The effects of water management,timing and the rate of several herbicides on the growth of Murdannia keisak (Hassk.) Handel-Mazz

Murdannia keisak is a competitive rice weed found throughout the world. The aims of this study were to investigate the influence of different water managements on the growth of M. keisak under greenhouse conditions, and to assess the efficacy of common rice herbicides against it under field conditions.Three water management techniques were tested under greenhouse conditions: saturation, intermittent irrigation, and continuous flooding. The efficacy against M. keisak was evaluated in paddy fields during 2003–2005. In 2003, bispyribac-sodium was applied alone or in combination with triclopyr or metosulam at 20, 27, and 32 days after seeding (DAS). In 2004 and 2005, bispyribac-sodium was applied once (30 DAS), but at two application rates.Results for the three water treatments showed continuous flooding reduced M. keisak biomass most as confirmed by aboveground fresh weights. In the paddy field experiments, bispyribac-sodium also proved highly effective against M. keisak and was selective to rice with more than 90% efficacy. The addition of tryclopyr or metosulam to bispyribac-sodium failed to improve its herbicidal efficacy. Finally, the best M. keisak control at field condition was obtained with continuous flooding combined with bispyribac-sodium.     

Diclofop resistance in sterile wild oat (Avena sterilis L.) in wheat fields in Greece and its management by other post-emergence herbicides

In 2009, a survey was conducted of cereal fields in five prefectures of Greece to establish the frequency and distribution of herbicide-resistant sterile wild oat (Avena sterilis L.). In total, 104 sterile wild oat accessions were collected and screened in a field experiment (conducted in 2009 and repeated in 2010) with several herbicides commonly used to control this weed. Most of the sterile wild oat accessions (89%) were classed as resistant (or developing resistant) to the ACCase-inhibiting herbicide diclofop, while resistance to other ACCase-inhibiting herbicides was markedly lower. The results of the pot experiments showed that some of the sterile wild oat accessions were found to have a very high level of diclofop resistance (resistance index up to 28.6), while cross-resistance with other herbicides was common. The levels of resistance and cross-resistance patterns varied among biotypes with different amount and time of selection pressure, indicating either more than one mechanism of resistance or different resistance mutations in these sterile wild oat biotypes. LA14, which had the highest diclofop resistance level (28.6 resistance index), showed resistance to all APP herbicides applied and non-ACCase inhibitors. Alternative ACCase-inhibiting herbicides, namely tralkoxydim and pinoxaden remain effective on 86 and 92% of the tested sterile wild oat populations, respectively. For the ALS-inhibiting herbicide mesosulfuron + iodosulfuron, nearly all the sterile wild oat accessions were susceptible (97%), with only 3 of them classed as developing resistance. Therefore, there is an opportunity to effectively control sterile wild oat by selecting from a wide range of herbicides and other cultural practices. Early post-emergence herbicide application is strongly suggested, since it could decrease the number of resistant seeds in the field and slow down the dispersal of this major problem.     

Distribution and frequency of resistance to four herbicide modes of action in Lolium rigidum Gaud. accessions randomly collected in winter cereal fields in Spain

Lolium rigidum is the most prevalent and damaging grass weed of winter cereals in Spain. L. rigidum infestations are frequently treated with herbicides and, consequently, populations have evolved resistance. The objective of this study was to determine the extent and frequency of herbicide resistance in L. rigidum populations in Spain to the selective herbicides chlortoluron, diclofop-methyl and chlorsulfuron, commonly used for its control in-crop, and to glyphosate. The response to these herbicides was evaluated on 123 accessions surveyed randomly across cereal cropping areas of the regions of Castile and León, Catalonia and Andalusia. The fresh weight and the frequency of undamaged plants were calculated for each accession and herbicide. At the regional level, higher frequencies of accessions displaying resistance occurred in Catalonia, an intensively cropped region with a greater herbicide selection pressure. Of concern is that in this region the 60% of the accessions displayed some level of resistance to the ALS-inhibiting herbicide chlorsulfuron. The 6.9% of the accessions found in Castile and León with some resistance to glyphosate could also indicate an incipient problem of resistance to this herbicide. For the other herbicides and regions the majority of the accessions remained susceptible. The possible mechanisms of herbicide resistance development in L. rigidum accessions (target-site versus non-target-site resistance) and their variation among regions was discussed. This study can be used to generate herbicide resistance-management schemes for farmers, based upon the herbicide the site and the potential for resistance development.     

Polymorphisms in the ALS gene of weedy rice (Oryza sativa L.) accessions with differential tolerance to imazethapyr

Herbicide-resistant Clearfield™ rice technology allows the use of ALS inhibitors to control weedy rice. Weedy rice plants have differential tolerance to imazethapyr, perhaps due to ALS polymorphisms. We aimed to assess ALS polymorphisms in weedy rice accessions from Arkansas, USA, with differential tolerance to imazethapyr in seedling growth bioassays. Six base changes were identified in the ALS of 14 weedy rice accessions. Three of these nucleotide changes resulted in amino acid substitutions — Pro⁹³Thr, Glu⁶³⁰Asp, and Val⁶⁶⁹Met — in four accessions: Ark-4, Ark-9, Poi-1 and Poi-6. The GR₅₀ values and inhibition of root and shoot growth (%) of these accessions differed. The Glu⁶³⁰Asp substitution occurs in the herbicide binding domain B and Val⁶⁶⁹Met occurs at the C-terminal tail where the co-factor binds. Variability in weedy rice ALS exists, but polymorphism patterns did not relate to tolerance levels. The observed mutations presented the possibility that sustained selection pressure will eventually lead to selection of a herbicide-tolerant individual that will be the progenitor of a resistant population. Concomitantly, pollen-mediated gene flow from Clearfield™ rice to weedy rice will lead to the evolution of ALS-resistant weedy rice populations.     

Cyperus difformis evolves resistance to propanil

Cyperus difformis L. is one of the worst weeds of rice world-wide and has evolved resistance to acetolactate synthase (ALS)-inhibiting herbicides in rice fields of California. Propanil use was intensified to control the widespread resistant biotypes. Rice growers have recently experienced poor control, suggesting resistance to this photosystem II-inhibiting herbicide may have evolved in C. difformis populations. The objectives of this study were to detect the presence of propanil resistance, to establish resistance levels, and to investigate involvement of enhanced herbicide detoxification as mechanism of resistance through the use of metabolic inhibitors. Four C. difformis populations collected in rice fields from the Sacramento Valley of California were confirmed resistant to propanil. This is the first case of such resistance outside the Poaceae and the first time C. difformis exhibits resistance to an herbicide mechanism of action other than ALS inhibition. Carbaryl and malathion applied individually in mixture with propanil had minor effects on herbicide toxicity suggesting metabolic detoxification was not a resistance mechanism. A resistant biotype produced more than 80% biomass after a propanil (6.7 kg a.i. ha⁻¹) and carbaryl (1.9 kg a.i. ha⁻¹) or propanil and malathion (1.0 kg a.i. ha⁻¹) treatment compared to <20% by a susceptible biotype, suggesting substantial resistance still persisted in spite of insecticide addition. Propanil-resistant plants were cross-resistant to bensulfuron-methyl, imazosulfuron, halosulfuron-methyl and penoxsulam, but susceptible to carfentrazone. The loss of propanil to control this important weed of rice underscores the fragility of herbicide-based weed control in monoculture rice. Integrated weed management approaches to decrease herbicide selection pressure are needed to mitigate the evolution of multiple-herbicide resistance in C. difformis of California rice.     

Characterisation and management of Phalaris paradoxa resistant to ACCase-inhibitors

Phalaris paradoxa is a competitive grass commonly found in durum wheat crops of central and southern Italy. Among the 85 populations screened from 1998 to 2008 for resistance to ACCase-inhibitors and graminicide sulfonylureas, 17 resulted as being resistant to at least one ACCase inhibitor while none of the populations showed resistance to sulfonylureas. ACCase resistance in hood canary-grass seems to be spreading rather slowly in Italy. Out of the 17 populations, seven were characterised through outdoor dose-response pot experiments to investigate resistance levels and cross-resistance patterns to ACCase-inhibitors and multiple resistance to other mode of action. Molecular bases of resistance to the recently introduced DEN herbicide pinoxaden were also investigated. Six populations were confirmed to be ACCase-resistant with various cross-resistance patterns. Two populations were resistant to all tested ACCase herbicides, with pinoxaden resistance indexes (RI) based on survival ranging from 22 to 50. The two populations have been molecularly characterised for resistance to pinoxaden. A single point-mutation in the ACCase gene was identified in each population, causing the amino-acid substitutions of Ile₁₇₈₁Val and Asp₂₀₇₈Gly in 0478L and 0025, respectively. The results suggest that resistance of P. paradoxa to pinoxaden is due to an altered target site and different mutations cause different resistance levels. The biological characteristics of the species, mainly self-pollinated, and the absence of multiple resistance allow herbicides with different modes of action to be used for controlling ACCase-resistant populations. Chemical tools should be carefully used within integrated weed management strategies.     

Genetic inheritance of cytochrome P450-mediated metabolic resistance to chlorsulfuron in a multiple herbicide resistant Lolium rigidum population

Field evolved resistance to acetolactate synthase (ALS)-inhibiting herbicides in a multiple resistant Lolium rigidum population (VLR69) is known to be mainly due to enhanced rates of herbicide metabolism, likely involving cytochrome P450 monooxygenases. The present study investigates genetic inheritance of P450-mediated metabolic resistance to the ALS-inhibiting herbicide chlorsulfuron. To this end, a P450-mediated, metabolism-based resistant sub-set of VLR69 was carefully selected using plant vegetative cloning, appropriate herbicide screen test and the known P450 inhibitor malathion. Both intermediate and near-dominant nuclear-encoded phenotypic resistance traits were observed in 14 reciprocal F₁ families. The segregation of phenotypic chlorsulfuron resistance in ψ-F₂ families was analysed using genetic inheritance models involving one or two loci. The results from four ψ-F₂ families revealed complex patterns of genetic inheritance of P450-mediated metabolic resistance in genetically diverse and cross-pollinated species L. rigidum: multiple loci are likely involved and interact with herbicide rates and environmental conditions in mediating the resistance phenotype.     

Regional scale distribution of imidazolinone herbicide-resistant alleles in red rice (Oryza sativa L.) determined through SNP markers

Red rice is the main weed in rice paddy fields. Imidazolinone herbicides in resistant rice cultivars currently provide a unique opportunity to control red rice in large-scale rice fields. However, the continuous use of this technology has resulted in imidazolinone-resistant red rice biotypes. This study aimed to identify the mechanism of herbicide resistance and the frequency and spatial distribution of the known imidazolinone herbicide-resistant alleles in red rice. The nucleotide sequence of the ALS gene indicated that the G₆₅₄E, S₆₅₃D and A₁₂₂T mutations are present in the imidazolinone herbicide-resistant rice cultivars IRGA 422 CL, SATOR CL and PUITÁ INTA CL, respectively. This information and the nucleotide sequence surrounding these mutations were used for the development of single nucleotide polymorphism (SNP) molecular markers to identify the possible mutations that confer herbicide resistance in red rice. This analysis was carried out in a total of 481 plants from 38 populations collected as individuals that escaped control with the herbicides imazethapyr and imazapic in rice paddy fields in Southern Brazil. The G₆₅₄E mutation was the most frequent, being found in 100% and 90.9% of the populations in the 2006/2007 and 20007/2008 seasons, respectively. In addition, the S₆₅₃D and A₁₂₂T mutations were also present either alone or as double or triple mutations in some plants. Target site insensitivity is the predominant mechanism of resistance in red rice resistant to imidazolinone herbicides in Southern Brazil. The high frequency of the S₆₅₃D mutation, the same mutation responsible for the resistance in the rice cultivar largely used in Southern Brazil, indicates that gene flow is occurring from the rice cultivar to red rice. Management practices related to increasing crop sanitation and decreasing of herbicide selection pressure through crop rotation should be enforced to prevent the evolution of herbicide resistance in red rice.     

Evaluation of the management practice for controlling herbicide runoff from paddy fields using intermittent and spillover-irrigation schemes

Two water management practices, an intermittent irrigation scheme using automatic irrigation system (AI) and a spillover-irrigation scheme (SI), were compared for the fate and transport of commonly used herbicides, mefenacet (MF) and bensulfuron-methyl (BSM) in experimental paddy plots. Maximum mefenacet concentrations in paddy water were 660 and 540 μg L⁻¹ for AI and SI plot, respectively. The corresponding values for bensulfuron-methyl were 46.0 and 42.0 μg L⁻¹. Dissipation of the herbicides in paddy water appeared to follow the first-order kinetics with half-lives (DT₅₀) of 1.9–4.5 days and DT₉₀ (90% mass dissipation) of 7.8–11.3 days. The AI plot had no surface drainage, hence no herbicide was lost through paddy-water discharge. However, SI plot lost about 38 and 49% of applied mefenacet and bensulfuron-methyl, respectively. The intermittent irrigation scheme using automatic irrigation system with a high drainage gate was recommended to be a best management practice for controlling the herbicide losses from paddy fields. The paddy field managed by spillover-irrigation scheme may cause significant water and herbicide losses depending on the volume of irrigation and precipitation. The water holding period after herbicide application was suggested to be at least 10 days according to the DT₉₀ index.     

Biology,impact, and management of Echinochloa colona (L.) Link

Echinochloa colona (L.) Link. is one of the most problematic weeds across the world. It is an annual C₄ summer grass, native to tropical and subtropical Asia, emerged as a serious and persistent threat in 35 cropping systems in more than 60 countries. E. colona is reported as an important associated weed species in transplanted and direct-seeded rice. Diverse ecotypes, high seed production, short seed dormancy, rapid growth, competitive potential, allelopathic interaction, and resistance against several herbicides makes it a more adaptable and persistent challenge in various agro-ecosystems. Development of resistance to recommended or higher doses of numerous herbicides, including ametryn, atrazine, bispyribac-sodium, clefoxidym, cyhalofop-butyl, fenoxaprop-p-ethyl, glyphosate, metribuzin, propanil, and triazine, is a serious concern for the farming and scientific community. Crop infestation with resistant E. colona biotypes may ultimately increase the weed control cost. Unfortunately, investigations on seed dormancy release, genetic diversity, allelopathic interference, and competitive ability of this weed are inadequate in accomplishing its appropriate control in different environments. Therefore, a comprehensive review is presented here to gather the existing information, to pin point key findings, and to highlight the research gaps in the biology, interference, and management of E. colona. Different management options have been discussed in relation with eco-biology of this noxious weed. The potential research endeavours have also been highlighted in order to provide an insight of its existing scenario and to facilitate the future management strategies.     

Control of volunteer cereals with post-emergence herbicides in maize (Zea mays L.)

Volunteer winter cereals are found sporadically in maize (Zea mays L.) fields across southern Ontario. Seven field trials were conducted over a two-year period (2006 and 2007) at four locations to determine the efficacy of five acetolactate synthase (ALS)-inhibiting herbicides for the control of volunteer cereals applied at two post-emergence application timings (2–4 and 4–7 maize leaf tips). The volunteer cereals were a hard red winter wheat (Triticum aestivum L.) (‘Hyland AC Morley’), soft red winter wheat (‘Pioneer 25R47’), soft white winter wheat (‘Pioneer 25W41’), and a autumn rye (Secale cereale L.) (‘FR’) cultivar. Volunteer cereal competition in maize resulted in a yield reduction of up to 44%. Foramsulfuron, nicosulfuron, nicosulfuron/rimsulfuron provided greater than 70% control of the volunteer cereals at 56 days after treatment (DAT), while primisulfuron and rimsulfuron provided greater than 60% control. Volunteer cereal control with early and late application was greater than 82 and 61%, respectively. Hard red winter wheat was the most sensitive to the ALS-inhibiting herbicides with control of 84–93%. Soft red and soft white winter wheat cultivars were intermediate in sensitivity with control of 76–87%, while autumn rye was the least sensitive with control of at 56–71% control at 56 DAT. Maize yields were improved when volunteer cereals were controlled with the use of herbicides compared to the weedy control, but were lower than the weed-free control. Early herbicide application resulted in improved control of volunteer cereals and higher maize yield.     

Improved metribuzin tolerance in narrow-leafed lupin (Lupinus angustifolius L.) by induced mutation and field selection

Narrow-leafed lupin (Lupinus angustifolius L.) is a grain legume well adapted to sandy soils of a Mediterranean climate and is the major grain legume in Australia. Improved herbicide tolerance of lupin cultivars is now considered as top priority by the industry for effective weed management. This paper reports induced mutation by seed mutagenesis in metribuzin-sensitive but anthracnose resistant cv. Tanjil, selection for metribuzin tolerant mutants in the field and evaluation of the tolerant mutants to metribuzin and anthracnose resistance. Two highly tolerant mutants Tanjil-AZ-33 and Tanjil-AZ-55 were identified and they were the first reported metribuzin tolerant mutants. The estimated mutation rate was 2.5 × 10⁻⁵. Tanjil-AZ-33 was six times and Tanjil-AZ-55 was four times more tolerant to metribuzin than the original cultivar Tanjil and they were also more tolerant than the tolerant cv. Mandelup. Tanjil-AZ-33 was the most tolerant lupin germplasm. Disease nursery assessment over 2 years revealed that both mutants also retained anthracnose resistance. Seed yield under irrigation was 4.2 t/ha for Tanjil-AZ-33 and 1.9 t/ha for cv. Tanjil when the seedlings were treated with metribuzin at 300 g/ha at the six-leaf stage. Clearly the mutation process has created new tolerance to metribuzin, but did not alter the anthracnose resistance. The mutant Tanjil-AZ-33 has been used as a parent in the lupin breeding program as a source of both metribuzin tolerance and anthracnose resistance. Seed mutagenesis followed by field selection in M₂ proved to be an effective method to develop new tolerance to herbicides.     

Application timing and adjuvant type affected saflufenacil efficacy on selected broadleaf weeds

Saflufenacil is a new herbicide being developed for pre-plant burndown and pre-emergence broadleaf weed control in field crops, including maize, soybean, sorghum and wheat. Field experiments were conducted in 2007 and 2008 in northeast Nebraska, USA to describe dose-response curves of saflufenacil applied in mid (early post-emergence, EPOST) and late May (late post-emergence, LPOST) with several adjuvants for spring emerging broadleaf weed control. Dose-response curves based on log-logistic model were utilized to determine the ED₉₀ values (effective dose that provides 90% weed control efficacy) for Convolvulus arvensis, Lactuca serriola, Lamium amplexicaule, Capsella bursa-pastoris, Taraxacum officinale, Thlaspi arvense and Conyza canadensis. In general, weed control efficacy was influenced by application timing and type of adjuvant. EPOST application of saflufenacil resulted better efficacy of saflufenacil compared to LPOST. Addition of spray adjuvants improved efficacy of saflufenacil. For example, 90% control of T. arvense was obtained at EPOST application with 251, 161, 96 and 59 g a.i. ha⁻¹ for saflufenacil applied alone, or tank-mixed with NIS (nonionic surfactant), COC (crop oil concentrate), or MSO (methylated seed oil), respectively. In contrast, the ED₉₀ values with LPOST application were 333, 201, 127 and 79 g a.i. ha⁻¹ for saflufenacil applied alone, or with NIS, COC and MSO, respectively. MSO was the best adjuvant, which provided the most enhancement of saflufenacil. COC was the second best, or similar to MSO, on many weed species. NIS provided the least enhancement of saflufenacil. The ED₉₀ values determined for different broadleaf weed species are within the proposed label dose of saflufenacil.     

山东省小麦田看麦娘对甲基二磺隆的抗性及其基因突变

为明确山东省麦田看麦娘种群对甲基二磺隆的抗性情况及可能存在的抗性机理,本研究在临沂、日照等山东省看麦娘发生严重地区的小麦田共采集10个看麦娘种群,在温室条件下测定了其对甲基二磺隆的抗性以及对其他4种除草剂的敏感性,扩增和比对了靶标酶乙酰乳酸合成酶(acetolactate synthase,ALS)基因部分片段的差异。结果表明,SDTC-4种群对甲基二磺隆具有高抗性,抗性倍数达30.1,其他种群对甲基二磺隆敏感,抗性倍数在1.0~1.8之间。对ALS基因片段测序发现,SDTC-4种群看麦娘ALS基因197位氨基酸由脯氨酸(CCC)突变为丝氨酸(TCC)(P197S),其他种群均未发现有突变产生。SDTC-4种群对啶磺草胺和氟唑磺隆产生了一定的交互抗性,在推荐剂量下死亡率分别为10.0%和13.3%。所有的看麦娘种群对精噁唑禾草灵和异丙隆敏感,推荐剂量下死亡率达100%。本研究是看麦娘对甲基二磺隆抗性在山东省的第一例报道,ALS基因P197S突变是第一次在看麦娘中被发现,该突变很可能是导致SDTC-4种群对甲基二磺隆产生抗性的重要原因之一。     

Integrated effect of allelochemicals and herbicides on weed suppression and soil microbial activity in wheat (Triticum aestivum L.)

To evaluate the allelopathic effects of major crops and weeds, studies were conducted during 2011–12 and 2012–13 by utilizing water extracts of allelopathic plants namely rice (Oryza sativa L.), Parthenium hysterophorus L., Phragmites australis Cav., and Datura alba L. with reduced rates of fenoxaprop-p-ethyl and bromoxynil plus MCPA to control weeds. Application of Phragmites australis and Parthenium hysterophorus along with lower rates of fenoxaprop-p-ethyl and bromoxynil plus MCPA showed promising results by controlling weeds and improving yield. Parthenium hysterophorus extract with half of the recommended dose of fenoxaprop-p-ethyl and bromoxynil plus MCPA reduced weed density by 51 and 50% during year 1 and year 2, respectively, compared with the control. Phragmites australis extract with half of the recommended dose of fenoxaprop-p-ethyl produced grain yield (5.7 and 6.1 t ha⁻¹ during year 1 and 2, respectively) in wheat. However, these results were also at par with Parthenium hysterophorus and Datura alba extracts in combinations with half the recommended doses of the above mentioned herbicides. The study of microbial activity showed higher amount of mineralizable carbon in D. alba with half the recommended dose of fenoxaprop-p-ethyl treated plots (0.073 g during both the years). The lowest amount of mineralizable carbon (0.035 and 0.030 g during year 1 and 2, respectively) was observed in the control plots. The presence of allelopathic plants in field crops and subsequent mixing in soil by tillage may create problems in crop production. Therefore, further studies are suggested to fully explore all the possible interactions among allelochemicals and herbicides.     

Efficiency of mesosulfuron-methyl and clodinafop-propargyl dose for the control of Lolium perenne in wheat

Increasing environmental and economic concerns have resulted in considering the potential for the successful use of herbicides at lower doses within an integrated approach to weed management. Therefore, field experiments were carried out to evaluate the efficiency of mesosulfuron-methyl and clodinafop-propargyl dose to control Lolium perenne in pure stand and in mixture with wheat. The herbicides at 5 different doses were assigned in a factorial arrangement (subplots) within planting systems (mainplots). L. perenne biomass was totally different in pure stand and in mixed planting system, irrespective of the herbicide effect. More than 3-fold decrease was caused in the L. perenne biomass by the presence of wheat. Mesosulfuron-methyl was more potent than clodinafop-propargyl in the L. perenne control. Mixed planting enhanced the herbicide performance, increasing the relative potency value of mesosulfuron-methyl. The wheat grain yield received no additional benefit from applying mesosulfuron-methyl at the full recommended dose rather than at half dose. This study demonstrates that L. perenne suppression involving sub-lethal herbicide dose is associated with the wheat competitiveness. Combining competitive cropping systems with reduced herbicide could be an approach to reducing weed populations over time with lower crop production costs.     

我国抗ALS类除草剂油菜种质创制与研究进展

化学除草是控制田间草害的有效手段,但我国油菜化除面积非常有限。创制对特定除草剂具有选择抗性的油菜新种质,选育抗性品种是实现我国油菜化除的有效途径。乙酰乳酸合酶(acetolactate synthase,ALS) 类除草剂具有高效低量、选择性强、杀草谱广等优点,在生产上得到广泛应用。本文简述了ALS 基因及其突变产生抗性的机制,着重介绍我国基于ALS靶酶突变的抗除草剂油菜种质创制、抗性生理生化和分子机理等方面的研究进展,并探讨了抗除草剂新种质在油菜抗性新品种选育、杂交油菜制种及抗性基因在转基因工程中的应用。     

Integration of soil-applied herbicides at the reduced rates with physical control for weed management in fennel (Foeniculum vulgare Mill.)

Fennel has been widely used in traditional medicine for their antimicrobial effects. Since fennel is long duration crop and have slow initial growth, it protection from weed is essential. Experiments were conducted for two consecutive seasons to evaluate the efficacy of soil-applied herbicides at the reduced rates in combination with physical control for weed management and optimizing the yield of fennel. Treatments were type of herbicide (trifluralin and pendimethalin), application dose (recommend dose (R), 75% R, 50% R, and 0% R) and physical weed control (none, one hand-weeding at 50 day after planting (DAP), wheat straw mulch). Weed-free control treatment was also included in each year. The results showed that the use of soil-applied herbicides resulted in reduced weed biomass but did not provide season long weed control without an additional physical control. In both seasons, pendimethalin provided better weeds control than trifluralin. Reduced herbicide rates were found to be more effective when herbicides application followed by hand-weeding than when were used alone or combined with mulch. Experimental results also showed that one time increasing in herbicide rates increased seed yield by 17.5 and 7.5% in 2012 and 16.5 and 6.3% in 2013, when one hand-weeding and mulching were used as supplemental control, respectively. Overall, the 75% of the labeled recommended rate of herbicides followed by one hand-weeding at 50 DAP produced consistently high yields and less weed biomass, reflecting both superior weed control and crop safety.     

Susceptibility variation to new and established herbicides: Examples of inter-population sensitivity of grass weeds

The objectives of this study were to describe the intra-specific variation in herbicide response of weed populations when subjected to new vs. well-established herbicides, and to assess distributions of logLD₅₀- and logGR₅₀-estimates as a potential indicator for early resistance detection. Seeds of two grass weeds (Alopecurus myosuroides, Apera spica-venti) were collected in southern Sweden, mainly in 2002. In line with the objectives of the study, the collections sites were not chosen for noted herbicide failures nor for detected herbicide resistance, but solely for the presence of the target species. For each species, seedlings were subjected to two herbicides in dose-response experiments in a greenhouse. One herbicide per species was recently introduced and the other had been on the market for control of the species for a decade, with several reports of resistance in the literature. Fresh weight of plants and a visual vigour score were used to estimate GR₅₀ and LD₅₀, respectively. Resistance to fenoxaprop-P-ethyl in A. myosuroides was indicated by the LD₅₀-estimates to be present in frequencies sufficient to affect the population-level response in 9 of 29 samples, and was correlated to response to flupyrsulfuron, while low susceptibility to isoproturon in A. spica-venti populations was not linked to the response to sulfosulfuron. In the study as a whole, the magnitude of the estimated herbicide susceptibility ranges differed irrespective of previous exposure. No consistent differences were found in the distribution of LD₅₀-estimates for new and “old” herbicides, and normality in the distribution of estimates could not be assumed for a non-exposed sample, even in the absence of an indication of cross-resistance.     

Fitness costs associated with 1781 and 2041 ACCase-mutant alleles conferring resistance to herbicides in Hordeum glaucum Steud.

The amino acid substitutions that confer herbicide resistance may also involve fitness costs leaving mutant plants at a competitive disadvantage compared with wildtypes. This research investigated the effect of two target–site point mutations of ACCase gene: Ile-1781-Leu/Val and Ile-2041-Asn on plant growth and fecundity of Hordeum glaucum biotypes grown in monoculture and/or under interspecific competition in the field with Triticum aestivum L. and Lens culinaris M. The amino acid substitutions at 1781 position of ACCase gene did not impose any negative pleiotropic effects on relative growth rate (RGR), panicle emergence, plant height, total biomass, and seed production in H. glaucum mutant plants. There was some evidence for fitness cost associated with Ile-2041-Asn mutation in terms of reduced RGR and reduced vegetative biomass and seed production when grown in competition with L. culinaris. The absence of measurable negative pleiotropic effects on plant growth and fecundity associated with Ile-1781-Leu/Val ACCase mutations in H. glaucum suggest that the frequency of these alleles will not decline in the absence of herbicide selection pressure. However, the 2041-Asn allele could decrease in frequency in the absence of herbicide selection pressure.