Physiological and biochemical mechanisms behind the fast action of glufosinate

2019 Fall.Includes bibliographical references.Glufosinate is one of the few herbicides that are still effective for controlling herbicide resistant weeds, but its performance is often inconsistent and affected by environmental conditions. It inhibits glutamine synthetase (GS) by competing with glutamate for the active binding site. Unlike other amino acid biosynthesis inhibitors, glufosinate is a fast-acting herbicide and susceptible plants develop visual symptoms within a few hours after treatment. Inhibition of GS leads to ammonia accumulation and photosynthesis inhibition, which have traditionally been proposed as the causes of the rapid phytotoxicity. This dissertation presents a new understanding of the mechanism(s) of action of glufosinate and a biochemical approach to improve its herbicidal efficacy. Glufosinate uptake is inhibited by glutamine levels in the plant, and translocation is not affected by the rapid phytotoxicity. Glufosinate translocates primarily through the apoplast (xylem) rather than the symplast (phloem) probably due to its physicochemical properties and the absence of an effective membrane transporter. Glufosinate efficacy is proportional to the herbicide concentration in leaf tissues. Neither ammonia accumulation nor carbon assimilation inhibition are directly associated with the fast action of glufosinate. Instead, rapid phytotoxicity results from a massive light-dependent accumulation of reactive oxygen species (ROS). Inhibition of GS blocks the photorespiration pathway leading to a massive photooxidation damage. Under full sunlight, the excess of electrons is accepted by molecular oxygen leading to ROS generation. These free radicals cause lipid peroxidation, which ultimately leads to rapid cell death. The addition of protoporphyrinogen oxidase (PPO) inhibitors to glufosinate enhances ROS accumulation and herbicidal activity. This enhanced activity results from protoporphyrin formation at high levels due to a transient accumulation of glutamate, the precursor for chlorophyll biosynthesis. The herbicide combination also showed enhanced activity in the field and may help to overcome the lack of glufosinate efficacy under certain environmental conditions

ACCase-inhibiting herbicides: mechanism of action, resistance evolution and stewardship

Herbicides play an important role in preventing crop yield losses due to both their weed interference ability and their capacity for increasing soil conservation in no-till systems. Group A herbicides or acetyl-CoA carboxylase (ACCase) are essential tools the selective management of glyphosate resistance in grass weed species. In this review, we describe important aspects of ACCase biology and herbicides targeting this enzyme, along with a discussion on stewardship programs to delay the evolution of herbicide resistance which can evolve either through target site and/or non-target site mechanisms. Sixteen-point mutations have been reported to confer resistance to ACCase inhibitors. Each mutation confers cross resistance to a different group of herbicides. Metabolic resistance can result in resistance to multiple herbicides with different mechanisms of action (MoA), and herbicide detoxification is often conferred by cytochrome P450 monooxigenases and glutathione-Stransferases. Regardless of whether resistance mechanisms are target or non-target site, using herbicides with the same MoA will result in resistance evolution. Therefore, while field surveys and resistance mechanism studies are crucial for designing reactive management strategies, integrated weed management plays a central role in both reactive and proactive mitigation of herbicide resistance evolution

Dry season and soil texture affect the chemical control of monocotyledonous in sugarcane

The chemical weed control in sugarcane during the wet season is more effective than the control carried out during the dry season. The objective of this study was to evaluate the efficacy of herbicides in the rainy season and in the dry season in sugarcane crop, and in different soil textural classes. The experiments simulated dry season and rainy season basing on periods of days in which experiment was submitted to irrigation restriction. In each experiment, it was tested 50 and 100% of the dose of the main herbicides commonly used in sugarcane to control B. decumbens, B. plantaginea, P. maximum and D. horizontalis. In general, in dry conditions, as well as varying the soil texture, there are restrictions in the choice of herbicide to be used due to the reduced effectiveness of some treatments in certain situations. In the very-clayey soil, especially in the dry season, the efficacy of herbicides is better, whereas, for the sandy-clay-loam soil in dry conditions, the effectiveness of herbicides is restricted. Thus, this study, despite the great complexity of the variables to be analyzed, permitted to establish guidelines for decision making on the most appropriate herbicide to be applied in each studied condition, in order to control these weed species.The chemical weed control in sugarcane during the wet season is more effective than the control carried out during the dry season. The objective of this study was to evaluate the efficacy of herbicides in the rainy season and in the dry season in sugarcane crop, and in different soil textural classes. The experiments simulated dry season and rainy season basing on periods of days in which experiment was submitted to irrigation restriction. In each experiment, it was tested 50 and 100% of the dose of the main herbicides commonly used in sugarcane to control B. decumbens, B. plantaginea, P. maximum and D. horizontalis. In general, in dry conditions, as well as varying the soil texture, there are restrictions in the choice of herbicide to be used due to the reduced effectiveness of some treatments in certain situations. In the very-clayey soil, especially in the dry season, the efficacy of herbicides is better, whereas, for the sandy-clay-loam soil in dry conditions, the effectiveness of herbicides is restricted. Thus, this study, despite the great complexity of the variables to be analyzed, permitted to establish guidelines for decision making on the most appropriate herbicide to be applied in each studied condition, in order to control these weed species

Development And Grain Quality Of Soybean Cultivars Treated With Pyraclostrobin And Biostimulant

Products with physiological effects on plants to optimize agricultural production is increasingly used; they can change the development of plants and the chemical characteristics of seeds. The objective of this work was to evaluate the development of soybean cultivars and the protein and oil contents of soybean grains after treatment with pyraclostrobin and biostimulant. The experiment was carried out with soybean crops without irrigation. The experimental design was a randomized complete block design, with five replications, using a 3 × 3 factorial arrangement consisting of three cultivars of different maturation times (very early, M6952IPRO; early M7739IPRO; and medium, ST797IPRO), and three treatments with products that cause physiological effects (control, pyraclostrobin, and control + biostimulant). The pod, leaf, and stem dry weights, number of pods, 100-grain weight, grain yield, and oil and protein contents of the soybean plants were evaluated. The data were subjected to analysis of variance, and Tukey’s test at 5% probability. The effects of the products used (pyraclostrobin and biostimulant) vary according to the cultivar and may increase the soybean leaf and pod dry weights, and grain protein contents.Products with physiological effects on plants to optimize agricultural production is increasingly used; they can change the development of plants and the chemical characteristics of seeds. The objective of this work was to evaluate the development of soybean cultivars and the protein and oil contents of soybean grains after treatment with pyraclostrobin and biostimulant. The experiment was carried out with soybean crops without irrigation. The experimental design was a randomized complete block design, with five replications, using a 3 × 3 factorial arrangement consisting of three cultivars of different maturation times (very early, M6952IPRO; early M7739IPRO; and medium, ST797IPRO), and three treatments with products that cause physiological effects (control, pyraclostrobin, and control + biostimulant). The pod, leaf, and stem dry weights, number of pods, 100-grain weight, grain yield, and oil and protein contents of the soybean plants were evaluated. The data were subjected to analysis of variance, and Tukey’s test at 5% probability. The effects of the products used (pyraclostrobin and biostimulant) vary according to the cultivar and may increase the soybean leaf and pod dry weights, and grain protein contents

Dry season and soil texture affect the chemical control of Senna obtusifolia in sugarcane

Devido às suas características intrínsecas, o fedegoso (Senna obtusifolia) tem ganhado importância em canaviais, principalmente onde há predomínio de palhada após a colheita mecânica. O objetivo deste trabalho foi avaliar a eficácia de herbicidas pré-emergentes utilizados na cultura da cana-de-açúcar no controle de fedegoso em solos de diferentes texturas e épocas de aplicação. Foram realizados dois experimentos para cada época de aplicação (seca e úmida), sendo um para cada classe textural de solo (muito-argiloso e franco-argilo-arenoso), totalizando quatro experimentos. Os tratamentos foram constituídos por 17 herbicidas na época úmida e 11 herbicidas na época seca (todos os herbicidas foram aplicados em 50 e 100% da dose recomendada), além da testemunha sem aplicação para cada época e solo, sendo o delineamento inteiramente ao acaso. O tipo de solo e a época de aplicação alteraram a eficiência dos herbicidas. Para a época úmida, inicialmente, todos os herbicidas, exceto trifluralin e s-metolachlor, resultaram em controle satisfatório de fedegoso. Tebuthiuron foi o herbicida que proporcionou maior período residual de controle. Para a época seca, amicarbazone, flumioxazin, hexazinone, imazapic, [diuron + hexazinone] F1 e isoxaflutole foram eficazes em ambos os solos, mas somente em avaliações iniciais; [diuron + hexazinone] F1 e amicarbazone foram os herbicidas que proporcionaram maior período residual de controle. Because of its intrinsic characteristics, sicklepod (Senna obtusifolia) has gained importance in sugarcane, especially where there is a predominance of straw after mechanical harvest. The objective of this study was to evaluate the efficacy of preemergence herbicides used in sugarcane to control sicklepod in different soil textures and application timings. Two experiments were carried out for each application season (dry and wet), and one experiment for each soil textural class (clay and sandy clay loam), totaling four experiments. The treatments consisted in 17 herbicides in the wet season and 11 herbicides in the dry season (all herbicides were applied at 50 and 100% of the recommended dose) and a check without application for each season and soil, and the design was completely randomized. Soil texture and application timing have altered the herbicide efficacy. For the wet season, initially, all herbicides, except trifluralin and s-metolachlor, resulted in satisfactory control of sicklepod. Tebuthiuron was the herbicide that provided the longest period of residual control. For the dry season, amicarbazone, flumioxazin, hexazinone, imazapic, [diuron + hexazinone] F1 and isoxaflutole were efficient in both soils, but only in initial evaluations; [diuron + hexazinone] F1 and amicarbazone were the herbicides that provided the longest period of residual control.

Curvas de dose-resposta e eficácia de herbicidas inibidores da enzima ALS aplicados em pré-emergência sobre espécies de Amaranthus

Weeds from Amaranthus genus may cause major yield losses in economic crops, including cotton, if not controlled properly. In order to avoid it, it’s necessary correct species identification, besides herbicides suitability and recommended doses. The aim of this study was to develop the dose-response curve of ALS enzyme inhibitors herbicides (trifloxysulfuron-sodium and pyrithiobac-sodium) applied in pre emergence conditions becoming possible to verify the control effectiveness over four important species of Amaranthus (A. hybridus, A. viridis, A. lividus and A. deflexus) as well as the difference in susceptibility between them. For each herbicide, isolated experiments were carried out and studied doses were: 0; 1.8; 3.7; 7.5; 15.0 and 30.0 for trifloxysulfuron-sodium and 0; 35; 70; 140; 280 e 560 for pyrithiobac-sodium, equivalent to 0, ¼, ½, 1, 2 and 4 times recommended rate for clay loam soils. Results indicated that used doses to obtain dose-response curve of trifloxysulfuron-sodium and pyrithiobac-sodium provided control higher than 80% for all Amaranthus species, characterizing the possibility of herbicides application in pre emergence conditions. Besides it, differential susceptibility between Amaranthus species were reported, being A. hybridus and A. lividus the most susceptible species to both herbicides.Plantas daninhas do gênero Amaranthus podem causar grandes perdas de produtividade nas culturas de interesse econômico se não controladas corretamente, entre elas do algodoeiro. Para que isso não aconteça é necessário a correta identificação das espécies, além da adequação de herbicidas e doses a serem utilizadas. Assim, o objetivo deste trabalho foi desenvolver as curvas de dose-resposta de herbicidas inibidores da enzima ALS (trifloxysulfuron-sodium e pyrithiobac-sodium) aplicados em pré-emergência, afim de verificar a eficácia de controle sobre espécies de Amaranthus (A. hybridus, A. viridis, A. lividus e A. deflexus) e a diferença de suscetibilidade entre elas. Para cada herbicida foram conduzidos experimentos isolados, onde as doses utilizadas em g ha-1 foram: 0,0; 1,8; 3,7; 7,5; 15,0 e 30,0 para trifloxysulfuron-sodium e 0; 35; 70; 140; 280 e 560 para pyrithiobac-sodium, equivalentes a 0, ¼, ½, 1, 2 e 4 vezes a dose comercial recomendada para solos de textura franco-argilosa. Os resultados indicaram que as doses utilizadas nas curvas de dose-respostas de trifloxysulfuron-sodium e pyrithiobac-sodium proporcionaram controles acima de 80% para todas as espécies de Amaranthus, caracterizando a possibilidade de utilização dos herbicidas em aplicações em pré-emergência. Houve diferença de suscetibilidade entre as espécies de Amaranthus, sendo A. hybridus e A. lividus as mais suscetíveis a ambos herbicidas

Alternativas para o controle químico de plantas voluntárias de crotalária em diferentes modalidades de aplicação

With the insertion of showy crotalaria as an antagonistic plant in areas with nematodes infestation history, the occurrence of volunteer plants from this species became common, making it necessary to adopt measures for their management. Thus, this work had the goal to evaluate the effectiveness of herbicides used on different species that where grown in rotation with showy crotalaria (C. spectabilis), aiming at its use in controlling volunteer plants from this species. Two experiments (herbicides applied in pre and post-emergence) were conducted on the field using the randomized block design, in (8x2)+1 factor scheme, with four replications. The variable evaluated in the experiments was the control percentage in different periods after treatment application; a plant stand was performed in the experiment with herbicides applied in pre-emergence. Atrazine and diuron, applied in pre-emergence, were the best treatments to control showy crotalaria volunteer plants; they did not suffer any influence from the applied dose. In addition to these, flumioxazin and fomesafen (60 and 375 g ha-1, respectively) were also good alternatives to control showy crotalaria in this application modality. For pre-emergent herbicides, with the exception of diuron (1500 g ha-1), all the other treatments were effective in controlling showy crotalaria in applications performed on plants with 2 to 4 leaves. As for the second application stage, 6 to 8 leaves, in addition to diuron (both doses), fomesafen applied in a lower dose (187.5 g ha-1), was not effective in controlling showy crotalaria, either.Com a inserção da crotalária como planta antagonista em áreas com histórico de infestação de fitonematoides, a ocorrência de plantas voluntárias desta espécie passou a ser comum, tornando-se necessária a adoção de medidas para o seu manejo. Assim, o presente trabalho teve por objetivo avaliar alternativas herbicidas aplicadas em diferentes modalidades (pré e pós-emergência) que possam ser utilizadas no controle de crotalária (Crotalaria spectabilis). Dois experimentos (herbicidas aplicados em pré e pós-emergência) foram conduzidos em campo adotando-se delineamento blocos ao acaso, em arranjo fatorial (8x2)+1, com quatro repetições. A variável avaliada nos experimentos foi porcentagem de controle em diferentes períodos após a aplicação dos tratamentos, sendo realizado estande de plantas no experimento com herbicidas aplicados em pré-emergência. Atrazine e diuron, aplicados em pré-emergência, consistiram nos melhores tratamentos visando ao controle de plantas voluntárias de crotalária, não sofrendo influência da dose aplicada. Além destes, flumioxazin e fomesafen (60 e 375 g ha-1, respectivamente) também consistiram em boas alternativas para o controle de crotalária nesta modalidade de aplicação. Para os herbicidas pós-emergentes, excluindo o diuron (1500 g ha-1), todos os demais tratamentos apresentaram eficácia no controle de crotalária em aplicações realizadas em plantas com 2 a 4 folhas. Para o segundo estádio de aplicação, 6 a 8 folhas, além do diuron (ambas as doses), o fomesafen aplicado na menor dose (187,5 g ha-1), também não apresentou eficácia no controle de crotalária

Herbicidas alternativos no controle de Bidens pilosa e Euphorbia heterophylla resistentes a inibidores de ALS na cultura do algodão

The presence of Bidens pilosa and Euphorbia heterophylla resistant to ALS inhibitors is a problem to weed management in cotton crop, due to the fact that few alternatives broadleaf selective herbicides area available. In order to supply this information gap, four experiments were established in greenhouse conditions with the objective of evaluating herbicides applied in post-emergence conditions, recommended either for conventional and transgenic cotton (resistant to glyphosate and amonio-glufosinate) for controlling these resistant biotypes. The experimental design was entirely randomized with four replications and 21 herbicides treatments, besides a check without herbicide application. Two experiments were conducted per species, where the first one corresponded to herbicides application in stages of two to four leaves, and the second in the stage of four to six. It was evaluated the percentage of control at 7 and 28 days after herbicide application. Amonio-glufosinate and glyphosate applied isolated or in combinations with other herbicides were effective in controlling B. pilosa independently of the growth stage. The two biotypes demonstrated to be highly resistant to ALS inhibitor herbicides. E. heterophylla showed greater sensitivity to herbicide amonio-glufosinate herbicide and glyphosate in early stages applications. Glyphosate stood out as a satisfactory alternative for controlling E. heterophylla. For this biotype, synergistic effect was verified for associations between amonio-glufosinate and pyrithiobac-sodium.A presença de Bidens pilosa e Euphorbia heterophylla resistentes aos herbicidas inibidores da ALS é um entrave no manejo de plantas daninhas na cultura do algodão, em função da escassez de alternativas de latifolicidas seletivos. Com o intuito de suprir essa carência de informações, foram instalados quatro experimentos em casa-de-vegetação com o objetivo de avaliar herbicidas aplicados em pós-emergência, recomendados para o algodão convencional e transgênico (resistente ao glyphosate e amonio-glufosinate), no controle destes biótipos resistentes. O delineamento experimental utilizado foi inteiramente casualizado com quatro repetições, sendo avaliados 21 tratamentos herbicidas, além de uma testemunha sem aplicação. Instalaram-se dois experimentos por espécie, onde o primeiro correspondeu à aplicação dos herbicidas em estádios de duas a quatro folhas e o segundo de quatro a seis. Avaliou-se os percentuais de controle aos 7 e 28 dias após a aplicação dos herbicidas. Amônio-glufosinate e glyphosate aplicados isolados ou em associações a outros herbicidas foram eficientes no controle de B. pilosa independente do estádio avaliado. Os dois biótipos demonstraram-se altamente resistente aos herbicidas inibidores de ALS avaliados. E. heterophylla demonstrou maior sensibilidade aos herbicidas amonio-glufosinate e glyphosate em aplicações precoces. Glyphosate destacou-se como boa alternativa no controle de E. heterophylla. Para este biótipo, foi verificado efeito sinérgico para as associações entre amonio-glufosinate e pyrithiobac-sodium

Potencial de utilização do clomazone em cultivares de feijoeiro comum

Weed interference can cause severe damages to common bean grain yield. Although the use of herbicides is considered as an efficient means to control weeds, there are just a few alternatives to use in pre-emergence applications. The objective of this work was to evaluate the potential use of pre-emergence applications of clomazone for five cultivars of common bean. Experiments were carried out under greenhouse conditions in a completely randomized design, and the treatments were increasing rates of clomazone (0, 300, 600 and 900 g ha-1) applied to five cultivars of common bean: Diamante Negro, Jalo Precoce, Pérola, BRS Pontal and BRS Radiante. Increased rates of clomazone caused more visual injuries for all varieties. Increased rates of clomazone also inhibited plant growth, chlorophyll content and shoot dry mass for all cultivars except BRS Pontal. Cultivar Jalo Precoce was the most sensitive in relation to all parameters of crop injury. Chlorophyll contents in cv. BRS Radiante at 28 days after crop emergence (DAE) were not changed with increases in clomazone rate. For cv. BRS Pontal, increases in herbicide rate up to 900 g ha-1 did not cause any reduction of crop growth, chlorophyll content and shoot dry mass at 28 DAE.A interferência de plantas daninhas pode causar sérios danos à produtividade da cultura do feijão. Embora o uso de herbicidas seja eficiente no controle dessas espécies, existem poucas alternativas de moléculas para serem utilizadas em pré-emergência da cultura. Objetivou-se com o trabalho verificar a seletividade do clomazone aplicado em pré-emergência em cinco variedades de feijoeiro. Os experimentos foram conduzidos em casa de vegetação em delineamento inteiramente casualizado. Os tratamentos foram constituídos por doses de clomazone (0, 300, 600 e 900 g ha-1) aplicadas em cultivares de feijoeiro (Diamante Negro, Jalo Precoce, Pérola, BRS Pontal e BRS Radiante). Foi verificado que o aumento da dose do herbicida provocou maiores sintomas de intoxicação em todas as cultivares. O incremento da dose também provocou redução na taxa de crescimento da cultura, do teor de clorofila e da massa seca em todos as cultivares, exceto para BRS Pontal. A cultivar Jalo Precoce foi a mais prejudicada nessas variáveis. Aos 28 dias após a emergência (DAE), o teor de clorofila da cv. BRS Radiante não foi alterado com o aumento da dose de clomazone. Para a cv. BRS Pontal, o aumento da dose até 900 g ha-1 não provocou variação na altura aos 28 DAE, no teor de clorofila e na massa seca da parte aérea

Potencial de utilização do dietholate como protetor de clomazone em feijoeiro comum

Safeners are chemicals applied to crops, usually by seed treatment, to improve their tolerance to herbicides. The objective of this research was to evaluate the potential use of dietholate as a safener for pre-emergence applications of clomazone in common beans. Treatments were arranged in a factorial combination 2 x 5 x 6 composed by two herbicide treatments (without or with clomazone at 750 g ha-1), five doses of dietholate (0, 125, 250, 375 and 500 g. a.i. per 100 kg of seeds), and six cultivars (Diamante Negro, Ouro Branco, Jalo Precoce, BRS Pérola, BRS Pontal and BRS Radiante). Dietholate only did not exhibit potential to protect common bean from injuries caused by clomazone, but also increase crop sensibility to the herbicide.Protetores de plantas são produtos químicos usados com a finalidade de aumentar a seletividade de herbicidas. O objetivo deste trabalho foi verificar os efeitos da utilização de dietholathe como protetor para o herbicida clomazone aplicado em pré-emergência na cultura do feijoeiro. Os tratamentos foram arranjados em esquema fatorial 2 x 5 x 6, em que o primeiro fator foi constituído de dois tratamentos herbicidas (sem e com clomazone a 750 g ha-1); o segundo, de doses de dietholate (0, 125, 250, 375 e 500 g i.a. por 100 kg de semente); e o terceiro fator de diferentes cultivares de feijoeiro (Diamante Negro, Ouro Branco, Jalo Precoce, BRS Pérola, BRS Pontal e BRS Radiante). O dietholate não apresentou potencial para proteger as plantas de feijoeiro dos efeitos fitotóxicos do herbicida clomazone, aumentando a sensibilidade das plantas à aplicação do herbicida