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A key challenge in the management of populations is to quantify the impact of interventions in the face of environmental and phenotypic variability. However, accurate estimation of the effects of management and environment, in large‐scale ecological research is often limited by the expense of data collection, the inherent trade‐off between quality and quantity, and missing data.In this paper we develop a novel modelling framework, and demographically informed imputation scheme, to comprehensively account for the uncertainty generated by missing population, management, and herbicide resistance data. Using this framework and a large dataset (178 sites over 3 years) on the densities of a destructive arable weed (Alopecurus myosuroides) we investigate the effects of environment, management, and evolved herbicide resistance, on weed population dynamics.In this study we quantify the marginal effects of a suite of common management practices, including cropping, cultivation, and herbicide pressure, and evolved herbicide resistance, on weed population dynamics.Using this framework, we provide the first empirically backed demonstration that herbicide resistance is a key driver of population dynamics in arable weeds at regional scales. Whilst cultivation type had minimal impact on weed density, crop rotation, and earlier cultivation and drill dates consistently reduced infestation severity.Synthesis and applications: As we demonstrate that high herbicide resistance levels can produce extremely severe weed infestations, monitoring herbicide resistance is a priority for farmers across Western Europe. Furthermore, developing non‐chemical control methods is essential to control current weed populations, and prevent further resistance evolution. We recommend that planning interventions that centre on crop rotation and incorporate spring sewing and cultivation to provide the best reductions in weed densities. More generally, by directly accounting for missing data our framework permits the analysis of management practices with data that would otherwise be severely compromised. [ABSTRACT FROM AUTHOR]

In 35 years of routine screening for herbicide resistance, a total of 3758 seed sample/herbicide combinations were assayed. Resistance testing was done in either pots in glasshouses (chlortoluron, fenoxaprop and mesosulfuron‐methyl + iodosulfuron‐methyl sodium) or Petri‐dishes in incubators (sethoxydim, cycloxydim and pendimethalin). With all herbicides, the relationship between herbicide efficacy and year of sampling was linear, with the slope representing the annual loss of efficacy. This was higher for the ALS inhibitors mesosulfuron + iodosulfuron (3.73% year−1) and ACCase inhibitors sethoxydim/cycloxydim (1.92% year−1) and fenoxaprop (1.36% year−1) than for the substituted urea chlorotoluron (0.69% year−1) and the dinitroaniline pendimethalin (1.10% year−1). These results are consistent with other studies on the relative resistance risk associated with these different modes of action. There was also a surprisingly good correlation between results for random and non‐random resistance testing, which has also been found in studies with other weed species in Canada and Australia. This indicates that routine testing of submitted samples can replace, at least partly, the need for random surveys which tend to be both labour intensive and expensive. These results, compiled over 35 years, show the value of routine resistance screening, not only for detecting resistance at the individual field level ('micro' scale), but also the distribution, evolution and impact of resistance country‐wide ('macro' scale). However, it is important that standardised testing methods, including appropriate reference populations, are used by different testing centres to ensure consistent results. [ABSTRACT FROM AUTHOR]

Summary: Rapid adaptation of weeds to herbicide applications in agriculture through resistance development is a widespread phenomenon. In particular, the grass Alopecurus myosuroides is an extremely problematic weed in cereal crops with the potential to manifest resistance in only a few generations. Target‐site resistances (TSRs), with their strong phenotypic response, play an important role in this rapid adaptive response. Recently, using PacBio's long‐read amplicon sequencing technology in hundreds of individuals, we were able to decipher the genomic context in which TSR mutations occur. However, sequencing individual amplicons are costly and time‐consuming, thus impractical to implement for other resistance loci or applications. Alternatively, pool‐based approaches overcome these limitations and provide reliable allele frequencies, although at the expense of not preserving haplotype information. In this proof‐of‐concept study, we sequenced with PacBio High Fidelity (HiFi) reads long‐range amplicons (13.2 kb), encompassing the entire ACCase gene in pools of over 100 individuals, and resolved them into haplotypes using the clustering algorithm PacBio amplicon analysis (pbaa), a new application for pools in plants and other organisms. From these amplicon pools, we were able to recover most haplotypes from previously sequenced individuals of the same population. In addition, we analysed new pools from a Germany‐wide collection of A. myosuroides populations and found that TSR mutations originating from soft sweeps of independent origin were common. Forward‐in‐time simulations indicate that TSR haplotypes will persist for decades even at relatively low frequencies and without selection, highlighting the importance of accurate measurement of TSR haplotype prevalence for weed management. [ABSTRACT FROM AUTHOR]

Climate change is driving the need to investigate responses to water limitation of morphological traits involved in competition for light, the main resource for which crops and weeds compete in conventional temperature and tropical cropping systems, to better understand field crop–weed dynamics. Our objective was to develop an innovative approach to quantify weed species responses to water limitation, using three species. This approach combined (1) key morphological traits involved in competition for light (taken from a mechanistic crop–weed model) as criteria to analyse responses to water limitation and (2) a pot/greenhouse platform allowing automated precision‐watering and daily quantification of soil water availability in each pot. For all species and growth stages, increased plant height per unit of aboveground biomass and production of smaller/thicker leaves were the most noteable responses. Plants with a strong increase in plant height per unit of aboveground biomass in response to water limitation maintained high levels of specific leaf area, even at low soil water availability. Increases in biomass allocation to roots (vs. aboveground parts) and leaves (vs. stems and reproductive organs) were also observed, but not for all species and growth stages. Overall, these effects of water limitation on morphological traits indicate strong interactions between competition for light and water. [ABSTRACT FROM AUTHOR]

Globally, herbicide resistance in weeds poses a threat to food security. Resistance evolves rapidly through the co‐option of a suite of physiological mechanisms that evolved to allow plants to survive environmental stress. Consequently, we hypothesize that stress tolerance and herbicide resistance are functionally linked. We address two questions: (i) does exposure to stress in a parental generation promote the evolution of resistance in the offspring? (ii) Is such evolution mediated through non‐genetic mechanisms? We exposed individuals of a grass weed to drought, and tested whether this resulted in herbicide resistance in the first generation. In terms of both survival and dry mass, we find enhanced resistance to herbicide in the offspring of parents that had been exposed to drought. Our results suggest that exposure of weeds to drought can confer herbicide resistance in subsequent generations, and that the mechanism conferring heritability of herbicide resistance is non‐genetic. [ABSTRACT FROM AUTHOR]

Summary: The development of acetolactate synthase (ALS) tolerant sugar beet provides new opportunities for weed control in sugar beet cultivation. The system consists of an ALS−inhibiting herbicide (foramsulfuron + thiencarbazone‐methyl) and a herbicide‐tolerant sugar beet variety. Previously, the use of ALS‐inhibitors in sugar beet was limited due to the susceptibility of the crop to active ingredients from this mode of action. The postulated benefits of cultivation of the ALS‐tolerant sugar beet are associated with potential risks. Up to now, with no relevant proportion of herbicide‐tolerant crops in Germany, ALS‐inhibitors are used in many different crops. An additional use in sugar beet cultivation could increase the selection pressure for ALS‐resistant weeds. To evaluate the impact of varying intensity of ALS‐inhibitor use on two weed species (Alopecurus myosuroides and Tripleurospermum perforatum) in a crop rotation, field trials were conducted in Germany in two locations from 2014 to 2017. Weed densities, genetic resistance background and crop yields were annually assessed. The results indicate that it is possible to control ALS‐resistant weeds with an adapted herbicide strategy in a crop rotation including herbicide‐tolerant sugar beet. According to the weed density and species, the herbicide strategy must be extended to graminicide treatment in sugar beet, and a residual herbicide must be used in winter wheat. The spread of resistant biotypes in our experiments could not be attributed to the integration of herbicide‐tolerant cultivars, although the application of ALS‐inhibitors promoted the development of resistant weed populations. Annual use of ALS‐inhibitors resulted in significant high weed densities and caused seriously yield losses. Genetic analysis of surviving weed plants confirmed the selection of ALS‐resistant biotypes. [ABSTRACT FROM AUTHOR]

BACKGROUND: Shortawn foxtail (Alopecurus aequalis Sobol.) is a competitive grass weed infesting winter wheat‐ and canola‐growing fields in China. In May 2016, a suspected A. aequalis resistant population AHTC‐06 that survived fenoxaprop‐P‐ethyl and mesosulfuron‐methyl applied at their field‐recommended rates was collected from a wheat field in Jinji County, Anhui Province, China. This study aimed to determine the resistance profile of this AHTC‐06 population to ACCase‐ and ALS‐inhibitors, and to investigate its mechanisms of resistance to fenoxaprop‐P‐ethyl and mesosulfuron‐methyl. RESULTS: Two mutations, a common Ile‐2041‐Asn (ACCase gene) and a very rare Pro‐197‐Tyr (ALS1 gene), were both identified in resistant individual plants. The homozygous subpopulation AHTC‐06F1 for the two mutations was generated, and it showed broad‐spectrum resistance to APPs, DENs, and ALS‐inhibiting herbicides of all five chemical families tested, with resistance index (RI) values that ranged from 2.2 to 36.5. In vitro ALS activity assays showed the ALS from the resistant population was insensitive to all the tested ALS inhibitors, with RI values ranging from 3.10 to 22.51. Pre‐treatment with piperonyl butoxide (PBO) and malathion significantly (P < 0.05) reversed the weed's resistance to fenoxaprop‐P‐ethyl and mesosulfuron‐methyl, respectively. Two P450 genes, c21190_g1 and c43350_g3, were constitutively overexpressed and mesosulfuron‐methyl‐induced upregulated in resistant plants, for which c43350_g3 was also fenoxaprop‐P‐ethyl‐induced upregulated. CONCLUSION: This study confirms the first case of a grass weed featuring broad‐spectrum resistance to ALS‐inhibiting herbicides due to a Pro‐197‐Tyr mutation in the ALS gene. Fenoxaprop‐P‐ethyl and mesosulfuron‐methyl resistances in AHTC‐06 plants were conferred by target site mutations and P450s‐based metabolism. © 2018 Society of Chemical Industry The Pro‐197‐Tyr mutation was identified in the ALS gene of a grass weed, Alopecurus aequalis, with multiple resistance of its plants conferred by target site mutations and P450s‐based metabolism. [ABSTRACT FROM AUTHOR]

Summary: Cover crops can suppress weeds within agricultural fields due to competitive and allelopathic effects. Glasshouse experiments were conducted to evaluate the relative proportions of allelopathic effects to the total weed inhibition. Six different cover crop species were combined with three weed species in the presence or absence of active carbon over a period of four weeks. Active carbon was used as an adsorbent for allelopathic substances in the soil. Our study revealed that the competition between cover crops and weeds shifted, possibly due to the minimisation of allelopathic effects by active carbon in the soil. We assume that the degree of cover crops allelopathic effects on weeds is species‐specific, both on the side of cover crops and on the weed side. The cover crops Raphanus sativus, Fagopyrum esculentum and Avena strigosa showed the highest allelopathic weed suppression with up to 28%. Additionally, Stellaria media turned out to be the most sensitive weed against allelopathic effects induced by all cover crops, except for Linum usitatissimum and Guizotia abyssinica. The knowledge about the contribution of competitive and allelopathic effects by cover crops would help to create cover crop mixtures with high weed suppressive ability. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: A field‐evolved herbicide‐resistant weed population can represent a heterogeneous composite of subpopulations that differ in their susceptibility and responsiveness to herbicide hormesis. Variable hormesis responsiveness can result in selection for and against certain subpopulations under low herbicide doses, and this has the potential to contribute to the evolution of resistance. The relevance of this hypothesis at practical field rates was studied for two field‐collected acetyl‐coenzyme A carboxylase (ACCase) target‐site resistant (TSR) biotypes of Alopecurus myosuroides Huds. (haplotype Leu1781) exposed to three ACCase inhibitors. Herbicide dose responses were evaluated at the population level and at different subpopulation levels after the dissection of individual plants by herbicide selection and genotyping. RESULTS: The practical field rates of fenoxaprop‐P were lower than the observed hormetic doses in the resistant subpopulation, whereas the field rates of clodinafop and cycloxydim stimulated the shoot biomass in different resistant subpopulations by 21–38% above that of the control. Because variable dose levels induced hormesis in the different subpopulations, the practical field rates showed a significant potential to selectively enhance parts of a resistant field population, but did not impact or adversely affect other parts of the population. CONCLUSION: As a consequence of population heterogeneity, herbicide hormesis may impact resistance evolution in weeds at realistic use rates via the selective promotion of individual genotypes. However, the practical relevance of this phenomenon may be influenced by many factors, such as the herbicidal active ingredient used, as indicated in this study. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: The sustainable management of unwanted vegetation in agricultural fields through integrated weed control strategies requires detailed knowledge about the maternal formation of primary seed dormancy, to support the prediction of seedling emergence dynamics. This knowledge is decisive for the timing of crop sowing and nonchemical weed control measures. Studies in controlled environments have already demonstrated that thermal conditions and, to some extent, water availability during seed set and maturation has an impact on the level of dormancy. However, it is still unclear if this applies also under field conditions, where environmental stressors and their timing are more variable. We address this question for Alopecurus myosuroides in south‐western Sweden. We quantified the effects of cumulated temperature and precipitation as well as soil water potential during the reproductive growth phase of A myosuroides on primary seed dormancy under field conditions. Empirical models differing in focal time intervals and, in case of soil water potential, focal soil depths were compared regarding their predictive power. The highest predictive power for the level of primary dormancy of A. myosuroides seeds was found for a two‐factorial linear model containing air temperature sum between 0 and 7 days before peak seed shedding as well as the number of days with soil water potential below field capacity between 7 and 35 days before peak seed shedding. For soil water potential, it was found that only the top 10 cm soil layer is of relevance, which is in line with the shallow root architecture of A. myosuroides. We conclude that for this species the level of dormancy depends on the magnitude and timing of temperature and water availability during the reproductive growth phase. Water availability appears to be more important during maternal environmental perception and temperature during zygotic environmental perception. [ABSTRACT FROM AUTHOR]

Summary: The distribution of Alopecurus myosuroides (black‐grass) in fields is patchy. The locations of these patches can be influenced by the environment. This presents an opportunity for precision management through patch spraying. We surveyed five fields on various types of soil using a nested sampling design and recorded both A. myosuroides seedlings in autumn and seed heads in summer. We also measured soil properties at those sampling locations. We found that the patches of seed heads within a field were smaller than the seedling patches, suggesting that techniques for patch spraying based on maps of heads in the previous season could be inherently risky. We also found that the location of A. myosuroides patches within fields can be predicted through their relationship with environmental properties and that these relations are consistent across fields on different soil types. This improved understanding of the relations between soil properties and A. myosuroides seedlings could allow farmers to use pre‐existing or suitably supplemented soil maps already in use for the precision application of fertilisers as a starting point in the creation of herbicide application maps. [ABSTRACT FROM AUTHOR]

BACKGROUND: The efficacy of pre-emergence herbicides within fields is spatially variable as a consequence of soil heterogeneity. We quantified the effect of soil organic matter on the efficacy of two pre-emergence herbicides, flufenacet and pendimethalin, against Alopecurusmyosuroides and investigated the implications of variation in organic matter for weed management using a crop-weed competition model. RESULTS: Soil organic matter played a critical role in determining the level of control achieved. The high organicmatter soil had more surviving weeds with higher biomass than the low organic matter soil. In the absence of competition, surviving plants recovered to produce the same amount of seed as if no herbicide had been applied. The competition model predicted that weeds surviving pre-emergence herbicides could compensate for sublethal effects even when competing with the crop. The ED50 (median effective dose) was higher for weed seed production than seedling mortality or biomass. This difference was greatest on high organic matter soil. CONCLUSION: These results showthat the application rate of herbicides should be adjusted to account for within-field variation in soil organic matter. The results from the modelling emphasised the importance of crop competition in limiting the capacity of weeds surviving pre-emergence herbicides to compensate and replenish the seedbank. [ABSTRACT FROM AUTHOR]

Summary: Mapping weed densities within crops has conventionally been achieved either by detailed ecological monitoring or by field walking, both of which are time‐consuming and expensive. Recent advances have resulted in increased interest in using Unmanned Aerial Systems (UAS) to map fields, aiming to reduce labour costs and increase the spatial extent of coverage. However, adoption of this technology ideally requires that mapping can be undertaken automatically and without the need for extensive ground‐truthing. This approach has not been validated at large scale using UAS‐derived imagery in combination with extensive ground‐truth data. We tested the capability of UAS for mapping a grass weed, Alopecurus myosuroides, in wheat crops. We addressed two questions: (i) can imagery accurately measure densities of weeds within fields and (ii) can aerial imagery of a field be used to estimate the densities of weeds based on statistical models developed in other locations? We recorded aerial imagery from 26 fields using a UAS. Images were generated using both RGB and Rmod (Rmod 670–750 nm) spectral bands. Ground‐truth data on weed densities were collected simultaneously with the aerial imagery. We combined these data to produce statistical models that (i) correlated ground‐truth weed densities with image intensity and (ii) forecast weed densities in other fields. We show that weed densities correlated with image intensity, particularly Rmod image data. However, results were mixed in terms of out of sample prediction from field‐to‐field. We highlight the difficulties with transferring models and we discuss the challenges for automated weed mapping using UAS technology. [ABSTRACT FROM AUTHOR]

Glyphosate use in the United Kingdom has more than doubled in the last 20 years. Much of this increase is driven by efforts to control herbicide resistant weeds, particularly Alopecurus myosuroides, prior to crop drilling. There is precedent for evolution of glyphosate resistance in similar situations, raising concerns over the sustainability of glyphosate use in the UK. We used dose-response experiments to examine variation in glyphosate sensitivity amongst 40 field-collected A. myosuroides populations. No populations were resistant to glyphosate, but ED90 values ranged between 354 and 610 g a.i. ha−1. Five populations had ED90 values significantly higher than the unexposed control population collected from a site at Rothamsted Research with no previous glyphosate exposure. Recurrent selection experiments were performed to determine whether variation in glyphosate sensitivity had a heritable basis. Following two rounds of selection, five of six field populations evolved significantly reduced sensitivity to glyphosate, with R/S ratios, based on estimated ED50 values, ranging from 1.2 to 1.5. These results confirm that there is a heritable basis to variation in glyphosate sensitivity. The response to selection was modest. Evolved populations were not highly resistant to glyphosate, although some twice-selected individuals survived recommended field rates. These results do not represent definitive proof of the potential of A. myosuroides to evolve glyphosate resistance, although they do indicate caution is needed when considering the sustainability of increased glyphosate use to control this herbicide resistance-prone species. [ABSTRACT FROM AUTHOR]

Herbicide resistance in Alopecurus myosuroides causes severe problems in Western European cropping systems. Costs of herbicide resistance were investigated in this study by analysing variable production costs and sales revenues. Three farms were selected for this study, with winter wheat as the dominating crop in all farms. Resistance in A. myosuroides populations was verified at all locations. Four farming approaches were simulated over a period of 20 years: (i) continuing the actual cropping system without increase of resistance, (ii) continuing the actual cropping system with increase of resistance, (iii) changing cropping practice to overcome resistance and (iv) changing cropping practice to prevent resistance. Contribution margins representing the proportion of sales revenue that is not consumed by variable costs were calculated for all approaches. Comparative static simulations showed that average contribution margins in a cropping system with more than 60% winter cereals and reduced tillage practice dropped from 807 € ha−1 a−1 without herbicide resistance to 307 € ha−1 a−1 with herbicide resistance. Alopecurus myosuroides population densities increased to more than 1000 plants m−2. Diverse crop rotations, including spring crops, clover-grass leys and intensive tillage, suppressed A. myosuroides populations, and average contribution margin was 630 € ha−1 a−1. Preventive methods with rotations of winter cereals and spring crops with less clover-grass leys resulted in an average contribution margin of 691 € ha−1 a−1. In conclusion, rotations of winter cereals and spring crops combined with inversion tillage and herbicides provide stable yields and can prevent weed population increase. [ABSTRACT FROM AUTHOR]

BACKGROUND Managing herbicide-resistant weeds is becoming increasingly difficult. Here we adapted the weed dynamics model Alomy Sys to account for experimentally measured fitness costs linked to mutants of target-site resistance to acetyl-coenzyme A carboxylase ( ACCase)-inhibiting herbicides in Alopecurus myosuroides. We ran simulations to test how effectively cultural practices manage resistance. RESULTS Simulations of an oilseed rape/winter wheat/winter barley rotation showed that, when replacing one of the seven applied herbicides with an ACCase-inhibiting one, resistant mutants exceeded 1 plant m−2, with a probability of 40%, after an average of 18 years. This threshold was always exceeded when three or four ACCase-inhibiting herbicides were used, after an average of 8 and 6 years respectively. With reduced herbicide rates or suboptimal spraying conditions, resistance occurred 1-3 years earlier in 50% of simulations. Adding spring pea to the rotation or yearly mouldboard ploughing delayed resistance indefinitely in 90 and 60% of simulations respectively. Ploughing also modified the genetic composition of the resistant population by selecting a previously rare mutant that presented improved pre-emergent growth. The prevalence of the mutations was influenced more by their associated fitness cost or benefit than by the number of ACCase-inhibiting herbicides to which they conferred resistance. CONCLUSION Simulations allowed us to rank weed management practices and suggest that pleiotropic effects are extremely important for understanding the frequency of herbicide resistance in the population. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Weeds tend to aggregate in patches within fields, and there is evidence that this is partly owing to variation in soil properties. Because the processes driving soil heterogeneity operate at various scales, the strength of the relations between soil properties and weed density would also be expected to be scale-dependent. Quantifying these effects of scale on weed patch dynamics is essential to guide the design of discrete sampling protocols for mapping weed distribution. We developed a general method that uses novel within-field nested sampling and residual maximum-likelihood ( reml) estimation to explore scale-dependent relations between weeds and soil properties. We validated the method using a case study of Alopecurus myosuroides in winter wheat. Using reml, we partitioned the variance and covariance into scale-specific components and estimated the correlations between the weed counts and soil properties at each scale. We used variograms to quantify the spatial structure in the data and to map variables by kriging. Our methodology successfully captured the effect of scale on a number of edaphic drivers of weed patchiness. The overall Pearson correlations between A. myosuroides and soil organic matter and clay content were weak and masked the stronger correlations at >50 m. Knowing how the variance was partitioned across the spatial scales, we optimised the sampling design to focus sampling effort at those scales that contributed most to the total variance. The methods have the potential to guide patch spraying of weeds by identifying areas of the field that are vulnerable to weed establishment. [ABSTRACT FROM AUTHOR]

Non-target-site resistance ( NTSR) comprises a set of mechanisms conferring resistance to multiple modes of action. Investigation of the number of loci involved in NTSR will aid in the understanding of these resistance mechanisms. Therefore, six different multiple herbicide-resistant Alopecurus myosuroides plants with different herbicide history were crossed in two generations with a susceptible wild type. Seeds from the backcrossing generation were studied for their segregation rate for resistance to five herbicides with four different modes of action ( HRAC groups C2, A, B and K3). Taking into account that NTSR is a set of quantitative traits, the numbers of loci controlling NTSR were estimated using a normal mixture model fitted by the NLMIXED procedure of SAS. Each herbicide was controlled by a different number of loci comparing the six plants. In most of the cases, chlorotoluron resistance was controlled by one locus, whereas resistance to fenoxaprop-P-ethyl needed one or two loci. Resistance to pinoxaden was in all plants conferred by two loci. Cross-resistance of fenoxaprop-P-ethyl and pinoxaden was found in all backcrossings, indicating that at least one of the two loci is responsible for both resistances. Resistance to mesosulfuron + iodosulfuron was conferred by a minimum of two loci. Results indicated that a minimum of five different loci can be involved in a multiple NTSR plant. Furthermore, the plant-specific accumulation of NTSR loci was demonstrated. Such behaviour should be taken into account when evaluating the development and further spread of herbicide resistance. [ABSTRACT FROM AUTHOR]

Two hundred and twenty weed species have evolved resistance to one or more herbicides, and there are now 404 unique cases (species × site of action) of herbicide-resistant weeds globally. ALS inhibitor-resistant weeds account for about a third of all cases (133/404) and are particularly troublesome in rice and cereals. Although 71 weed species have been identified with triazine resistance, their importance has dwindled with the shift towards Roundup Ready® crops in the USA and the reduction of triazine usage in Europe. Forty-three grasses have evolved resistance to ACCase inhibitors, with the most serious cases being Avena spp., Lolium spp., Phalaris spp., Setaria spp. and Alopecurus myosuroides, infesting more than 25 million hectares of cereal production globally. Of the 24 weed species with glyphosate resistance, 16 have been found in Roundup Ready® cropping systems. Although Conyza canadensis is the most widespread glyphosate-resistant weed, Amaranthus palmeri and Amaranthus tuberculartus are the two most economically important glyphosate-resistant weeds because of the area they infest and the fact that these species have evolved resistance to numerous other herbicide sites of action, leaving growers with few herbicidal options for their control. The agricultural chemical industry has not brought any new herbicides with novel sites of action to market in over 30 years, making growers reliant on using existing herbicides in new ways. In addition, tougher registration and environmental regulations on herbicides have resulted in a loss of some herbicides, particularly in Europe. The lack of novel herbicide chemistries being brought to market combined with the rapid increase in multiple resistance in weeds threatens crop production worldwide. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Due to the steadily increasing number of putative herbicide-resistant weed populations, the demand for rapid in-season tests is rising. In this study, we introduce a new quantitative herbicide-resistance test system based on chlorophyll fluorescence imaging analysis of photosynthesis-related parameters. Susceptible and herbicide-resistant populations of Alopecurus myosuroides (black-grass) were cultivated in multiwell tissue culture plates containing nutrient agar and different dosages of fenoxaprop- P-ethyl and mesosulfuron+iodosulfuron. The maximum quantum efficiency of the PSII was measured 3 h after transplanting ( HAT) and then for seven days every 24 h. Data of maximum quantum efficiency of the PSII were compared with standard whole-plant pot tests and molecular tests for target-site mutations. It was possible to fit dose-response curves and calculate corresponding resistance factors for ED90 for all populations tested using the chlorophyll fluorescence imaging. It was possible to distinguish between resistant and susceptible populations. The results of the chlorophyll fluorescence imaging corresponded well with the standard whole-plant pot tests in the glasshouse. However, populations with proved target-site mutations did not differ from other herbicide-resistant populations in the maximum quantum efficiency values of the PSII. We conclude that the chlorophyll fluorescence imaging provides reliable data on herbicide resistance for both modes of action tested in a shorter time and using less space, compared with standard whole-plant pot tests in the glasshouse. [ABSTRACT FROM AUTHOR]

This study reviews 52 field experiments, mostly from the UK, studying the effects of cultivation techniques, sowing date, crop density and cultivar choice on Alopecurus myosuroides infestations in cereal crops. Where possible, a statistical meta-analysis has been used to calculate average responses to the various cultural practices and to estimate their variability. In 25 experiments, mouldboard ploughing prior to sowing winter cereals reduced A. myosuroides populations by an average of 69%, compared with non-inversion tillage. Delaying drilling from September to the end of October decreased weed plant densities by approximately 50%. Sowing wheat in spring achieved an 88% reduction in A. myosuroides plant densities compared with autumn sowing. Increasing winter wheat crop density above 100 plants m−2 had no effect on weed plant numbers, but reduced the number of heads m−2 by 15% for every additional increase in 100 crop plants, up to the highest density tested (350 wheat plants m−2). Choosing more competitive cultivars could decrease A. myosuroides heads m−2 by 22%. With all cultural practices, outcomes were highly variable and effects inconsistent. Farmers are more likely to adopt cultural measures and so reduce their reliance on herbicides, if there were better predictions of likely outcomes at the individual field level. [ABSTRACT FROM AUTHOR]

BACKGROUND Target-site resistance to ALS- and ACCase-inhibiting herbicides in the grass weed Alopecurus myosuroides is associated with well-characterised allelic variants encoding ALS- and ACCase-based resistance. The potential for combined ALS and ACCase resistance presents a threat to future control, given the extent to which these herbicides are used. The authors present a primer extension method for rapid detection of known resistance-conferring substitutions. RESULTS Individuals showing combined resistance to field-rate mesosulfuron + iodosulfuron and cycloxydim were identified in four field-collected populations, with proportions ranging from 30 to 100%. Genotyping with the SNaPshot primer extension kit showed the T197 and L574 ALS and L1781 ACCase isoforms to be associated with ALS and ACCase resistance whenever they occurred. CONCLUSION Combined ALS and ACCase target-site resistance threatens future control of A. myosuroides. The SNaPshot extension assay provides a reliable new multiplexable method for characterising known allelic variants of the ALS and ACCase genes of A. myosuroides. The method offers significant advantages over both CAPS/ dCAPS and PASA in that full genotyping can be accomplished at any nucleotide position using a single extension primer. © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Predicting the impact of climate change on the damage niche of an agricultural weed at a local scale requires a process-based modelling approach that integrates local environmental conditions and the differential responses of the crop and weed to change. A simulation model of the growth and population dynamics of winter wheat and a competing weed, Sirius 2010, was calibrated and validated for the most economically damaging weed in UK cereals, Alopecurus myosuroides. The model was run using local-scale climatic scenarios generated by the LARS- WG weather generator and based on the HadCM3 projections for the periods 2046-2065 and 2080-2099 to predict the impact of climate change on the population dynamics of the weed and its effect on wheat yields. Owing to rising CO2 concentration and its effect on radiation use efficiency of wheat, weed-free wheat yields were predicted to increase. The distribution of the weed was predicted to remain broadly similar with a possible northward shift in range. Local-scale variation in the impact of climate change was apparent owing to variation in soil type and water holding capacity. The competitive balance was shifted in favour of the deeper rooted crop under climate change, particularly on sites with lighter soils, owing to more frequent and severe drought stress events. Although the damage niche of A. myosuroides was predicted to reduce under climate change, it is likely that weeds with contrasting physiology, such as C4 species, will be better adapted to future conditions and pose a more serious threat. [ABSTRACT FROM AUTHOR]

Makowski D, Chauvel B & Munier-Jolain N (2010). Improving a weed population model using a sequential Monte Carlo method. Weed Research 50, 373–382. Field measurements and weed population model predictions have been proposed as the basis for recommendations on the need for chemical or mechanical treatment, but both approaches have some limitations. This study shows how a Sequential Monte Carlo (SMC) method can be used to combine weed count measurements and model predictions, to derive a better estimate of weed population characteristics. SMC was applied to a dynamic model simulating weed densities, seed production and seedbank densities for Alopecurus myosuroides (blackgrass). The benefit resulting from SMC was quantified for several types of weed count data, using experiments carried out in seven plots during 6 years. Compared with the initial model predictions, SMC reduced the root mean squared error (RMSE) by 33.5–81.5%. Compared with the weed densities derived from the weed counts alone, SMC reduced the RMSE by 1.2–10%. SMC should be preferred to the single use of model or of weed count data, because it can improve weed density predictions and because the probability distributions computed by SMC can be used to analyse the uncertainty about the state of the system. [ABSTRACT FROM AUTHOR]

Persistence of seeds of the four winter annual grass species, Alopecurus myosuroides, Bromus sterilis, Bromus hordeaceus and Vulpia myuros, were studied under field conditions. The studies also included the two dicotyledon species, Tripleurospermum inodorum and Galium aparine. Seed samples were stored in the field at different depths in the plough layer for a year. Following germination, seedling emergence was taken as an indicator of field persistence. In a supplementary investigation, seed samples were placed on the soil surface or buried at 2 cm for a month and then tested for viability. Persistence of the two Bromus species was very short, irrespective of depth and duration of burial. Persistence of the other species was positively correlated with incorporation of seeds to a few centimetres depth. Increasing the depth of incorporation below 2 cm had a variable influence on persistence. Persistence of seeds placed directly on the soil surface was short, whether they were left there for a year or a month. Whether seeds at the soil surface were left uncovered or covered with chopped straw had limited influence on seed persistence. However, straw cover significantly increased persistence of A. myosuroides seeds and there was the same tendency with T. inodorum. [ABSTRACT FROM AUTHOR]

Pot and field tests were conducted to evaluate the efficacy of pyribenzoxim for winter weeds in wheat. In the pot tests, pyribenzoxim, at 50 g ha−1, controlled certain biotypes of blackgrass, including a fenoxaprop-P-ethyl-resistant biotype (the “Notts” biotype). A chlorotoluron-resistant blackgrass (the “Peldon” biotype) was not controlled. Cleaver, at the three-to-four-leaf stage, was completely controlled by pyribenzoxim at 30 g ha−1. In the field, the application in December gave good control of common chickweed, but did not control other weeds. No damage to wheat was observed with this rate of pyribenzoxim in December. The application in March gave complete control of blackgrass , hairy chess, and soft brome at 70 g ha−1, and cleaver at 140 g ha−1. The partial control of corn poppy and field violet was achieved. The March application scorched the wheat at 50–70 g ha−1, with prolonged stunting at 100–140 g ha−1. In conclusion, it was shown that pyribenzoxim had potential as a wheat herbicide, but needed further fine-tuning to find an optimum dosage. [ABSTRACT FROM AUTHOR]

Black-grass ( Alopecurus myosuroides) is an allogamous grass weed common in cereal fields of northern Europe, which developed resistance to a widely used family of herbicides, the ACCase-inhibiting herbicides. Resistance is caused by mutations at the ACCase gene and other, metabolism-based, mechanisms. We investigated the genetic structure of 36 populations of black-grass collected in one region of France (Côte d’Or), using 116 amplified fragment length polymorphism (AFLP) loci and sequence data at the ACCase gene. The samples were characterized for their level of herbicide resistance and genotyped for seven known ACCase mutations conferring resistance. All samples contained herbicide-resistant plants, and 19 contained ACCase mutations. The genetic diversity at AFLP loci was high ( HT = 0.246), while differentiation among samples was low ( FST = 0.023) and no isolation by distance was detected. Genetic diversity within samples did not vary with the frequency of herbicide resistance. A Bayesian algorithm was used to infer population structure. The two genetic clusters inferred were not associated with any geographical structure or with herbicide resistance. A high haplotype diversity ( Hd = 0.873) and low differentiation ( GST = 0.056) were observed at ACCase. However, haplotype diversity within samples decreased with the frequency of ACCase-based resistance. We suggest that the genetic structure of black-grass is affected by its recent expansion as a weed. Our data demonstrate that the strong selection imposed by herbicides did not modify the genome-wide genetic structure of an allogamous weed that probably has large effective population sizes. Our study gives keys to a better understanding of the evolution of successful, noxious weeds in modern agriculture. [ABSTRACT FROM AUTHOR]

• Effective herbicide resistance management requires an assessment of the range of spatial dispersion of resistance genes among weed populations and identification of the vectors of this dispersion. • In the grass weed Alopecurus myosuroides (black-grass), seven alleles of the acetyl-CoA carboxylase ( ACCase) gene are known to confer herbicide resistance. Here, we assessed their respective frequencies and spatial distribution on two nested geographical scales (the whole of France and the French administrative district of Côte d’Or) by genotyping 13 151 plants originating from 243 fields. • Genetic variation in ACCase was structured in local populations at both geographical scales. No spatial structure in the distribution of resistant ACCase alleles and no isolation by distance were detected at either geographical scale investigated. • These data, together with ACCase sequencing and data from the literature, suggest that evolution of A. myosuroides resistance to herbicides occurred at the level of the field or group of adjacent fields by multiple, independent appearances of mutant ACCase alleles that seem to have rather restricted spatial propagation. Seed transportation by farm machinery seems the most likely vector for resistance gene dispersal in A. myosuroides. [ABSTRACT FROM AUTHOR]

We have investigated the process of evolution of target-site-based resistance to herbicides inhibiting acetyl-CoA carboxylase (ACCase) in nine French populations of black-grass (Alopecurus myosuroides Huds). To date, two different ACCase resistant alleles are known. One contains an isoleucine-to-leucine substitution at position 1781, the second contains an isoleucine-to-asparagine substitution at position 2041. Using phylogenetic analysis of ACCase sequences, we showed that [sup1781]Leu ACCase alleles evolved from four independent origins in the nine black-grass populations studied, while [sup2041]Asn ACCase alleles evolved from six independent origins. No geographical structure of black-grass populations was revealed. This implies that these populations, although geographically distant, are, or have until recently been, connected by gene flows. Comparison of biological data obtained from herbicide sensitivity bioassay and molecular data showed that distinct resistance mechanisms often exist in a single black-grass population. Accumulation of different resistance mechanisms in a single plant was also demonstrated. We conclude that large-scale evolution of resistance to herbicides in black-grass is a complex phenomenon, resulting from the independent selection of various resistance mechanisms in local black-grass populations undergoing contrasted herbicide and agronomical selection pressures, and connected by gene flows whose parameters remain to be determined. [ABSTRACT FROM AUTHOR]

The metabolism of chlorotoluron in whole plants and cell suspensions was investigated in a previously characterized chlorotoluron-resistant biotype of Alopecurus myosuroides Huds. Both resistant plants and cell suspensions showed a greater capability to metabolize chlorotoluron to non-phytotoxic compounds than the respective susceptible counterparts. Data revealed that although both biotypes degraded chlorotoluron by N-dealkylation and ring-methyl hydroxylation, the resistant biotype showed an enhanced capacity to hydroxylate the parent herbicide. The cytochrome (Cyt) P450 inhibitor 1-aminobenzotriazole (ABT) inhibited the metabolism of chlorotoluron in both resistant and susceptible plants by reducing the formation of non-toxic aryl-hydroxylated derivatives and polar conjugates. N-demethylations were less susceptible to ABT than the other oxidative reactions, but this does not necessarily imply that the second detoxification activity is not Cyt P450, as some P450 activities are more susceptible to ABT than others. Ring-methyl hydroxylation inhibition affected the ability of resistant plants to recover photosynthetic activity after incubation in chlorotoluron, showing a similar fluorescence pattern to susceptible plants in the same conditions without ABT. Fluorescence and metabolism data strongly support the thesis of Cyt P450-mediated 4-methylphenyl hydroxylation as the main route of detoxification of chlorotoluron in the resistant biotype. [ABSTRACT FROM AUTHOR]

Herbicide-resistant populations of Alopecurus myosuroides Huds (black-grass) have become widespread throughout the UK since the early 1980s. Clear evidence suggests that more than one resistance mechanism exists, and glutathione S-transferases (GSTs) have been implicated in resistance due to enhanced metabolism. This study reports the determination of GST activity in four UK black-grass populations from field sites situated in the East Midlands. Data demonstrate that, as untreated plants in the field mature, there is an accompanying natural elevation of GST activity with natural environmental changes from winter to spring. We speculate that this endogenous change in enzyme activity with plant development in the field contributes to reduced efficacyof some graminicides applied in the spring. These observations are discussed in relation to predicting herbicide efficacy to achieve maximum control of this important grass weed. [ABSTRACT FROM AUTHOR]

Summary 1. We report on a 3-year field study designed to monitor the detailed population dynamics of Anisantha sterilis in winter wheat, as well as to explore the consequences of changing broad-scale patterns of management, in the form of reduced fertilizer inputs. 2. In the absence of herbicides, population dynamics were dominated by density-dependent population growth. Unusually, this occurred mainly through density-dependent recruitment. This was estimated to reduce population growth rates by 50-fold, compared with the effects of density-dependent competition between plants for resources. Density-dependent recruitment also tended to buffer populations against year-to-year variations in emergence levels. 3. Little evidence for temporal variations in allometric seed production, the strength of competition between plants for resources or maximal mean plant performance was found in this study, or in comparison with previously published data. 4. No aspect of the life cycle was significantly affected by variation in the level of applied nitrogen fertilizer. In the case of competitive interactions we postulate that this lack of effect results from reduced intraspecific competitive effects as a consequence of decreased maximal plant size under low nitrogen conditions. The highly competitive nature of the environment in which A. sterilis occurs means that such changes tend to mask the effects of changing nitrogen levels. 5. Estimates of the effects of cultivation, on the other hand, indicated that seed germination, and hence population growth, was reduced by up to 90% when ploughing was employed rather than minimum tillage. While to some extent the effects of variation in the form of cultivation on population numbers may be buffered by density-dependent recruitment, this effect outweighs any effects of nutrients or spatial or temporal variability in population dynamics. 6. Using previously published models for the dynamics of Alopecurus myosuroides, Avena sterilis and... [ABSTRACT FROM AUTHOR]