The impact of uptake, translocation and metabolism on the differential selectivity between blackgrass and wheat for the herbicide pyroxsulam

BACKGROUND: Wheat shows selectivity to pyroxsulam, a new broad‐spectrum herbicide with high activity on blackgrass. Studies were performed to establish whether uptake, translocation or metabolism were responsible for the differential activity in wheat compared with blackgrass. In addition, the effect of the safener cloquintocet‐mexyl on metabolism was evaluated in wheat and blackgrass shoots. RESULTS: Root uptake of pyroxsulam in blackgrass was significantly higher than in wheat, suggesting a possible activity enhancement in blackgrass owing to root uptake. Translocation to foliage from root uptake as well as translocation out of treated foliage following foliar applications was low in wheat compared with blackgrass, likely owing to the rapid metabolism of pyroxsulam in wheat. Wheat metabolized pyroxsulam significantly faster than blackgrass to the less active O‐dealkylation product. Wheat shoots metabolized pyroxsulam faster when the safener cloquintocet‐mexyl was present, but cloquintocet‐mexyl did not increase the rate of metabolism in blackgrass. CONCLUSIONS: The selectivity of pyroxsulam to wheat relative to blackgrass was connected primarily with differences in the rate of metabolism and generation of an inactive metabolite. Metabolism in wheat restricted subsequent movement of radioactivity out of the treated leaf. The rapid metabolism in wheat was increased by the addition of cloquintocet‐mexyl. Copyright © 2010 Society of Chemical Industry     

Practical experiences with a system for site-specific weed control in arable crops using real-time image analysis and GPS-controlled patch spraying

Information on temporal and spatial variation in weed seedling populations within agricultural fields is very important for weed population assessment and management. Primarily, spatial information allows a potential reduction in herbicide use, when post‐emergent herbicides are only applied to field sections with high weed infestation levels. This paper presents a system for site‐specific weed control in sugar beet, maize, winter wheat, winter barley, winter rape and spring barley. The system includes on‐line weed detection using digital image analysis, computer‐based decision making and Global Positioning System‐controlled patch spraying. In a 2‐year study, herbicide use with this map‐based approach was reduced in winter cereals by 6–81% for herbicides against broad leaved weeds and 20–79% for grass weed herbicides. Highest savings were achieved in cereals followed by sugar beet, maize and winter rape. The efficacy of weed control varied from 85% to 98%, indicating that site‐specific weed management will not result in higher infestation levels in the following crops.     

The action of herbicides on fatty acid biosynthesis and elongation in barley and cucumber

BACKGROUND: Herbicides that affect lipid metabolism have been used commercially for many years. Here, napropamide, diphenamid, dimethachlor and cafenstrole are compared; these have all been classified by the Herbicide Resistance Action Committee (HRAC) as K₃ herbicides and inhibitors of cell division and/or synthesis of very‐long‐chain fatty acids (VLCFAs). In addition, spiro‐decanedione A and pinoxaden dione are compared as inhibitors of lipid synthesis through inhibition of acetyl‐CoA carboxylase (ACCase). RESULTS: Whereas the chloracetamide dimethachlor and the carboxyamide cafenstrole potently inhibited VLCFA synthesis in both barley and cucumber, the acetamides napropamide and diphenamid which are also classified as K₃ herbicides and likewise the unclassified herbicide cinmethylin did not. The graminicide pinoxaden dione inhibited de novo fatty acid synthesis in barley, but not in cucumber, and correspondingly inhibited the plastid form of maize ACCase much more than the cytosolic form (IC₅₀ values of 0.1 and 17 µM ). By contrast, spiro‐decanedione A exhibited herbicidal effects not only on grasses but also on broad leaves, strongly inhibited maize cytosolic ACCase and inhibited synthesis of VLCFAs in cucumber. CONCLUSIONS: The acetamides napropamide and diphenamid, which do not inhibit VLCFA synthesis, should be classified separately from K₃ herbicides that do. Pinoxaden dione and spiro‐decanedione A represent new classes of chemicals acting on plant lipid synthesis. Copyright © 2010 Society of Chemical Industry     

Real-time weed detection, decision making and patch spraying in maize, sugarbeet, winter wheat and winter barley

Information on temporal and spatial variation in weed seedling populations within agricultural fields is very important for weed population assessment and management. Most of all, it allows a potential reduction in herbicide use, when post‐emergence herbicides are only applied to field sections with weed infestation levels higher than the economic weed threshold; a review of such work is provided. This paper presents a system for site‐specific weed control in sugarbeet (Beta vulgaris L.), maize (Zea mays L.), winter wheat (Triticum aestivum L.) and winter barley (Hordeum vulgare L.), including online weed detection using digital image analysis, computer‐based decision making and global positioning systems (GPS)‐controlled patch spraying. In a 4‐year study, herbicide use with this map‐based approach was reduced in winter cereals by 60% for herbicides against broad‐leaved weeds and 90% for grass weed herbicides. In sugarbeet and maize, average savings for grass weed herbicides were 78% in maize and 36% in sugarbeet. For herbicides against broad‐leaved weeds, 11% were saved in maize and 41% in sugarbeet.     

Allelic variation of the ACCase gene and response to ACCase-inhibiting herbicides in pinoxaden-resistant Lolium spp

BACKGROUND: The repeated use of acetyl‐coenzyme A carboxylase (ACCase) inhibiting herbicides to control grass weeds has selected for resistance in Lolium spp. populations in Italy. The efficacy of pinoxaden, a recently marketed phenylpyrazoline herbicide, is of concern where resistance to ACCase inhibitors has already been ascertained. ACCase mutations associated with pinoxaden resistance were investigated, and the cross‐resistance pattern to clodinafop, haloxyfop, sethoxydim, clethodim and pinoxaden was established on homo/heterozygous plants for four mutant ACCase alleles. RESULTS: Seven different mutant ACCase alleles (1781‐Leu, 1999‐Leu, 2041‐Asn, 2041‐Val, 2078‐Gly, 2088‐Arg and 2096‐Ala) and 13 combinations with two types of mutation were detected in the pinoxaden‐resistant plants. The 1781‐Leu allele appears to confer a dominant resistance to pinoxaden, clodinafop, haloxyfop, sethoxydim and clethodim at 60 g AI ha^?1. The 2041‐Asn and 2041‐Val alleles are associated with dominant or partially dominant resistance to FOPs, no substantial resistance to DIMs and a moderate resistance to pinoxaden. The 2088‐Arg allele endows a partially dominant resistance to clodinafop, sethoxydim and most likely to pinoxaden. In addition, non‐target‐site resistance mechanisms seem to be involved in pinoxaden resistance. CONCLUSION: Almost all the ACCase mutations selected in the field by other ACCase inhibitors are likely to confer resistance to pinoxaden. Although pinoxaden is sometimes able to control FOP‐resistant populations, it should not be considered as a sustainable ACCase resistance management tool. The presence of non‐ACCase‐based resistance mechanisms that could confer resistance to herbicides with different modes of action further complicates the resistance management strategies. Copyright © 2011 Society of Chemical Industry     

麦田入侵杂草小籽虉草对麦田常用除草剂的敏感性测定

为筛选能有效防除云南麦田入侵杂草小籽虉草Phalaris minor的除草剂, 采用温室盆栽法分别测定了麦田常用7种茎叶处理剂各7个梯度剂量对小籽虉草的毒力?结果表明, 在推荐剂量下, 50%异丙隆WP?5%唑啉草酯EC?15%炔草酯WP?69 g/L精噁唑禾草灵EW?7.5%啶磺草胺WG?30 g/L甲基二磺隆OD和70%氟唑磺隆WG对小籽虉草药后30 d的株防效分别为99.34%?99.43%?87.50%?75.00%?34.50%?37.50%, 54.17%, 药后30 d的鲜重防效分别为87.92%?92.66%?56.09%?74.43%?57.17%?45.61%?44.67%?所有除草剂中, 唑啉草酯的GR90接近推荐使用剂量的90%?异丙隆的GR90略高于推荐剂量, 其他除草剂的GR90远高于麦田推荐使用剂量?以上结果表明, 防治麦田杂草小籽虉草的首选除草剂为唑啉草酯, 备选除草剂种类少?     

Prevalence of cross‐ or multiple resistance to the acetyl‐coenzyme A carboxylase inhibitors fenoxaprop,clodinafop and pinoxaden in black‐grass (Alopecurus myosuroides Huds.) in France

BACKGROUND: Repeated use of acetyl‐CoA carboxylase (ACCase) inhibitors, especially fenoxaprop and clodinafop, since the late 1980s has selected for resistance in Alopecurus myosuroides Huds. (black‐grass) in France. We investigated whether resistance to pinoxaden, a phenylpyrazoline ACCase inhibitor to be marketed in France, was present in French black‐grass populations. We investigated pinoxaden resistance conferred by five mutant ACCase isoforms. Using 84 French black‐grass field samples, we also compared the frequencies of other mechanisms endowing resistance to fenoxaprop, clodinafop or pinoxaden. RESULTS: ACCase mutant isoforms Leu‐1781, Gly‐2078 and, likely, Cys‐2027 conferred cross‐resistance to pinoxaden, while isoform Asn‐2041 possibly conferred moderate resistance. Other mechanisms of resistance to fenoxaprop, clodinafop and pinoxaden were detected in 99, 68 and 64% of the samples investigated, respectively. Cross‐ or multiple resistance to fenoxaprop or clodinafop and pinoxaden was not systematically observed, suggesting a diversity of mechanisms exist. CONCLUSION: Pinoxaden resistance was observed before pinoxaden release in France. Only a fraction of the mechanisms endowing fenoxaprop or clodinafop resistance also confer pinoxaden resistance. Pinoxaden resistance was likely mostly selected for by ACCase inhibitors, and, in some cases, possibly by herbicides with other modes of action. This illustrates the necessity to use metabolisable herbicides cautiously where black‐grass has evolved non‐target‐site‐based resistance. Copyright © 2009 Society of Chemical Industry     

Cross‐resistance patterns to acetyl coenzyme A carboxylase (ACCase) inhibitors associated with different ACCase mutations in Beckmannia syzigachne

Beckmannia syzigachne (American sloughgrass) is a competitive grass weed found in China. Fenoxaprop‐P‐ethyl is widely used for control of this species in China. Resistance to fenoxaprop‐P‐ethyl in B. syzigachne has been reported to be conferred by an isoleucine(Ile)‐1781‐leucine(Leu) substitution in the gene encoding the herbicide target, acetyl‐CoA carboxylase (ACCase). In this study, three mutations were detected by derived cleaved amplified polymorphic sequence (dCAPS) method in fenoxaprop‐P‐ethyl‐resistant B. syzigachne populations: Ile‐1781‐Leu in population JCWL‐R, Ile‐2041‐Asn in JCJT‐R and Gly‐2096‐Ala in JYJD‐R. The data indicated they were genetically homogeneous (homozygous mutant) at the ACCase locus. The use of cytochrome P450 inhibitors was shown to slightly reduce the GR₅₀ value of fenoxaprop‐P‐ethyl‐resistant populations, from which we inferred a combination of target‐site resistance (TSR) and non‐target‐site resistance (NTSR) was involved in fenoxaprop‐P‐ethyl‐resistance. We characterised the cross‐resistance patterns to ACCase inhibitors in B. syzigachne. The plants in the JCWL‐R population were highly resistant to all tested APPs (aryloxyphen‐oxypropionates), sethoxydim and pinoxaden, and moderately resistant to clethodim. The plants in the JCJT‐R population were highly resistant to fluazifop‐P‐butyl, clodinafop‐propargyl, cyhalofop‐butyl, metamifop and pinoxaden; moderately resistant to haloxyfop‐R‐methyl, quizalofop‐P‐ethyl and sethoxydim; and sensitive to clethodim. The plants in the JYJD‐R population were highly resistant to clodinafop‐propargyl, metamifop and pinoxaden; moderately resistant to haloxyfop‐R‐methyl, cyhalofop‐butyl, quizalofop‐P‐ethyl, fluazifop‐P‐butyl and sethoxydim; and sensitive to clethodim. If resistance to ACCase inhibitors is present in B. syzigachne populations in the field, then our results indicate that clethodim should be used. While we demonstrated the cross‐resistance patterns of TSR resulting from three mutations in B. syzigachne, we also demonstrated that NTSR plays a role in resistance, which will complicate weed management.     

Interactions between the tillage system and crop rotation on the crop yield and weed populations under arid conditions

Field experiments were conducted in Iran in order to determine the interactions between the tillage system and crop rotation on weed seedling populations and crop yields from 2002 to 2005. No tillage, shallow tillage and deep tillage were the main plots and three crop sequences comprising continuous wheat (W‐W), wheat–canola–wheat–canola (C‐W) and wheat–safflower–wheat–safflower (S‐W) were the subplots. Bromus japonicus, Carthumus lanatus, Polygonum aviculare, Lolium temulentum and Avena ludoviciana were found to be the dominant species. The initial weed population in 2002 was estimated at 65 seedlings per m² and B. japonicus (～35 seedlings per m²) was the most abundant species, followed by A. ludoviciana and L. temulentum. The dominant weed species mostly did not favor the combination of S‐W and C‐W with any tillage type. For the B. japonicus population, S‐W in combination with moldboard plowing indicated the lowest seedling population. In conclusion, the crop sequence in combination with tillage would help to control troublesome weed species. Safflower and canola were determined to be effective in reducing the grass weeds. The inclusion of these crops in rotation also increased the total revenue of the cropping systems because of the higher sale price of canola and safflower.     

Multiple herbicide resistance in littleseed canarygrass (Phalaris minor): A threat to wheat production in India

Littleseed canarygrass (Phalaris minor Retz.), a troublesome weed of wheat in India, has evolved multiple herbicide resistance across three modes of action: photosynthesis at the photosystem II site A, acetyl‐coA carboxylase (ACCase), and acetolactate synthase inhibition. The multiple herbicide‐resistant (MHR) populations had a low level of sulfosulfuron resistance but a high level of resistance to clodinafop and fenoxaprop (ACCase inhibitors). Some of the populations had GR₅₀ (50% growth reduction) values for clodinafop that were 11.7‐fold greater than that of the most susceptible population. The clodinafop‐resistant populations also showed a higher level of cross‐resistance to fenoxaprop (fop group) but a low level of cross‐resistance to pinoxaden (den group). Although clodinafop and pinoxaden are from two different chemical families (fop and den groups), their same site of action is responsible for cross‐resistance behavior. The populations that were resistant to four groups of herbicides (phenylureas, sulfonylurea, aryloxyphenoxypropionate, and phenylpyrazolin) were susceptible to the triazine (metribuzin and terbutryn) and dinitroaniline (pendimethalin) herbicides. The P. minor populations that were resistant to the aryloxyphenoxypropionate and phenylurea herbicides were effectively controlled by the sulfonylurea herbicide, sulfosulfuron. In the fields infested with P. minor that was resistant to clodinafop, a sulfosulfuron application (25 g ha^?1) increased the wheat yield by 99.2% over that achieved using the recommended rate of clodinafop (60 g ha^?1). However, the evolution of multiple resistance against the four groups is a threat to wheat production. To prevent the spread of MHR P. minor populations, as well as the extension of multiple resistance to new chemicals, concerted efforts in developing and implementing a sound, integrated weed management program are needed. The integrated approach, consisting of crop and herbicide rotation with cultural and mechanical weed control tactics, should be considered as a long‐term resistance management strategy that will help to sustain wheat productivity and farmers' income.     

浙沪小麦田杂草调查及优势杂草化学防除技术研究

为了明确浙沪小麦田杂草发生情况及优势杂草控制技术,采用唐氏五级目测法和随机取样计数法相结合的方法,对上海和浙江的116块冬小麦田杂草进行了抽样调查,同时采用盆栽试验和田间小区试验测定了7种除草剂对主要危害杂草的防效。结果表明,浙沪冬小麦田共调查到杂草43种,隶属于14科,其中菊科杂草种类最多,有10种,其次是禾本科杂草9种,再次是石竹科杂草5种。杂草群落组成以禾本科杂草为主,优势杂草为日本看麦娘Alopecurus japonicus Steud.、菵草Beckmannia syzigachne(Steud.) Fern.、棒头草Polypogon fugax Nees ex Steud.、硬草Sclerochloa dura(L.) Beauv.、早熟禾Poa annua L.、鹅肠菜Myosoton aquaticum(L.) Moench、救荒野豌豆Vicia sativa L.、猪殃殃Galium spurium L.和小藜Chenopodium ficifolium Smith。室内除草活性及田间药效试验结果表明,日本看麦娘可用15%炔草酯WP、5%唑啉草酯EC、30 g/L...     

Spatial patterns,species richness and cover in weed communities of organic and conventional no‐tillage spring wheat systems

Heterogeneous field conditions are ubiquitous throughout agricultural systems and have given rise to the practice of site‐specific management, in an effort to increase sustainability and/or homogenise growing conditions and thereby increase crop yields. The spatial pattern of weeds in conventional systems is widely accepted to be aggregated, but there have been no scientific studies regarding the spatial pattern of weed distribution in organic systems. Using a combination of aggregation measures and quadrat variance techniques, this study compared the spatial pattern of weed distribution in conventionally managed no‐tillage spring wheat fields to those of organically managed spring wheat fields. Per cent weed cover data (by species) were collected in the summers of 2005 and 2006 from transects located in conventional no‐tillage and organic spring wheat fields. Weed cover was aggregated in both the conventional and the organic systems, but the patterns of aggregation were different for the two systems. Conventional no‐tillage systems showed a patch/gap pattern, while organic systems showed multiple scales of patchiness with few gaps. These results suggest that processes causing aggregation in the two systems may be different and that site‐specific management may be applicable to organic systems as well as conventional spring wheat systems.     

Evaluating the potential of Unmanned Aerial Systems for mapping weeds at field scales: a case study with Alopecurus myosuroides

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 R_mod (R_mod 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 R_mod 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.     

Littleseed canarygrass (Phalaris minor) resistance to clodinafop‐propargyl in wheat fields in north‐western India: Appraisal and management

Littleseed canarygrass (～canarygrass) evolved populations that are resistant to isoproturon during the early 1990s in north‐western India. Clodinafop‐propargyl (～clodinafop) was recommended for controlling these populations. It has been used extensively in wheat for the last several years. Recently, poor or no control of canarygrass by clodinafop has been observed in large areas, which could be related to cross‐resistance or multiple resistance. This study was designed to test whether resistance has evolved in canarygrass populations against clodinafop and to explore control of the resistant populations with sulfosulfuron and pinoxaden. Among the 311 canarygrass populations that were tested, 86, 55 and 34 showed variable phytotoxicity (0–99%) due to 0.030, 0.060 and 0.120 kg ha^?1 clodinafop, respectively. Based on the resistance index, 11 populations were “highly resistant”, 60 were “resistant” and the rest (240) were “susceptible” to clodinafop. Five and six clodinafop‐resistant populations showed slight resistance to 0.0125 kg ha^?1 sulfosulfuron and 0.025 kg ha^?1 pinoxaden, respectively. But, sulfosulfuron at 0.025 and 0.050 kg ha^?1 and pinoxaden at 0.050 and 0.100 kg ha^?1 controlled all the canarygrass populations. Clodinafop used for 4 years increased the chance of resistance evolving, whereas its rotation with sulfosulfuron reduced the chance of resistance evolving. This study showed that considerable canarygrass populations have evolved a low‐to‐high degree of resistance against clodinafop. The further use of clodinafop would lead to the spread of resistance in larger areas through the dispersal of resistant seeds. Clodinafop should be replaced with 0.025 kg ha^?1 sulfosulfuron or 0.050 kg ha^?1 pinoxaden. Besides, where canarygrass has not evolved resistance, the yearly rotation of sulfosulfuron with clodanafop or pinoxaden might delay the evolution of resistance.     

一株高地芽胞杆菌D30202的抑草活性及作用机制初探

为开发新型微生物除草剂, 通过萌发袋法对嗜盐高地芽胞杆菌Bacillus altitudinis菌株D30202抑制杂草种子萌发和幼苗生长的活性进行测定?通过盆栽茎叶喷雾法对不同有机溶剂萃取物的杀草谱和作物安全性进行测定和评价, 并以自生油菜Brassica napus L.为供试杂草对活性菌株的抑草机理进行初探?结果表明, 嗜盐高地芽胞杆菌菌株D30202发酵液的正丁醇萃取物对十字花科杂草自生油菜的除草活性最为显著, 同时对青稞Hordeum vulgare var. coeleste?小麦Triticum aestivum L.表现出较高的安全性?而经正丁醇萃取物处理的自生油菜, 其丙二醛(MDA)含量及抗氧化酶(SOD?POD?CAT)活性呈持续下降趋势, 表明该菌株的抑草作用机理可能是通过影响光合作用等代谢过程实现的?综上所述, 高地芽胞杆菌D30202可开发为禾本科作物田十字花科杂草的生物除草剂?     

Increasing weed flora in Danish arable fields and its importance for biodiversity

A number of political initiatives have been implemented to meet growing concerns about negative side effects of the intensification of land‐use practice over the past 25 years. Declining species diversity and abundance and pollution of the environment have been reported worldwide. In order to assess the overall effect on wild flora of the changing management of arable land, national surveys are necessary. Surveys of the weed flora in Danish arable fields were conducted in 1987–89 and 2001–04. The frequency of common weed species in spring barley, spring rape, winter rye, winter wheat and grass leys was compared between time periods. Weed frequency increased overall during the interval. Species that are of particular importance as food sources for invertebrates and birds increased considerably in some of the crops. The frequency of some grass species increased remarkably, possibly because of increased areas of winter crops. Some perennial weeds also became more frequent, probably caused by less mechanical weed control and a reduction in the use of specific herbicides. The dominant weed species in 2001–04, with frequency higher than 10%, were largely the same as in 1987–89, but included three new species in 2001–04. Only a few species occurred less frequently in 2001–04 than in 1987–89 and only in some crops. As common weed species make up an important food reservoir for wildlife, new trends in the management of arable land in Denmark seem to have led to more biodiversity.     

Does yield loss due to weed competition differ between organic and conventional cropping systems?

High weed abundance in organic crops is thought to be a key factor contributing to the greater yield loss in organic as compared with conventional cropping systems. However, even with greater weed densities than conventional systems, some organic systems have yields comparable to conventional systems, suggesting that cropping systems might differ in yield loss due to weed competition. The diversity in soil nutrient resources due to diversity in crop rotations and variable inputs might enhance crop tolerance to weed competition. We assessed the long‐term effects of contrasting levels of crop rotations (low, medium and high diversity) on weed density, weed biomass and wheat yield loss in organic and no‐till conventional cropping systems using a microplot study within a long‐term cropping systems trial at Scott, Saskatchewan, Canada. Weed density and biomass were found to be four times higher in the organic systems than in the conventional systems. Under standard weed management practices, organic had 44% lower yield than the conventional system. Lower yields in organic, even without weed competition, suggest that the lower yields are due to low soil productivity rather than weed competition. No differences in yield loss were observed among the organic and conventional systems or among the diverse crop rotations. We conclude that the organic management practices and/or increased crop rotation diversity did not enhance yield or reduce yield loss due to weed competition, due to the factors associated with lower soil fertility.     

Integrated management of Bromus diandrus in dryland cereal fields under no‐till

As herbicides have limited effect in controlling Bromus diandrus in no‐till dryland cereal fields, the integration of chemical and cultural methods needs to be investigated. A field study was carried out in Lleida (Spain) during 2008–09, 2009–10 and 2010–11 seasons, in a no‐till winter cereal field integrating delayed crop sowing with herbicides in a barley–wheat–wheat rotation. Three crop sowing dates were considered: D1, mid‐October; D2, mid‐November; and D3, early December, and the herbicides mesosulfuron‐methyl plus iodosulfuron‐methyl‐sodium were applied in wheat. Weed density, cumulative emergence and fecundity were estimated for each sowing date. In all three seasons, a significant reduction in the cumulative emergence of B. diandrus as compared to D1 was observed in D2 (82.0, 97.5 and 98.1%) and D3 (80.8, 98.7 and 97.2%). In addition, a significant decrease in weed density and seed rain was observed across all sowing dates and seasons. The herbicide used in wheat was more effective under delayed sowing, due to lower weed density and presence of less developed weed seedlings. After three seasons, the populations of B. diandrus were completely depleted in D2 and D3. This study demonstrates the possibility of eliminating brome infestations in dryland cereal fields in no‐till systems through the integration of cultural and chemical strategies.     

Mechanical and cultural strategies to control Cirsium arvense in organic arable cropping systems

Infestation with Cirsium arvense in organic cropping is an increasing problem in many parts of Europe. Non‐chemical management strategies against C. arvense, based on cultivation tactics and/or different cutting regimes, have received very little attention for many years. This study presents results from four experiments, undertaken under organic growing conditions, on the effects of repeated mowing or hoeing during the first part of the growing season, used in combination with competition from a suppressive crop (grass/white clover mixture or red clover). The strategies were mainly aimed at diminishing the regenerative capacity of C. arvense and the effects were thus measured in the subsequent year in spring barley crops, in the absence of any weed control. In general, number of passes of mowing and hoeing linearly reduced the amount of aboveground C. arvense biomass in the subsequent year. Increased competition induced by the competitive crops further reduced C. arvense biomass. Differences in barley yield were explained by the amount of C. arvense biomass only in one experiment, where this weed was most abundant. Our results suggest that an acceptable level of C. arvense control can be achieved through an intensive hoeing or mowing campaign, within one growing season only. This may lead to increased crop yield in the subsequent year.     

An aspartate to glycine change in the carboxyl transferase domain of acetyl CoA carboxylase and non‐target‐site mechanism(s) confer resistance to ACCase inhibitor herbicides in a Lolium multiflorum population

BACKGROUND: The increasing use of ACCase‐inhibiting herbicides has resulted in evolved resistance in key grass weeds infesting cereal cropping systems worldwide. Here, a thorough and systematic approach is proposed to elucidate the basis of resistance to three ACCase herbicides in a Lolium multiflorum Lam. (Italian rye grass) population from the United Kingdom (UK24). RESULTS: Resistance to sethoxydim and pinoxaden was always associated with a dominant D2078G (Alopecurus myosuroides Huds. equivalent) target‐site mutation in UK24. Conversely, whole‐plant herbicide assays on predetermined ACCase genotypes showed very high levels of resistance to diclofop‐methyl for all three wild DD2078 and mutant DG2078 and GG2078 ACCase genotypes from the mixed resistant population UK24. This indicates the presence of other diclofop‐methyl‐specific resistance mechanism(s) yet to be determined in this population. The D2078G mutation could be detected using an unambiguous DNA‐based dCAPS procedure that proved very transferable to A. myosuroides, Avena fatua L., Setaria viridis (L.) Beauv. and Phalaris minor Retz. CONCLUSION: This study provides further understanding of the molecular basis of resistance to ACCase inhibitor herbicides in a Lolium population and a widely applicable PCR‐based method for monitoring the D2078G target‐site resistance mutation in five major grass weed species. Copyright © 2010 Society of Chemical Industry