Weed Development Stages Research Articles

Control of ALS- and EPSPS-Resistant Amaranthus palmeri by Alternative Herbicides Applied in PRE- and POST-Emergence

ABSTRACT: The emergence of resistant biotypes of the Amaranthus palmeri species in cotton production areas of the state of Mato Grosso, Brazil, generated the need for correct identification of this species and information on viable herbicidal tools for their management. Thus, greenhouse experiments were conducted to evaluate the efficacy of alternative herbicides applied to A. palmeri in pre and post emergence. A randomized block design with four replications was used. The efficacy of herbicides applied in pre emergence was evaluate in two experiments, one in a clayey and other in a sandy soil; 9 herbicide treatments (8 with herbicide application and a control without application) were applied on each soil. Subsequently, two experiments with different populations of A. palmeri were conducted, using a 13 x 2 factorial arrangement, to evaluate the efficacy of herbicides applied in post emergence. The factors consisted of 13 herbicide treatments (12 with herbicide application and a control without application) and two weed development stages (2-4 and 6-8 leaves). Pre-emergence application of the flumioxazin, S-metolachlor, isoxaflutole, and trifluralin herbicides controlled the weed satisfactorily in both evaluated soils. The sulfentrazone and metribuzin herbicides were effective in the sandy soil, and diuron was effective in the clayey soil. The clomazone herbicide did not successfully controlled the A. palmeri plants in any of the soils. All post-emergence herbicide treatments were effective for the management of A. palmeri plants, when they were applied at the 2-4 leaf stage.

Soybean yield loss and economic thresholds due to glyphosate resistant hairy fleabane interference

ABSTRACT: The interference of glyphosate resistant hairy fleabane (Conyza bonariensis) has caused yield losses in soybean crop. Knowledge of the economic threshold is an important aspect for the economic management of resistant weeds. Because of it, the interference of the glyphosate resistant hairy fleabane density on the soybean yield loss was evaluated, as well as to estimate the economic threshold. Two experiments were conducted to verify the effect of different weed densities on the yield of two soybean cultivars (BRS Estância and BMX Turbo). Weed density ranged from 0 to 124 plants m-2. The yield of the BRS Estância decreased by 1.4% to the increase of one single plant, while for the BMX Turbo the loss was 25.9%. Soybean yield and economic threshold were lower for the BMX Turbo cultivar compared to the cultivar BRS Estância, which can be attributed to the genotype, competitive ability, weed development stage and/or environment. Increases in crop yield expectation, soybean price and herbicide efficiency reduce the economic threshold, indicating that the adoption of control measures should be taken when the weed density is low. Due to the high cost of hairy fleabane control, it is only feasible at high densities.

Effect of different doses of post-emergence-applied iodosulfuron on weed control and grain yield of malt barley (Hordeum distichum L.), under Mediterranean conditions

AbstractA study was carried out over a two year period (2009/2010 and 2012/2013) on an experimental farm in the Alentejo region (Beja), in southern Portugal where rainfed malt barley (Hordeum distichum L.) is sown at the end of autumn or beginning of winter (November- December). The aim of this experiment was to study the efficiency of the herbicide iodosulfuron-methyl-sodium to control post-emergence broadleaved weeds in this cereal crop. The malt barley crop was established using no-till farming. This technology provides the necessary machine bearing capacity of the soil to assure the post-emergence application of herbicides at two different weed development stages. The herbicide iodosulfuron-methyl-sodium was applied at three doses (5.0, 7.5, and 10.0 g a. i. · ha-1) and at two different broadleaved weed development stages (3 to 4 and 6 to 7 pairs of leaves), that also corresponded to two different crop development stages (beginning of tillering and complete tillering). The results indicated that early herbicide application timing provided a significantly higher efficiency for all the applied herbicide doses, but this better weed control was not reflected in a higher crop grain yield. The lack of a higher crop grain yield was probably due to a crop phytotoxicity of the herbicide, when used at an early application timing.

Alternatives for chemical management of sourgrass

Intensive use of Glyphosate has been selected multiple resistant sourgrass biotypes in the areas of intensive agriculture in Brazil. Thus, it is important that viable management alternatives are evaluated for this invasion, which currently is regarded as the main problem of Brazilian agriculture. The study aimed to evaluate strategies for chemical management of sourgrass. Three trials divided according to the weed development stages were performed: Post-Initial (up to tillering), Post-Delayed (one to four tillers) and Adult-Plant (adult stage characterized by the beginning of the reproductive phase). The sourgrass seeds were collected from biotypes with evidence of Glyphosate tolerance in the municipality of Rio Brilhante – MS. In each trial were evaluated thirteen treatments and one witness, where the treatments were herbicide mixtures applications with subsequent sequential applications at different dates (7, 10 and 14 days after the first application) and the herbicides application without mixtures. Sourgrass plants are tolerant to Glyphosate and Clethodim herbicides. Formulated mixtures of Paraquat + Diuron and Haloxifop are the most suitable for controlling sourgrass plants derived from seeds, regardless of the control period. Treatments that have the Haloxyfop herbicide in the first application provided better control when compared to the other treatments with mixtures and sequential applications at all stages of applications.

Redução de doses de herbicidas no controle de plantas daninhas em cultivo de cevada sob condições climáticas temperadas

Yield losses in cereal crops under temperate climate conditions due to weed-crop competition, namely Lolium rigidum G., can reach up to 80%, depending on the season and infestation level. Nevertheless, the costs of chemical weed control and the environmental impact caused by herbicides recommend the search for strategies to reduce their input. Therefore, the aim of this work was to study the possibility of reducing the input of different post-emergence herbicides (diclofop-methyl + fenoxaprop–p-ethyl and amidosulfuron + iodosulfuron-methyl-sodium) to control Lolium rigidum G. and broad-leaf weeds in barley under no-till, and to monitor the effect on weed population levels and crop yields. A field experiment was carried out in 2007-2008 and 2008-2009, in an experimental farm in the south of Portugal, combining different herbicide doses applied at different weed development stages. Results show that, for all herbicide doses, the earlier application provides higher weed control efficacy and higher grain yields, indicating that the reduction of doses is possible while maintaining satisfactory cropgrain yields.

Effect of reduced doses of mesosulfuron + iodosulfuron to control weeds in no-till wheat under Mediterranean conditions

Field experiments were carried out over three years (2004-05, to 2006-07) to study the efficacy of a post-emergence dual-purpose herbicide (mesosulfuron - methyl (3%) + iodosulfuron - methyl - sodium (0.6%) + mefenpyr - diethyl (9%) to control Lolium rigidum Gaud. and broad-leaved weeds in no-till wheat (Triticum aestivum L.). A ready herbicide mixture was used at three doses (6+1.2, 9+1.8 and 12+2.4 g a.i./ha) on two dates (beginning of tillering for L. rigidum and 2-3 pair of leaves for broad-leaved weeds, and complete tillering for L. rigidum and 5-6 pair of leaves for broad-leaved weeds) with three different application volumes (100, 200 and 300 L/ha). The results of the present study reveal that using lower than the recommended dose (12+2.4 g/ha), the herbicide mixture controls L. rigidum better than it controls some broad-leaved weeds. Effective weed control, which was achieved mainly through the application at the first weed development stage, provided higher grain yields. The lower control efficacy of more developed L. rigidum and broad-leaved weeds and a longer period of competition between crop and weeds are responsible for the significantly lower crop yields for the delayed application. Within each application timing significant differences were obtained among the dose/volume combinations, with the exception of the first application regarding L. rigidum control, indicating that a reduction in herbicide dose is possible, but only for certain dose/volume combinations. Nonetheless, weed control was maintained across an array of dose/volume combinations, especially with L. rigidum, thus, our results demonstrate that reduced doses can effectively control weeds if applied early.

Contribution des méthodes de lutte mécanique au désherbage intégré des grandes cultures oléagineuses

The integrated approach of weed management refers to a combination of direct and indirect methods in order to limit chemical applications. In oilseed rape, sunflower and soybean, mechanical weed control can be an alternative or a complement to herbicides and should take progressively a larger place in the direct weed control options, taking into account of the policy of restriction of chemical use. CETIOM launched a research program to assess, in different backgrounds, the selectivity and the efficacy of three tools, used either alone or combined with herbicides: the rotary hoe, the finger weeder and the in-row hoe. As an alternative or a complement to herbicides, mechanical weed control strategies were selective enough for oil crops if they were used in appropriate conditions (crop stage, soil surface moisture, adjustments of the tools). Linked with long term preventive measures to maintain weed population at a low level, they could be as efficient as herbicides but with an irregularity and strongly dependent on weed development stage. These techniques could be economically competitive but require often more working time. Mechanical management can thus be an answer to some of the new requirements of the agricultural context but operator skill, experience and knowledge are critical to success. Introducing these weed control methods in a farm requires a deep change of state of mind which appears today as a major restraint for the farmers.

Effect of reduced doses of a post-emergence graminicide to control Avena sterilis L. and Lolium rigidum G. in no-till wheat under Mediterranean environment

The study was carried out over 2 years (2004–2005 and 2005–2006) in a private farm in the Alentejo region (Évora), in the south of Portugal where rainfed wheat is sown after the beginning of the winter rainfall season. The wheat crop used for this study was established using no-till, as this technology provides the necessary machine-bearing capacity of the soil to assure post-emergence application of herbicides at different weed development stages. A mixture of clodinafop+cloquintocete was applied using three different dosages and volumes on two dates. The results indicate that lower herbicide doses than those recommended by the manufacturer were sufficient to achieve a high Avena sterilis L. and Lolium rigidum G. control efficiency and consequently potential grain yield, when the treatments were carried out on an early application date (beginning of tillering). When the herbicide application was delayed (complete tillering) it was necessary to increase the herbicide dose in order to achieve the highest grain yield. There was a positive and significant correlation between weed control efficiency and grain yield, but the respective correlation coefficient was not very high. This is because at the first application stage, both weeds and crop were more sensitive to the herbicide and consequently there was some crop phytotoxicity caused by the herbicide when its concentration increased. Weed reinfestation was low for both application dates, indicating that lower herbicide doses than the recommended ones can be used for satisfactory control of A. sterilis L. and L. rigidum G.

Controlo de infestantes em trigo de sementeira directa utilizando doses de herbicida e volumes de calda reduzidos

The aim of the present work was to assess the effect of lower doses than recommended by the manufacturer of the herbicide diclofopmethyl + fenoxaprop – p - ethyl + mefenpyr – diethyl and different application volumes to control the grass weeds Avena sterilis L. and Lolium rigidum G. in post-emergence in no-till wheat and the consequent effect on crop yield. Therefore lower herbicide doses than recommended (1; 1.5 and 2 l ha-1) were combined with lower application volumes (100; 200 and 300 l ha-1) at two different weed development stages (beginning of tillering and complete tillering). The recommended herbicide doses to control these weeds vary between 2.5 and 3 l ha-1 and the application volumes should vary between 350 and 600 l ha-1 . The results show that the anticipation of the herbicide application (beginning of tillering) leads to a better weed control even using herbicide doses and application volumes lower than recommended. The lower efficiency to control more developed grass weeds and a longer period of competition between crop and weeds for the second application timing (complete tillering) were responsible for the lower crop yields for this application date.

Effect of reduced doses of a post-emergence herbicide to control grass and broad-leaved weeds in no-till wheat under Mediterranean conditions

A study was carried out over two years (2004/2005 and 2005/2006) on a private farm in the Alentejo region (Évora), in the South of Portugal where rainfed wheat is sown at the start of the winter rainfall season. The wheat crop was established using no-till as this technology provides the necessary machine bearing capacity of the soil to assure the post-emergence application of herbicides at different weed development stages. Mesosulfuron-methyl (3%) and iodosulfuron-methyl-sodium (0.6%) and mefenpyr-diethyl (9%) were used at three doses and two dates with three different application volumes. The results of this study indicate that using lower doses than recommended (0.4 kg ha −1) this herbicide controls the annual grass weeds ( Avena sterilis L. and Lolium rigidum G.) better than some broad-leaved weeds. For all doses and volume combinations, the application at the first weed development stage (beginning of tillering for grass weeds and 3–4 pairs of leaves for broad-leaved weeds) provided higher grain yields. The lower efficiency of control of more developed grass and broad-leaved weeds and a longer period of competition between crop and weeds for the second application date (complete tillering for grass weeds and 5–6 pairs of leaves for broad-leaved weeds) were responsible for the significantly lower crop yields for this application date. Within each application date no significant differences were obtained between all dose/volume combinations, indicating that the reduction of dose is possible. At the later application date, the lower herbicide dose seems to require a lower application volume to provide maximum grain yield.

Efeito de doses reduzidas de um herbicida de pós-emergência no controlo de infestantes e na produção de trigo em sementeira directa

The purpose of this work was to study the efficiency of the herbicide Mesosulfuron & iodosulfuron & mefenpyr – diethyl, to control grass and broad-leaved weeds at post-emergence in wheat under direct drilling, combining three doses of herbicide (0,20; 0,30 e 0,40 kg/ha) with three water volumes (100; 200 e 300 l/ha), in two different weed development stages (beginning and complete tillering for the grass weeds and 3-4 and 5-6 pairs of leaves for the broad-leaved weeds). For our climatic and infestation conditions, the recommended doses are 0,30; 0,35 and 0,40 kg/ha, and the recommended water volumes vary between 350 and 600 l/ha. The study was carried out during the year of 2004/2005 on a private farm near Evora (South of Portugal). The results showed a great efficiency of this herbicide to control grass weeds. The efficiency to control broad-leaved weeds was lower than to control grass weeds, but for both weed types, the first application timing was better than the second one. The results indicate the possibility of the anticipation of the application of this herbicide to allow both reduction of doses and water volumes while maintaining the crop yield.

Aplicação do fomesafen via água de irrigação por aspersão no controle de Euphorbia heterophylla

A aplicação de herbicidas via água de irrigação (herbigação) por aspersão, especialmente por pivô central, vem crescendo no Brasil. O objetivo deste estudo foi investigar a eficácia de doses de fomesafen aplicado via água de irrigação por aspersão no controle de Euphorbia heterophylla. Os tratamentos foram dispostos no esquema fatorial (4 x 3 x 2) + 3, sendo quatro doses do fomesafen (60, 120, 180 e 240 g ha-1), três estádios de desenvolvimento de E. heterophylla (1, 7 e 14 dias após a emergência - DAE), dois métodos de aplicação (pulverização e herbigação) e testemunhas sem herbicida (uma para cada estádio de desenvolvimento da planta daninha). Foi empregado o delineamento inteiramente casualizado, com quatro repetições. Cada unidade experimental constou de um vaso com 4,0 L de solo, onde foram distribuídas 50 sementes dessa planta daninha. A pulverização foi feita com 200 L ha-1 de calda; na herbigação foi usada lâmina de água de 4,72 mm, aplicada por simulador de irrigação. E. heterophylla foi mais suscetível ao fomesafen com 1 DAE. Neste estádio, a herbigação controlou-a melhor que a pulverização nas doses de 180 e 240 g ha-1. Na aplicação aos 7 DAE, geralmente a pulverização foi mais eficaz que a herbigação, mas o controle da planta daninha não foi satisfatório. Aplicado com 14 DAE, o herbicida, independentemente da dose e do método de aplicação, proporcionou controle pobre ou nenhum.

Effect of reduced doses of a post-emergence graminicide mixture to control Lolium rigidum G. in winter wheat under direct drilling in Mediterranean environment

A study was carried out over 2 years (2002/2003 and 2003/2004) on a private farm in the Alentejo (Évora), in the South of Portugal where rainfed wheat is sown after the beginning of the winter rainfall season. A no-till wheat crop was used as this technology provides the necessary soil bearing capacity for the post-emergence application at different weed development stages. A mixture of diclofop-methyl+fenoxaprop- p-ethyl+mefenepir-diethyl was used at three doses on two timings with three different application volumes. The results indicate that lower herbicide concentrations using higher water application volumes decreased weed control efficiency at both weed development stages. For every treatment, the first weed development stage (beginning of tillering) provided a higher crop grain yield. At this stage, both weeds and crop are more sensitive to the herbicide and as consequence the higher weed control efficiency was not reflected in a higher grain yield, due to some crop fitotoxicity caused by the herbicide when its concentration increased. Weed reinfestation was low for both application timings, indicating that lower herbicide doses than the recommended ones (2.5–31 ha −1) or those normally used by the Portuguese farmers (21 ha −1) can be used for a satisfactory control of Lolium rigidum G. In winter wheat post-emergence treatments can reduce doses if combined with adequate application volumes and early application timings. When herbicide application was delayed (complete tillering) higher herbicide doses were necessary to achieve the highest crop yield.

Dose econômica ótima de acifluorfen + bentazon para controle de picão-preto e guanxuma em soja

As doses dos herbicidas são estabelecidas para uso em uma ampla variação de condições ambientais e de manejo das culturas. Contudo, algumas vezes, as doses de herbicidas podem ser reduzidas e, ainda assim, a interferência das plantas daninhas com a cultura pode ser suprimida. O objetivo deste trabalho foi testar a redução de dose para o herbicida acifluorfen + bentazon no controle de picão-preto (Bidens spp.) e guanxuma (Sida rhombifolia), em diferentes estádios de desenvolvimento das plantas daninhas, em relação à época de emergência da soja. Para isso, foi conduzido experimento em campo, em Passo Fundo - RS, cujos tratamentos constaram de quatro doses do herbicida (1,25; 1,5; 1,75; e 2,0 L ha-1), aplicadas em cinco combinações de estádios de desenvolvimento da cultura e das plantas daninhas, além de duas testemunhas, uma sem controle das plantas daninhas e outra em que estas foram arrancadas manualmente nas mesmas datas das aplicações/herbicidas. Considerando-se todas as situações testadas, o grau de controle de guanxuma variou entre 80 e 99% e o de picão-preto entre 78 e 99%. Constatou-se, para as duas espécies-alvo, que o melhor controle, considerando todo o ciclo, foi a aplicação em plantas daninhas com quatro folhas. Os resultados obtidos mostram que o incremento na dose de acifluorfen + bentazon, na faixa de 1,25 a 2,0 L ha-1, resulta em retorno linear positivo, em termos de produtividade da soja. A dose de rótulo de 2,0 L ha-1 foi a que se mostrou biologicamente mais eficaz; já doses próximas a 75% da dose de rótulo foram as que compensaram, economicamente, a adoção do controle.