ecosystem services, it is necessary to evaluate carefully how current weed-management technologies are deployed, including herbicides and herbicide-resistant crops. Herbicide chemistries and herbicide-resistant crops have provided excellent technologies that have resulte...

Six field trials were conducted over a 2-yr period (2014 and 2015) at two locations in southwestern Ontario to compare the level of weed control provided by dicamba applied alone and in combination with dimethenamid-P applied before planting (preplant, PP) in glyphosate- and dicamba-resistant soybean to current industry standards when used in a two...

Intraspecific competition among crop plants is undesirable. Less competitive crops are predicted to increase yield and decrease the need for added resources. Wild plants demonstrate the ability to recognize kin and potentially help their relatives by reducing their competitive behaviours, a form of altruism. Altruism can also evolve through multile...

Soybean resistant to both glyphosate and dicamba (Roundup Ready 2 Xtend™) has been developed by Monsanto and is commercially available for the first time in 2016 in Canada. Six field trials were conducted over a two-year period (2014, 2015) at three locations in Southwestern Ontario to determine whether there is a benefit of including dicamba with...

Identity recognition systems allow plants to tailor competitive phenotypes in response to the genetic relatedness of neighbours. There is limited evidence for the existence of recognition systems in crop species and whether they operate at a level that would allow for identification of different degrees of relatedness. Here, we test the responses o...

Main conclusion: The interaction between neighboring weed-induced far-red enriched light and thiamethoxam can significantly alter soybean seedling morphology, nodulation, isoflavone levels, UV-absorbing phenolics, and carbon and nitrogen content. Neonicotinoid insecticides that are widely used on major crop plants can enhance plant growth and yiel...

Two studies consisting of six field experiments each were conducted at three locations in southwestern Ontario, Canada, in 2014 and 2015 to evaluate the possible antagonism when dicamba was added to quizalofop-p-ethyl or clethodim for the control of volunteer glyphosate-resistant (GR) corn. At 4 wk after application (WAA), quizalofop-p-ethyl at 24,...

Light signalling is an important mechanism of plant competition during the early stages of seedling development. Far-red-enriched (FR-E) light reflected from neighbouring weeds has been shown to induce the shade avoidance response leading to changes in plant morphology and increased variability in yields. In this study, the morphological and molecu...

In maize (Zea mays L.), as in other grass species, stem elongation occurs during growth and most noticeably upon the transition to flowering. Genes that reduce stem elongation have been important to reduce stem breakage, or lodging. Stem elongation has been mediated by dwarf and brachytic/brevis plant mutants that affect giberellic acid and auxin p...

Crop and weed competition studies rarely determine how plant-to-plant interactions alter the structure and physiology of crop roots. Soybean has the ability to detect neighboring weeds and to alter growth patterns including the allocation of resources to root growth. In this study, we hypothesized that low red:far red light ratio (R:FR) reflected f...

Light signals such as the red to far-red ratio (R/FR) reflected from stem and leaf surfaces of neighboring weeds can trigger a shade avoidance response in maize seedlings, resulting in morphological changes. Two different experiments were conducted under conditions of non-limiting resources with the objective to determine the effect of neighboring...

Background Thiamethoxam, is a broad-spectrum neonicotinoid insecticide which when applied to seed, has been observed to enhance seedling vigour under environmental stress conditions. Stress created by the presence of neighbouring weeds is known to trigger the accumulation of hydrogen peroxide (H2O2) in maize seedling tissue. No previous work has ex...

The annual global economic loss caused by weeds has been estimated at more than $100 billion U.S. dollars (Appleby et al. 2000). Additionally, worldwide annual herbicide sales are in the range of U.S. $25 billion (Agrow 2003). In light of these large dollar figures, it becomes clear that a greater understanding of crop—weed interactions is essentia...

Understanding abundance and distribution of weed species within the landscape of an agroecosystem is an important goal for weed science. Abundance is a measure of the number or frequency of individuals in an area. Distribution is a measure of the geographical range of a weed species. The study of weed population's abundance and distribution is help...

Red sorrel is a common, ramet-producing herbaceous creeping perennial species in wild blueberry fields. Flowering and seed production occur primarily in overwintering ramets in Nova Scotia, Canada, and growers may therefore be able to adopt fairly simple management strategies to reduce or prevent flowering and seed production in this species. The o...

Red sorrel (Rumex acetosella L.) is a ramet-producing herbaceous creeping perennial species commonly found as a weed in commercially managed lowbush blueberry (Vaccinium angustifolium Aiton) fields in Nova Scotia, Canada. Flowering and seed production occur primarily in overwintering ramets of this species, indicating a potential vernalization requ...

BACKGROUND: Far red light is known to penetrate soil and delay seed germination. Thiamethoxam as a seed treatment has been observed to enhance seed germination. No previous work has explored the effect of thiamethoxam on the physiological response of buried maize seed when germinating in the presence of above-ground weeds. We hypothesised that the...

Background Far red light is known to penetrate soil and delay seed germination. Thiamethoxam as a seed treatment has been observed to enhance seed germination. No previous work has explored the effect of thiamethoxam on the physiological response of buried maize seed when germinating in the presence of above ground weeds. We hypothesized that the c...

Stress caused by early weed competition is known to delay the rate of maize development which may result in a decrease in kernel number. Kernel number in maize is correlated negatively with the length of the anthesis-silking interval (ASI). A short ASI has been identified as an easily measured, visual trait which may identify enhanced drought toler...

Whole-plant bioassays using sugar beet, lettuce, cucumber, green bean, pea, and soybean as test crops were used to detect mesotrione residues in the soil. The test crops were planted in soil treated with mesotrione in the field the previous year at rates of 0 to 560 g ai ha(-1) and in nontreated soil from the same field, with mesotrione added at co...

Two field residue studies were conducted from 2005 to 2007 in Simcoe, Ontario, Canada, to evaluate the effects of mesotrione soil residues on injury, plant dry weight, and yield of sugar beet, cucumber, pea, green bean, and soybean and to verify the potential of reducing a 2-yr field-residue study (conventional residue carryover) to a 1-yr field st...

Early physiological mechanisms that occur in crop plants in response to neighboring weeds are not well understood. In this experiment, it was hypothesized that, in the absence of direct competition for resources, low red to far red ratio (R:FR) reflected from neighboring weeds will modulate the phenylpropanoid pathway, increase hydrogen peroxide (H...

Control of early-emerging weeds is essential to protect the yield potential of maize. An understanding of the physiological changes that occur as a result of weed interference is required to address variability in yield loss across sites and years. Field trials were conducted at the University of Guelph (UG), the Ohio State University (OSU), and Co...

The physiological process underlying grain yield (GY) loss in maize as a result of weed competition is not understood clearly. We designed an experiment to test the hypotheses that early season stress caused by the presence of neighboring weeds will increase plant-to-plant variability (PPV) of individual plant dry matter (PDM) within the population...

Sønderskov M, Swanton CJ & Kudsk P (2012). Influence of nitrogen rate on the efficacy of herbicides with different modes of action. Weed Research 52, 169–177. Outdoor pot experiments and field experiments were conducted to examine the influence of nitrogen rate on herbicide efficacy. Growth of unsprayed Tripleurospermum inodorum increased with incr...

The critical period for weed control (CPWC) is an integral component of integrated weed management strategies. Several studies have defined the CPWC in soybean under varying agronomic conditions, yet none have described the mechanisms involved in crop yield losses caused by weed competition. We hypothesized that under nonresource-limiting condition...

The objective of this research was to evaluate the efficacy of various pre-emergence (PRE) and post-emergence (POST) herbicides for the control of volunteer adzuki bean (Vigna angularis (Willd.) Ohwi & Ohashi) in soybean (Glycine max L.). Trials were conducted at two locations in 2005, 2006, 2007, and 2009. Experiments were arranged in a randomized...

Una nueva formulación de saflufenacil + dimethenamid-P se ha introducido al mercado para el control de malezas gramíneas y hojas anchas en preemergencia en el maíz. Se hicieron experimentos de campo con esta nueva combinación de herbicidas en 2008 y 2009 en cuatro localidades en el sur de Ontario. El objetivo de este estudio fue determinar la dosis...

Weed thresholds are an integral component of an integrated weed management system (IWM). In this paper we review the literature on weed thresholds and examine the theory and applicability of thresholds within the context of a systems approach to IWM. The development of empirical models describing single and multi-species thresholds are reviewed and...

Previous studies have suggested that the reduction in the root/shoot ratio that accompanies the shade avoidance response may reduce the tolerance of individuals to subsequent nutrient or moisture limitations. In this work, we examined the impact of the shade avoidance response on maize seedling growth and development and the response of these plant...

Crop seedlings detect the presence of neighboring competitors by means of the red to far-red ratio (R/FR) of light reflected from the leaf surfaces of adjacent seedlings. Although previous studies have suggested that shifts in the R/FR initiate crop– weed competition, no studies have documented the R/FR of light reflected from weeds or explored how...

An argument is presented by which the role of pharmaceuticals and pesticides can both be viewed in terms of contributing to human health. Comparisons are made in terms of discovery and development, regulatory policies and environmental and human impacts. Both technologies target particular biological functions, and in many cases they target similar...

Afifi M & Swanton C (2011). Maize seed and stem roots differ in response to neighbouring weeds. Weed Research51, 442–450. Light signals such as the red to far-red ratio (R/FR) reflected from stem and leaf surfaces of neighbouring weeds can trigger a shade avoidance response in maize seedlings, resulting in a reduction in root biomass. In this exper...

Soltani, N., Mashhadi, R. H., Mesgaran, M. B., Cowbrough, M., Tardif, F. J., Chandler, K., Swanton, C. J. and Sikkema, P. H. 2011. The effect of residual corn herbicides on soybean injury and yield seeded in the same season. Can. J. Plant Sci. 91: 571-576. In rare situations, poor stands of corn are removed and reseeded to soybean later in the spri...

Recent studies have suggested that soybeans express shade avoidance in response to low red : far-red (R : FR) light reflected from neighboring plants and that this response may determine the onset and outcome of crop–weed competition. We tested the hypothesis that the low R : FR ratio would trigger characteristic shade avoidance responses in soybea...

The influence of eight early successional plant species from the boreal forest on photosynthetically active radiation (PAR) were compared using a controlled plant competition study. Four woody (green alder, Alnus crispa (Ait.) Pursh; upland willow, Salix humilis Marsh.; white birch, Betula papyrifera Marsh.; wild red raspberry, Rubus idaeus L.) and...

The partitioning of dry matter and nutrients into component plant parts was determined for a weedy population of Jerusalem artichoke (Helianthus tuberosus L.). The annual allocation pattern, studied over two growing seasons, was characterized by a relatively large distribution of energy to structural increases in height, leaf number, and lateral sp...

Weather variables, leaf blight, and airborne spores of Botrytis squamosa were monitored in onion field plots at the Holland–Bradford Marsh, Ontario, in 1976. Incidence of spores showed marked daily periodicities with peaks normally between 0900 and 1200 hours Eastern Standard Time (EST). Daily spore counts were low (< 85 spores) during 7 to 28 July...

Saflufenacil is a PRE herbicide for the control of broadleaf weeds. Field and growth room studies were conducted to explore the tolerance of corn to POST treatments of saflufenacil and BAS 781. Additionally, the potential use of sodium as a safener for saflufenacil was evaluated. Crop injury caused by saflufenacil or BAS 781 was 8 and 38%, respecti...

Crop seedlings detect the presence of neighboring competitors by means of the red to far-red ratio (R/FR) of light reflected from the leaf surfaces of adjacent seedlings. Although previous studies have suggested that shifts in the R/FR initiate crop– weed competition, no studies have documented the R/FR of light reflected from weeds or explored how...

Volunteer winter cereals are found sporadically in maize (Zea mays L.) fields across southern Ontario. Seven field trials were conducted over a two-year period (2006 and 2007) at four locations to determine the efficacy of five acetolactate synthase (ALS)-inhibiting herbicides for the control of volunteer cereals applied at two post-emergence appli...

Volunteer winter wheat (Triticum aestivum L.) is a sporadic weed found in corn (Zea mays L.) fields across southern Ontario. Eight trials were conducted over a 2-yr period (2006 and 2007) at four locations to determine the competitiveness of volunteer winter wheat in corn. A soft red winter wheat cultivar (Pioneer 25R47) was seeded at each location...

Volunteer adzuki bean within a corn crop can decrease corn yield and increase the adzuki bean seed bank. The objective of this research was to evaluate the efficacy of various preemergence (PRE) and postemergence (POST) herbicides for the control of volunteer adzuki bean [Vigna angularis (Willd.) Ohwi & Ohashi] in corn. Trials were conducted at two...

1. Introduction to Invasion Ecology 2. The Distribution and Abundance of Populations 3. The Structure and Dynamics of Populations 4. Sexual Reproduction 5. Asexual Reproduction 6. From Seed to Seedling 7. Growing Up, Getting Old and Dying 8. Competition 9. Herbivory, Parasitism, and Mutualism 10. Basic Community Concepts and Diversity 11. Community...

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

This book contains 14 chapters describing how and why plant invasions occur and explains the ecological principles that are important in understanding the potential for a species to become invasive. The ecology of invasive plants is presented and the use of this knowledge to facilitate management is discussed.

Seeding date and the duration of weed emergence influenced the duration of the critical weed-free period in carrot. The critical weed-free period extended up to 930 growing degree days (GDD), when carrot was seeded in late April. In contrast, the critical weed-free period was short and lasted 414 to 444 GDD, when seeded in mid to late May and weed...

Glyphosate-resistant (GR) cropping systems are popular and used extensively by producers. However, the long-term impacts of heavy reliance of this technology on weed community structure are not known. Five fully phased field experiments (two no-tillage and three conventional tillage) were established at four locations in southwestern Ontario where...

Mesotrione has recently been registered for weed control in maize in Ontario, Canada; however, there is still little information on the doses required to provide 90% control for the complete spectrum of broadleaved weeds that the product controls. Our objective was to determine mesotrione doses that would provide at least 90% control of four econom...

In production agriculture, it is not uncommon for a crop to experience both intra- and interspecific competition during the normal course of development. Although the competition between crop plants (i.e., intraspecifc) is often considered independently of crop-weed competition (i.e., interspecific), the mechanisms through which yields are reduced...

Muhlenbergia frondosa is a perennial grass native to eastern North America, which naturally inhabits moist to wet forest margins and openings, freshwater littoral habitats, and grasslands. In Canada, its spread as a weed appears to have coincided with changes in cultivation practices during the past few decades. Infestations in such crops as maize...

Page ER, Tollenaar M, Lee EA, Lukens L & Swanton CJ (2010). Shade avoidance: an integral component of crop–weed competition. Weed Research50, 281–288. Crop–weed competition is comprised of both resource dependent and resource independent processes. While many studies have focused on the role that resource dependant competition plays in reducing cro...

The persistence and movement of transgenic DNA in agricultural and natural systems is largely unknown. This movement poses a threat of horizontal gene transfer and possible proliferation of genetically modified DNA into the general environment. To assess the persistence of transgenic DNA in a field of Roundup Ready® corn, we quantified the presence...

Glyphosate-resistant (GR) crops have been adopted rapidly since their commercial introduction, and with the increase in commercially available crops resistant to glyphosate, continuous use of the same herbicide mode of action is now possible in some crop rotations. A 6-yr study was initiated to investigate the effects of conventional herbicides com...