Arable Weeds Research Articles

Controlling arable weeds with natural substances as bio-based herbicides.

Today farmers manage arable weeds with chemical tools or mechanical tillage practices. While the heavy reliance on synthetic herbicides in conventional arable farming is under discussion, the environmentally driven trend towards reduced tillage as a climate-smart agricultural practice becomes more prominent. These trends demand for alternative control methods of weeds. This greenhouse study investigates the control of 21 arable weeds with four natural substances. The experimental setup compared an untreated control with four natural substances (acetic, citric and pelargonic acid and magnesium chloride), and glyphosate was used as the common active ingredient for stubble and presowing herbicide applications. The level of necrotisation (0-100%) was used to assess the efficacy of herbicide treatment. The efficacy differs substantially among the bio-based herbicides. For all natural substances, pelargonic acid has the highest mean efficacy for controlling the weeds tested in this experiment. For most weeds, however, the efficacy of natural substances is much lower compared to glyphosate. Nevertheless, the results indicate that natural substances as bio-based herbicides have the potential to offer an increased target specificity and rapid degradation in the soil. We found a high efficacy of pelargonic acid for controlling Brassica napus.

The Potential of Arable Weeds to Reverse Invertebrate Declines and Associated Ecosystem Services in Cereal Crops

There is global concern that invertebrate populations are declining rapidly, particularly in agricultural habitats. Declines have been attributed to the intensification of farming systems, with many studies focussing on a lack of semi-natural habitat in the landscape and the use of insecticides. However, within-field arable weeds are also an important driver of invertebrate abundance and the ecosystem services to which they contribute. This study focuses on the role of arable weeds in supporting invertebrate populations and selected ecosystem services they deliver., using winter wheat as a case study. Weed-invertebrate relationships were investigated across seven studies of winter-sown wheat spanning 18 years. Both phytophagous and predatory invertebrates responded to weed cover but to different degrees. Phytophages showed a stronger positive relationship with weed cover than the predators, because they rely on the resources provided by the weeds whereas predatory species response is likely to be mediated by their prey. Farmland bird chick-food indices were positively related to both broadleaf and grass cover in cropped fields, indicating that increased weed cover can provide increased invertebrate food for birds in winter wheat. Despite this potential, there were insufficient invertebrate food resources for birds in the majority of wheat fields sampled. Weed diversity did not play a significant role in moderating the relationships between weeds and invertebrate abundance, however this may be a function of the low weed diversity in modern winter wheat fields. In this study the weed species most frequently shown to predict the invertebrate community were: Poa annua, Stellaria media, Fumaria officinalis, Sinapis arvensis, Senecio vulgaris, Persicaria lapathifolia, Sonchus spp., Matricaria discoidea, Persicaria maculosa, Agrostis spp., Lamium purpureum, Lamium album, Veronica spp, Atriplex spp., Myosotis spp. and Anagallis arvensis. We conclude that even in an intensively grown cereal, arable weeds can play an important role in maintaining and restoring invertebrate populations, that 10% weed cover is needed to fulfil the potential and that a successful outcome will be driven by the presence of weed species that support invertebrates that provide ecosystem services.

First Report of Tobacco Vein Banding Mosaic Virus Naturally Infecting Black Nightshade (Solanum nigrum) in China

Black nightshade (Solanum nigrum L. var. humile [Bernh.]) is a common solanaceous plant that is an arable weed and also used in herbal medicine in China (Wang et al. 2017b; Zhao et al. 2018). The weed occurs commonly in a wide variety of habitats, including orchards, fields, villages, and roadsides in southwest provinces in China. In May 2019, about 3% of black nightshade plants growing in a tomato field at Kunming city in Yunnan province in China were found showing typical symptoms of viral disease (chlorosis, mosaic, leaf twisting, and plant stunting). To identify the suspected virus, one plant with severe symptoms was chosen for small RNA sequencing. Total RNA was extracted from leaves of symptomatic tissues by TruSeq Small RNA Sample Prep Kits (Illumina, San Diego, CA), and a small RNA library was constructed and then sequenced by high-throughput sequencing (HTS) on an Illumina HiSeq 2500 platform. The analysis generated approximately 11.37 million Illumina reads (15 to 40 nt in length), of which more than 0.082 million reads were mapped to the tobacco vein banding mosaic virus (TVBMV) genome (reference sequence accession no. NC_009994.1). No other viruses and viroids were detected. Further observation by transmission electron microscopy showed that the negatively stained crude sap of two symptomatic plants contained flexuous, filamentous virus particles about 600 to 900 nm in length, typical of a potyvirus. To further confirm the results, total RNA was extracted using TRIzol reagent (Thermo Fisher Scientific, Carlsbad, CA), first-strand cDNA was synthesized from 1 µg of total RNA using an oligo dT primer and a random primer mix, and then fragments of the TVBMV-CP gene were amplified with specific primers (F, 5′-AATGACGAACAGACAGTTGATGCTG-3′; R, 5′-CACGCCACTCACACCAAGTAGG-3′; designed from the CP gene of an HTS-generated clone) by 2×T5 Super PCR Mix (Tsingke BioTech, China). After cloning into a pGEM-T vector (Promega Biotech, U.S.A.), six clones of each fragment were randomly chosen for Sanger sequencing (Tsingke BioTech). The clone sequences were identical, and this partial TVBMV sequence was then submitted to GenBank (accession no. MN331841). This new sequence was most similar to Chinese isolate XDBB-01 (95.1% nucleotide identity to the CP mRNA, accession MG880266.1, and 98.2% amino acid identity to the corresponding coat protein AYG97953.1). Ten additional black nightshade plants with similar symptoms and another three asymptomatic plants were randomly selected and tested for the presence of TVBMV using the same primers. All 10 symptomatic plants tested positive for TVBMV, whereas the asymptomatic plants tested negative by reverse transcription PCR (RT-PCR) (data not shown). Transmissibility of TVBMV from black nightshade to tomato (cultivar KP13) by aphids (Myzus persicae), which were present widely in the tomato fields in the region, was tested according to the method reported by Yu et al. (2007). At 21 days postinoculation, 10 out of 20 inoculated plants showed leaf twisting symptoms. RT-PCR confirmed the presence of TVBMV in these plants but not in plants without symptoms. Results from three biological repeats were consistent, demonstrating that black nightshade can serve as an effective inoculum source for TVBMV. TVBMV has been reported to infect tobacco, potato, Datura stramonium, wild eggplant, tomato, and sesame in China (Wang et al. 2017a). To our knowledge, this is the first report of TVBMV infecting S. nigrum in natural field conditions. Our findings indicate that S. nigrum in the field could be a reservoir of TVBMV to infect tomato and cause viral disease in tomato fields.

Which Traits Make Weeds More Successful in Maize Crops? Insights from a Three-Decade Monitoring in France.

A major aim in invasion biology is identifying traits distinguishing alien invasive and alien non-invasive plants. Surprisingly, this approach has been, so far, poorly used to understand why some arable weeds are abundant and widespread while others are rare and narrowly distributed. In the present study, we focused on the characteristics of successful weeds occurring in maize fields, one of the most important crops worldwide. Two national weed surveys conducted in France were used to identify increasing and decreasing species based on 175 and 484 surveyed fields in the 1970s and the 2000s, respectively. Weed trait values related to regional frequency, local abundance, and specialization to maize were identified with phylogenetic generalized least-squares (PGLS). We found a positive relationship between regional frequency and local abundance, i.e., the most widespread weeds were also locally more abundant. We highlighted that weeds with the C4 photosynthetic pathway and summer emergence were more abundant, more frequent, and more specialized to maize crops. More generally, we highlighted two successful strategies: On the one hand, traits related to a general weediness syndrome with rapid resource acquisition (high SLA and Ellenberg-N) and high colonization capacity (seed longevity, fecundity, and wind dispersal); on the other hand, traits related to specific adaptation to spring cultivation (thermophilous species with summer emergence, late flowering, and C4 photosynthetic pathway). Deviations from the abundancy–frequency relationships also indicated that species of the Panicoideae sub-family, species with Triazine-resistant populations, and neophyte species were more abundant than expected by their regional frequency. To some extent, it is therefore possible to predict which species can be troublesome in maize crops and use this information in weed risk assessment tools to prevent new introductions or favor early detection and eradication. This study showed how tools developed in functional and macro-ecology can be used to improve our understanding of weed ecology and to develop more preventive management strategies.

Recent changes in the frequency of plant species and vegetation types in Scania, S Sweden, compared to changes during the twentieth century

Based on data from three surveys of the vascular flora of the province of Scania, southernmost Sweden, conducted 1938–1971, 1987–2006 and 2008–2015, we analyse the change in frequency of individual species and groups of species associated with particular vegetation types. A majority of all species have experienced a change in frequency since 1938, and this turnover has continued in recent decades. The species showing the most dramatic declines since 1987 represent a mixture of arable weeds, grassland species and ruderals, but excludes forest species. In contrast, a majority of the most increasing species are escapes from cultivation that thrive under shaded conditions. The vegetation types showing the largest decreases since 1987 are all open seminatural grasslands and wetlands, while the vegetation types performing best are wooded. All vegetation types increasing since 1987 also increased during the 1900s; however, species of wooded types performed relatively better in recent decades, as opposed to the minimal increase observed for species of vegetation strongly influenced by human activities. Among decreasing vegetation types, those that have received much attention from conservationists, e.g. sand-steppe and calcareous fens tend to perform relatively better now than during the 1900s, while those that have received less attention, e.g. poor fens, oligotrophic waters and heaths, now comprise the most rapidly declining vegetation types. A majority of the species that decreased 1938–1996 also decreased 1987–2015, but, in general, species shown to have increased during the 1900s have not continued to increase.

Weed vegetation of arable land in Slovakia: diversity and species composition

Arable fields are among the most widespread habitats in Slovakia, but recently, there have been no studies regarding species composition and structure of weed vegetation in these fields. Therefore, we studied the structure of arable weed vegetation and detected α- and β-diversity. The dataset of 507 phytosociological relevés in different crop types contains 407 plant taxa in 46 plant families. Native plants dominated over aliens, archaeophytes dominated over neophytes, and 14 plants belonged to invasive taxa. The most common species in the dataset were <em>Tripleurospermum perforatum</em>, <em>Cirsium arvense</em>, and <em>Viola arvensis</em>. Weeds were mostly therophytes, b- and a-euhemerobic, competitors, and ruderals, reproducing by seeds and pollinated by insects. The β-diversity of weed vegetation decreased with elevation and temperature and was higher in the Pannonicum than the Carpaticum region. The highest β-diversity was established in fodder+fallow fields, followed by that in cereals and root-crop fields, and the smallest diversity was found in stubble. Beta-diversity increased from spring to summer and slightly decreased again in fall. Detrended correspondence analysis indicated that the major compositional turnover of weed vegetation was related to light, temperature, moisture, and elevation. Weed vegetation constitutes an important habitat in the landscape that provides refuge to many threatened plants, and this vegetation has important functions in the agro-ecosystem food chain.

The influence of bioactive mobile telephony radiation at the level of a plant community – Possible mechanisms and indicators of the effects

Abstract Environmental exposure to radiofrequency electromagnetic fields (RF-EMFs) from mobile telephony has rapidly increased in the last two decades and this trend is expected to continue. The effects of this exposure at plant community level are unknown and difficult to assess in a scientifically appropriate manner. Such an assessment can be scientifically adequate if a studied plant community is completely new and control-impact radiation treatment is used. In this review we aimed to predict ecological effects and identify indicators of the impact of bioactive RF-EMFs at the mobile telephony frequency range on plant communities. We considered the scenario where a plant community was exposed to radiation generated by a base transmitting station antenna mounted on a nearby mast. This plant community can be represented by mesic meadow, ruderal or arable weed community, or other herbaceous, moderately productive vegetation type. We concentrated primarily on radiation effects that can be recorded for a year since the exposure started. To predict them we used physical theories of radiowave propagation in vegetation and the knowledge on plants physiological responses to RF-EMF. Our indicators can be used for the detection of the impact of RF-EMFs on vegetation in a control-impact experiment. The identified indicators can be classified into the following groups: (1) canopy parameters; (2) plant characteristics to be measured in the field or laboratory in a number of individuals that represent the populations of selected species; (3) community weighted means/medians (CWMs) of plant traits and strategies; (4) the abundance of other organisms that interact with plants and can influence their fitness or population size. The group of canopy parameters includes mean height, vertical vegetation structure and dry weight of above-ground standing phytomass. Plant characteristics requiring biometric sampling in the field are plant height, the number of fruits and seeds, as well as seed viability. The group of plant traits that are calculated as CWMs covers seed releasing height, seed dispersal mode, SLA, leaf orientation, month of germination and flowering, Ellenberg’s light indicator value, and the proportion of individuals in the classes of competitors and stress tolerators according to Grime's CSR strategy scheme. The group of “non-plant” indicators includes primarily the frequency of flower visits by beetles, wasps, hoverflies, and bees that have their nests over ground. To detect ecological responses that occur for the first year since a herbaceous community has been exposed to potentially bioactive RF-EMF, the first two indicators groups should be used.

Evaluation of the Risks of Contaminating Low Erucic Acid Rapeseed with High Erucic Rapeseed and Identification of Mitigation Strategies

High erucic acid rapeseed (HEAR) oil is under increasing demand for various industrial applications. However, many growers are concerned that if they grow the crop, they will not be able to revert to other rapeseed varieties in the future due to the risk of erucic acid (EA) contamination of the harvested seed and inability to maintain acceptable erucic acid thresholds. This review considered published literature and, using the same criteria as that used to contain transgenic crops, aimed to identify the key risks of erucic acid contamination, broadly prioritise them and identify pragmatic mitigation options. Oilseed rape has a number of traits that increase the risk of low erucic acid rapeseed (LEAR) crops being contaminated with EA from HEAR varieties. The quantity of seed produced and the potential for seed dormancy coupled with partial autogamy (self-fertilisation) facilitate the establishment and persistence of volunteer and feral populations. The large quantities of pollen produced when the crop is in flower mean there is also a high potential for cross-pollination. Self-sown volunteer plants represent the highest potential contamination risk, followed by the presence of arable weeds (e.g., wild mustard) whose seeds are also high in EA. Other risks arise from the cross-pollination of compatible wild relatives and the mixing of seed prior to sowing. It is important that both HEAR and LEAR varieties are appropriately managed since risks and their potential for mitigation arise throughout the entire LEAR crop production process. The length of rotation, type of tillage, cultivar choice, buffer zones, effective weed management and basic machinery hygiene are all factors that can reduce the risk of erucic acid contamination of LEAR crops and maintain the required thresholds.

Changing of crop species and agricultural practices from the Late Neolithic to the Bronze Age in the Zhengluo region, China

An assemblage of charred plant remains from 17 sites in the Zhengluo region has been collected and analyzed with a semi-quantitative method representative index and also with a multivariate statistical method correspondence analysis for this article. It provides a useful perspective for the understanding of the changing in the crop spectrum and crop husbandry practices from ca. 2500 BC to 1046 BC in this region. In the Longshan period, rice was subdominant while more dry-resistant broomcorn millet was cultivated during the Xinzhai and Erlitou periods; however, the importance of rice rose again in the Erlitou period, especially stood out in some central settlements and wheat witnessed a remarkable increase in the Shang period. Combined with the ecological information from arable weeds, it might conclude that agricultural techniques played a much more important role in farming since the Bronze Age. It is possible that in the Bronze Age, elaborate irrigation system, fertilizer practice, and spikelet-form storage method guaranteed the stable production and the preservation of crops, especially rice in some of the central settlements.

Middle-Neolithic agricultural practices in the Oldenburger Graben wetlands, northern Germany: First results of the analysis of arable weeds and stable isotopes

A number of small middle-Neolithic (3300–2800 BC) settlements flourished in the Oldenburger Graben area of northern Germany. The excavations yielded large amounts of crop remains, suggesting that agrarian production was a cornerstone of subsistence economy. Until about 3000 BC, Oldenburger Graben was a fjord, which over time was separated from the Baltic Sea and became a lagoon. The location of the settlement in the wetlands would have been highly favourable, offering a range of terrestrial and aquatic resources. Nonetheless, it may have been challenging to the Neolithic farmers, as perhaps not much dry land was available for crop growing. The success of agrarian production likely depended on the methods employed. This is an initial attempt at reconstructing strategies of agricultural land use during the middle-Neolithic occupation of the Oldenburger Graben lowland. We combine information on the habitat preferences and life history of arable weeds, and the recently obtained carbon and nitrogen stable isotope values on crop grains from one of the sites. The evidence allows us to glean practices that crop cultivation may have entailed, including potential strategies aimed at improving productivity of arable land such as tillage, weeding and manuring. Although preliminary, the observations point at potentially different management of emmer and barley, perhaps due to their variable importance to the Neolithic residents. This is the first time that stable isotope analysis on crops from northern Germany is used to elucidate agricultural practices of the Funnelbeaker communities of the middle-Neolithic.

The contribution of spatial mass effects to plant diversity in arable fields.

In arable fields, plant species richness consistently increases at field edges. This potentially makes the field edge an important habitat for the conservation of the ruderal arable flora (or ‘weeds’) and the invertebrates and birds it supports. Increased diversity and abundance of weeds in crop edges could be owing to either a reduction in agricultural inputs towards the field edge and/or spatial mass effects associated with dispersal from the surrounding landscape.We contend that the diversity of weed species in an arable field is a combination of resident species, that can persist under the intense selection pressure of regular cultivation and agrochemical inputs (typically more ruderal species), and transient species that rely on regular dispersal from neighbouring habitats (characterised by a more ‘competitive’ ecological strategy).We analysed a large dataset of conventionally managed arable fields in the UK to study the effect of the immediate landscape on in‐field plant diversity and abundance and to quantify the contribution of spatial mass effects to plant diversity in arable fields in the context of the ecological strategy of the resulting community.We demonstrated that the decline in diversity with distance into an arable field is highly dependent on the immediate landscape, indicating the important role of spatial mass effects in explaining the increased species richness at field edges in conventionally managed fields.We observed an increase in the proportion of typical arable weeds away from the field edge towards the centre. This increase was dependent on the immediate landscape and was associated with a higher proportion of more competitive species, with a lower fidelity to arable habitats, at the field edge. Synthesis and applications. Conserving the ruderal arable plant community, and the invertebrates and birds that use it as a resource, in conventionally managed arable fields typically relies on the targeted reduction of fertilisers and herbicides in so‐called ‘conservation headlands’. The success of these options will depend on the neighbouring habitat and boundary. They should be placed along margins where the potential for ingress of competitive species, that may become dominant in the absence of herbicides, is limited. This will enhance ecosystem services delivered by the ruderal flora and reduce the risk of competitive species occurring in the crop.

A survey of whitefly-transmitted viruses on tomato crops in South Africa

Whitefly-transmitted viruses are a growing threat to modern day agriculture. Their impact on South Africa's vegetable industry results in unprecedented economic losses. Tomatoes are important vegetable crops that are highly susceptible to whiteflies and an almost indispensable part of meal preparation in many South African homes. Against this background, tomato crops and nearby weed species in South Africa were surveyed for whitefly-transmitted viruses. In addition, some pepper crops in adjacent tomato fields were also included in this study. Field and greenhouse crops were inspected for the development of virus-like symptoms in the presence of whitefly infestations. Leaf samples exhibiting virus-like symptoms were collected and analyzed for whitefly-transmitted crini-, torrado-, begomo-, ipomo- and carla viruses using molecular assays. The identity of each virus positive sample was confirmed by Sanger sequencing and used in subsequent phylogenetic studies. Tomato chlorosis crinivirus (ToCV), Tomato torrado virus (ToTV) and Tomato curly stunt begomovirus (ToCSV) were three major viruses identified in the study. ToCV was the most abundant whitefly-transmitted virus in South Africa with an overall prevalence of 47.1% (tomatoes) and 21% (weeds). ToCV isolates from South Africa matched ≥97% to isolates from Spain and Sudan. ToTV outbreaks emerged on tomato crops in the northern parts of South Africa in the presence of abnormally high whitefly populations. ToTV infections of tomatoes were restricted to the Limpopo province, however, a second isolate was identified on an unknown arable weed that did not infect nearby tomato crops. ToTV isolates from South Africa matched 99% and 92.8% to Polish and Italian isolates and had an overall incidence of 7.5% (tomatoes) and 11% (weeds). ToCSV isolates from South Africa matched 100% with Mozambican isolates. Phylogenetic analysis showed that current ToCSV isolates in South Africa were distantly related to a previously identified South African ToCSV isolate. The disease was identified on tomatoes in three provinces and had an overall incidence of 9.4%. On the contrary, whitefly-transmitted viruses were not identified on pepper crops exhibiting virus-like symptoms. In this study, whitefly-transmitted viruses infecting tomatoes, and some weed species in South Africa were elucidated. These findings are intended to raise awareness on the impact of whitefly-transmitted viruses in South Africa's tomato industry.

A functional diversity approach of crop sequences reveals that weed diversity and abundance show different responses to environmental variability

Abstract Combining several crop species and associated agricultural practices in a crop sequence has the potential to control weed abundance while promoting weed diversity in arable fields. However, how the variability in environmental conditions that arise from crop sequences affects weed diversity and abundance remains poorly understood, with most studies to‐date simply opposing weed communities in monoculture and in crop rotation. Here, we describe crop sequences along gradients of disturbance and resource variability using a crop functional trait and associated agricultural practices. We tested the hypothesis that in disturbances reduces weed abundance, whereas variability in resources promotes weed diversity. We used functional Hill's numbers to compute crop sequence functional diversity based on sowing date, herbicide spectrum and crop height—these are the respective proxies of disturbance timings, disturbance types and light availability. Using a large‐scale weed monitoring database, we assessed crop sequence diversity for 1,045 crop sequences of five consecutive cropping seasons. We computed weed richness and abundance at pluri‐annual (pool of weeds observed across five cropping seasons) and annual (pool of weeds observed during a winter cereal cropping season preceded by five cropping seasons) scales. We also accounted for herbicide and tillage intensities to test whether management intensity affects the response of weed diversity and abundance to crop sequence diversity. At the pluri‐annual scale, weed richness increased with the diversity of crop height and sowing date, whereas weed abundance decreased with sowing date diversity. Annual weed richness decreased with sowing date diversity, whereas annual weed abundance poorly relied on crop sequence diversity. Synthesis and applications. This study establishes a scientific basis for designing crop sequences according to specific weed management goals. We show that farmers may enhance arable weed diversity on a pluri‐annual scale by sequentially sowing crop species that differ in their competitive ability and sowing date. They may also achieve a better control of weed abundance by increasing the diversity of crop sowing dates across the crop sequence.

Lipid content drives weed seed consumption by ground beetles (Coleopterea, Carabidae) within the smallest seeds

SummarySeed predation by natural predators can contribute to the regulation of the weed seedbank, hence has been acknowledged as a promising way to significantly reduce the use of chemicals and mechanical weeding to manage arable weeds. However, the complex aspects that determine seed species preference are not yet fully understood, especially, the relationship between weed seed traits and the feeding behaviour of seed predator species. In this study, we examine predation on 42 weed species by four ground beetle species as a function of two major seed traits: seed mass and seed lipid content. We used an _original experimental design to create a statistically independent trait value distribution for evaluating the separate and interactive effects of these two traits. Our results show that all the ground beetles species consumed weed seeds, but at different rates. The smallest weed seeds with high lipid content were among the most consumed. While seed mass might be limiting for ground beetles, due to ease of handling or the thickness of the seed coat, they may preferentially consume seeds rich in lipids to increase energy uptake. To our knowledge, this study is the first to reveal that two major seed traits drive seed predation by ground beetles.

What makes a weed a weed? A large-scale evaluation of arable weeds through a functional lens.

Despite long-term research efforts, a comprehensive perspective on the ecological and functional properties determining plant weediness is still lacking. We investigated here key functional attributes of arable weeds compared to non-weed plants, at large spatial scale. We used an intensive survey of plant communities in cultivated and non-cultivated habitats to define a pool of plants occurring in arable fields (weeds) and one of plants occurring only in open non-arable habitats (non-weeds) in France. We compared the two pools based on nine functional traits and three functional spaces (LHS, reproductive and resource requirement hypervolumes). Within the weed pool, we quantified the trait variation of weeds along a continuum of specialization to arable fields. Weeds were mostly therophytes and had higher specific leaf area, earlier and longer flowering, and higher affinity for nutrient-rich, sunny and dry environments compared to non-weeds, although functional spaces of weeds and non-weeds largely overlapped. When fidelity to arable fields increased, the spectrum of weed ecological strategies decreased as did the overlap with non-weeds, especially for the resource requirement hypervolume. Arable weeds constitute a delimited pool defined by a trait syndrome providing tolerance to the ecological filters of arable fields (notably, regular soil disturbances and fertilization). The identification of such a syndrome is of great interest to predict the weedy potential of newly established alien plants. An important reservoir of plants may also become weeds after changes in agricultural practices, considering the large overlap between weeds and non-weeds.

Banded herbicide application in a conventional sunflower production system

Banded herbicide applications with hooded field sprayers (HFS) provide safer applications in many crops. The aim of this paper is to show the effectiveness and safeness of selective and nonselective herbicide applications in a conventional sunflower production system (CSPS) using a combined hooded field sprayer (CHFS). Glyphosate interrow and aclonifen or quizalofop-P-ethyl intrarow were applied in fields cropped with nonglyphosate-resistant sunflower varieties in Ankara, Tekirdağ, and Tokat Provinces of Turkey in 2015 and 2016. In Ankara and Tekirdağ, glyphosate caused limited injury to sunflower at 28 days after treatment (DAT), and aclonifen created transient phytotoxicity in 2015. Glyphosate was applied with aclonifen at 1.44 + 0.75 and 2.88 + 0.75 kg ai ha-1 or quizalofop-P-ethyl 1.44 + 0.05 and 2.88 + 0.05 kg ai ha-1 using band application units of CHFS together. Aclonifen and quizalofop-P-ethyl were also used at 0.75 and 0.05 kg ai ha-1, respectively, using the conventional application unit of CHFS. Glyphosate + aclonifen (1.44 + 0.75 and 2.88 + 0.75 kg ai ha-1) provided higher weed control and sunflower seed yield compared with the other treatments. Aclonifen (0.75 kg ai ha-1) controlled many competitive arable weeds and increased sunflower seed yield, except in Tokat in 2016, where common cocklebur was present in the field, which is not in the range of aclonifen. Weed control by glyphosate + quizalofop-P-ethyl (1.44 + 0.05 and 2.88 + 0.05 kg ai ha-1) was limited because broadleaf weeds covered the sunflower fields where the trials were conducted. Quizalofop-P-ethyl (0.05 kg ai ha-1) alone and untreated control were associated with the lowest sunflower seed yield. It is concluded that banded application of glyphosate is safe and effective in sunflowers. Applying glyphosate with aclonifen and quizalofop-P-ethyl with CHFS helps to save time and money, and mitigate CO2 emission.

The First Cases of Evolving Glyphosate Resistance in UK Poverty Brome (Bromus sterilis) Populations

AbstractPoverty brome (Bromus sterilisL.) [sterile or barren brome, syn.Anisantha sterilis(L.) Nevski] is a problematic UK arable weed. There are currently no confirmed cases of glyphosate resistance in any weed species in the United Kingdom or inB. sterilisworldwide. However, there are reports of poor control by glyphosate in this species. Here, we report experiments to confirm the suspected on-farm resistance ofB. sterilispopulations to glyphosate. Glyphosate screening and dose–response experiments established that glyphosate sensitivity of three UKB. sterilispopulations exhibiting poor field control is outside the normal range of sensitivity of 30 sensitive populations and adjacent unexposed populations. Control of sensitive populations ranged from 49% to 82% and for suspected resistant populations from 21% to 30%. Dose–response ED50values of sensitive populations ranged between 241 and 313 g ai ha−1; corresponding values of suspected resistant populations ranged between 420 and 810 g ha−1, and resistance indices ranged from 1.55 to 4.5. Suspected resistant populations were incompletely controlled at the recommended field rate of glyphosate (540 g ha−1), while adjacent unexposed populations were completely controlled. We conclude that some UK populations ofB. sterilishave reduced glyphosate sensitivity and are in the process of evolving resistance. This is the first reported case of reduced glyphosate sensitivity in any UK weed species and inB. sterilisworldwide. This, coupled with increasing glyphosate use, highlights the need for increased vigilance and monitoring for glyphosate resistance in the United Kingdom.

Crop competition in winter wheat has a higher potential than farming practices to regulate weeds

AbstractManagement of biotic interactions has been recognized as a potential substitute for costly agrochemical inputs. Competition is one of the most important biotic interactions known to regulate populations and govern species assemblages. However, although theoretical and empirical work has been produced on competition, in situ experimental evidence is much scantier, mainly because of the difficulty of manipulating competition in the field. Arable weeds offer an outstanding opportunity to meet this challenge, because of the relative ease of in situ experimental manipulation and because of the urgent need to find sustainable weed management strategies. Here, we assess the importance of crop competition and two main conventional farming practices (N fertilizer and weed control) on weed species richness, abundance, and biomass. We set up an experiment with a design with two factors, presence/absence of crops and presence/absence of N fertilizer and weed control, in working farm fields with winter cereals as the target crop. We found that the crop competition reduced weed biomass production by almost 65%, as a result of the crop's competitive advantage from its greater ability to take up N, while the effect on weed species richness was less important. Our results also show that the effect of crop competition on the weed assemblage was much stronger than the effect of N fertilizer and weed control. The decrease in weed abundance and biomass mainly resulted from a strong effect of the crop on the dominant species, while the abundance of intermediate species tended to be much less affected, a result consistent with studies in grasslands where the removal of the dominant species provides a competitive release for subordinate ones. Our results further give experimental support for crop competition as a way to reduce costly agricultural inputs for weed control. Conducting experiments with farmers in their field is a valuable approach to generate knowledge for the future delivery of sustainable management.

Biodiversity-based options for arable weed management. A review

In the context of a shift towards pesticide reduction in arable farming, weed management remains a challenging issue. Integrated Weed Management currently recommends agronomic practices for weed control, but it does not integrate the use of biodiversity-based options, enhancing the biological regulation of weeds. Here, wereview existing knowledge related to three potentially beneficial interactions, of crop–weed competition, weed seed granivory, and weed interactions with pathogenic fungi. Our main finding are the following : (1) promoting cropped plant–weed competition by manipulating cropped cover could greatly contribute to weed reduction ; (2) weed seed granivory by invertebrates can significantly lower weed emergence, although this effect can be highly variable because seed predation is embedded within complex multitrophic interactions that are to date not fully understood ; (3) a wide range of fungi are pathogenic to various stages of weed development, but strain efficacy in field trials does not often match that in controlled conditions. We present a framework that superimposes biodiversity-based options for weed biocontrol on a classical Integrated Weed Management system. We then describe the current state of knowledge on interactions between agronomic practices and the organisms at play and between the different biological components of the system. We argue that further advances in our understanding of biodiversity-based options and their performance for weed biocontrol will require farm-scale experimental trials.

How effective is large landscape-scale planning for reducing local weed infestations? A landscape-scale modelling approach

Finding efficient and environmentally sustainable methods for arable weed management is a current challenge in agroecosystems. Weed species disperse over scales larger than the field. Landscape-scale management could, therefore, reinforce field-scale strategies for innovative cropping systems. In particular, the introduction of semi-natural habitats, such as permanent meadows, which are unsuitable habitats for annual arable weeds, could potentially reduce weed densities in crops. We developed a spatially explicit, landscape-scale model of annual arable weed population dynamics including the main components of weed management at cropping system level: crop rotation, tillage regime, intensity of herbicide use and mechanical weeding. The variability of responses to these factors for different weed species functional types was considered by modelling four functional response groups. We used this model to investigate the effects of increasing the proportion of permanent meadows in the landscape and of the spatial arrangement of meadows on weed density in crops. With this model, increasing the proportion of permanent meadows significantly decreased mean seed density of weeds in crops. Furthermore, weed density in crops was found to be lower for landscapes in which the meadows were scattered, rather than clustered together in large zones. However, these spatial and landscape-scale effects were much weaker than the local effect of cropping systems. Weed density in permanent meadows was more sensitive to the proportion of meadows and to their spatial arrangement than weed density in crops, although the absolute value of weed density remained low in this unfavourable habitat.