Resumo -O objetivo deste trabalho foi avaliar a resistência de capim pé-de-galinha (Eleusine indica) ao glifosato, em lavouras de soja transgênica; avaliar o efeito de aplicações de glifosato em diferentes estádios de desenvolvimento; identificar práticas agronômicas associadas à seleção de biótipos resistentes; e avaliar a eficiência dos herbicidas cletodim, fluazifope-P-butílico, clomazona, glufosinato de amônio e glifosato nas plantas resistentes. Plantas escapes ao tratamento com glifosato foram coletadas em 24 propriedades, no Rio Grande do Sul. As plantas foram cultivadas em casa de vegetação, tendo-se avaliado a sua resistência ao glifosato. Os acessos resistentes foram selecionados e avaliados quanto ao efeito da aplicação do glifosato em diferentes estádios de crescimento e quanto à sensibilidade aos herbicidas. Foi aplicado um questionário aos produtores para identificação das práticas agronômicas associadas às falhas no controle. O controle de E. indica pelo glifosato é mais efetivo com a aplicação em estádios iniciais de desenvolvimento. Práticas agronômicas, como uso contínuo de baixas doses do herbicida, aplicação em estádios de desenvolvimento avançados das plantas daninhas (mais de um afilho) e a ausência de rotação de culturas foram relacionadas às falhas de controle observadas. Os herbicidas cletodim, fluazifope-P-butílico e glufosinato de amônio são alternativas eficientes para o controle de E. indica.Termos para indexação: Eleusine indica, Glycine max, dosagem, eficiência de controle, estádio fenológico, resistência ao glifosato, roundup ready. Management of goose grass on transgenic soybean, resistant to glyphosateAbstract -The objective of this work was to evaluate the resistance of goose grass (Eleusine indica) to glyphosate application in transgenic soybean crops; evaluate the effect of glyphosate applications in different growth stages; identify the main agronomic practices associated with the selection of resistant biotypes; and evaluate the effect of the herbicides clethodim, fluazifop-p-butyl, clomazone, glufosinate ammonium, and glyphosate on resistant plants. Plants that survived glyphosate application were collected on 24 properties in the state of Rio Grande do Sul, Brazil. Plants were grown in greenhouse and their resistance to glyphosate was evaluated. The resistant accessions were selected and evaluated as to the effect of glyphosate application on different growth stages and to their sensitivity to the herbicides. A questionnaire was given to producers in order to identify agronomic practices associated with control failures. The control of E. indica by glyphosate is more effective at initial growth stages. Agronomic practices, such as continued use of low doses of glyphosate, application on advanced weed growth stages (more than one tiller), and absence of crop rotation were related to the observed control failures. The herbicides clethodim, fluazifop-p-butyl, and glufosinate ammonium are efficient alternatives to control E. indica.

Yellow nutsedge (Cyperus esculentus) is adapted to flooding and reduces yield in irrigated rice. Information on the competitive ability of this weed with the crop and the size of the economic damage caused is lacking. Mathematical models quantify the damage to crops and support control decision-making. This study aimed to determine yield losses and economic thresholds (ET) of this weed in the culture according to weed population and time of onset of irrigation of the crop. The field study was conducted in the agricultural year of 2010/2011 in Pelotas/RS to evaluate the competitive ability of BRS Querência in competition with different population levels of yellow nutsedge and two periods of onset of flood irrigation (14 and 21 days after emergence). The hyperbolic model satisfactorily estimated yield losses caused by yellow nutsedge. Population of yellow nutsedge was the variable most fitted to the model. The delay of seven days for the beginning of rice irrigation causes decrease in competitive ability of BRS Querência, and based on the ET calculated to the price paid for rice, it is necessary between two and thirteen plants m -2 weed to justify the control in the first and second period of irrigation, respectively. Increases in yield, price paid for rice and control efficiency of the herbicide, besides reduction of costs of controlling promote reduction of ET of yellow nutsedge in rice crops, justifying the adoption of control measures even at smaller weed population.Key words: Cyperus esculentus, Oryza sativa, rectangular hyperbole.Perdas de produtividade e níveis de dano econômico de tiririca-amarela em arroz irrigado em função do início da irrigação por inundação Resumo A tiririca-amarela (Cyperus esculentus) é adaptada ao alagamento e causa redução de produtividade do arroz irrigado. Informações da habilidade competitiva da planta daninha com a cultura e a dimensão do prejuízo econômico por ela causado são escassas. Modelos matemáticos quantificam prejuízos às culturas e subsidiam a tomada de decisão de controle. O objetivo deste estudo foi determinar perdas de produtividade e níveis de dano econômico (NDE) da tiririca-amarela na cultura em função da população da planta daninha e da época de início da irrigação da cultura. Foi conduzido estudo a campo, na safra 2010/2011, no município de Pelotas, RS, para avaliar a habilidade competitiva da cultivar de arroz BRS Querência em competição com diferentes níveis populacionais de tiririca-amarela em duas épocas de início de irrigação da cultura (14 e 21 dias após a emergência). O modelo hiperbólico estimou satisfatoriamente as perdas de produtividade que a tiririca-amarela causa à cultura. A variável mais ajustada ao modelo foi a população de tiririca-amarela. O atraso de sete dias no início da irrigação do arroz causa decréscimo na habilidade competitiva da cultivar BRS Querência, sendo necessárias, com base nos NDE calculados à variável preço pago pelo arroz, entre duas e 13 plantas m -2 da planta daninha para justificar o controle na primeira e segunda...

In the last growing seasons, goosegrass (Eleusine spp.) control failures have been observed following application of glyphosate on Roundup Ready® soybean in Rio Grande do Sul (RS) - Brazil, suggesting this species' resistance to the herbicide. Thus, the objectives of this study were to identify the occurrence of goosegrass resistance to the herbicide glyphosate in RS; and to determine the predominant species of the genus Eleusine, as well as the LD50 and GR50 of the suspected resistant biotypes. Two experiments were conducted under greenhouse conditions: one to identify the biotypes resistant to glyphosate, and the other, a dose-response curve experiment, as well as a study of the botanical characteristics of the species. In the first experiment, 39 biotypes were tested, mainly Eleusine indica, collected with suspected resistance to glyphosate. The glyphosate dose was 2,160 g e.a. ha-1, and the control was evaluated at 28 days after treatment. All biotypes were effectively controlled,with the biotypes from the municipality of Boa Vista do Incra showing greater tolerance. Two biotypes suspected of resistance (12.1 and 12.3) and a susceptible biotype in a dose-response experiment were tested at the following doses: 0, 135, 270, 540, 1,080, 1,620, and 2,160 g e.a. ha-1. The results of this experiment showed that biotype 12.1 does not present resistance to glyphosate and biotype 12.3 has a low level resistance since it is effectively controlled by the herbicide at the maximum dose.

Clearfield™ (CL) rice (Oryza sativa L.) is a weedy rice (Oryza spp.; synonym = red rice) control tool that has been used in Brazil since 2003. This system includes the use of an imidazolinone (IMI)-tolerant cultivar and the application of IMI herbicides. In this review article, Brazilian weed scientists evaluate the challenges and lessons learned over 18 yr of CL use. CL system benefits include selective weedy rice control, better crop establishment during the most advantageous period of the year, and more efficient fertilizer use. In Rio Grande do Sul state, the CL system, in conjunction with other improvements, has contributed to rice grain yield gains from 5,500 kg ha−1 before 2002 to around 8,400 kg ha−1 currently. In contrast, the main problem that has arisen over this period is the rapid evolution of IMI-resistant weedy rice, caused by gene flow from CL rice cultivars. The off-label use (rate and continuous use) of IMI herbicides has contributed to the evolution of resistance in Echinochloa spp. and other weeds. IMI herbicide carryover has also affected susceptible crops grown after CL rice. Crop rotation with soybean [Glycine max (L.) Merr.] is increasing, ensuring system sustainability. The importance of minimum tillage has also become apparent. Such cultivation includes applying nonselective herbicides before sowing or just before crop emergence (at the spiking stage to eliminate as much weedy rice as possible and other weeds at an early growth stage). It also includes the use of certified seeds free of weedy rice, following label instructions for IMI herbicides, applying the herbicide PRE followed by POST, and complementary weedy rice management practices, such as roguing of surviving weedy rice plants.

Among the species of the genus Cyperus occurring in paddy rice, C. esculentus, C. difformis and C. iria are the most important, and the latter two are reported as resistant to herbicides in Rio Grande do Sul (RS). The aim of this work was to characterize and mapping the occurrence of resistant plants of the genus Cyperus in areas of paddy rice in RS State, and to analyze the agronomic factors that interfere in the resistance selection. Seeds from individual plants were harvested in the 2014/15 crop, characterized as control failures by the application of acetolactate synthase inhibitors (ALS), totaling 43 samples. At the time of collection, the grower was inquired on aspects related to the management of weeds in the crop. Seeds were germinated in BOD and when seedlings were in two leaves stage they were transplanted into 0.3 L pots containing substrate. When the plants had 4-6 leaves, imazapyr + imazapic was spray at the registration rate. Thirty days after application, control of the tested biotypes was evaluated, converting the data to binary scale, where zero (0) and one (1) correspond to susceptibility and resistance, respectively. The agronomic factors that denote the high selection pressure of resistant biotypes are the consecutive use of Clearfield® technology, the use of higher doses than the registration and the low crop rotation adoption. Although not mentioned as one of the main weeds, it is observed that almost half of the samples collected from plants of the genus Cyperus are resistant to the ALS inhibitors, distributed in almost all the growing regions.

This research aimed to evaluate the phytosociology of weeds in irrigated rice in different soil management systems and crop rotation intensity. Therefore, two field studies were carried out. Study 1 was conducted in an area that has been cultivated since 1994 with three cultivation systems: direct, pre-germinated and conventional ones. Study 2 was carried out in an experimental area in five Integrated Farming Systems, with crop rotation. Phytosociological evaluations were conducted when rice was fully blooming, in the first study, and when grain filling was ending, in the second study. Pre-germinated system of rice cultivation has predominance of aquatic weeds. Conventional system when compared with direct sowing has lower weed densities. Integrated Agricultural Production Systems with higher intensity of crop rotation have been higher infested of perennial species.

A stakeholder survey was conducted from April through June of 2018 to understand stakeholders perceptions and challenges about cropping systems and weed management in Brazil. The dominant crops managed by survey respondents were soybean (73%) and corn (66%). Approximately 75% of survey respondents have grown or managed annual cropping systems with two to three crops cultivated per year in succession. Eighteen percent of respondents manage only irrigated cropping systems, and over 60% of respondents adopt no-till as a standard practice. According to respondents, the top five troublesome weed species in Brazilian cropping systems are horseweed (asthmaweed, Canadian horseweed and tall fleabane), sourgrass, morningglory, goosegrass, and dayflower (Asiatic dayflower and Benghal dayflower). Among the nine species documented to have evolved resistance to glyphosate in Brazil, horseweed and sourgrass were reported as the most concerning weeds. Other than glyphosate, 31 and 78% of respondents manage acetyl-CoA carboxylase (ACCase)-inhibitor and/or acetolactate synthase (ALS)-inhibitor resistant weeds, respectively. Besides herbicides, 45% of respondents use mechanical, and 75% use cultural (e.g., no-till, crop rotation/succession) weed control strategies. Sixty-one percent of survey respondents adopt cover crops to some extent to suppress weeds and improve soil chemical and physical properties. Nearly 60% of survey respondents intend to adopt the dicamba or 2,4-D resistant crops when available. Results may help practitioners, academics, industry and policy makers better understand the bad and the good of current cropping systems and weed management practices adopted in Brazil, and adjust research, education, technologies priorities and needs moving forward.

The objective of this study was to investigate the relative competitive ability of barley crop with the weed species of black oat or radish. Three experiments were conducted under greenhouse at UFPel in a completely randomized design, with four replications, and treatments arranged in a replacement series. The proportions of barley plants and competitors of black oat or wild radish were: 100:0, 75:25, 50:50, 25:75 and 0:100, always with a total population of 578 and 770 plants m -2 for black oat and wild radish, respectively. The variables evaluated were plant height; leaf area and shoot dry mass. Statistical analysis was performed by applied diagrams to the replacement series and interpretations of competitiveness indices. Barley has superior competitive ability to radish but below the oat. For barley, the interspecific competition with oat is more harmful, while in competition with wild radish has independent if competitor is own crop or weed.Additional keywords: Avena strigosa; Hordeum vulgare; interference; Raphanus sativus. ResumoO objetivo deste trabalho foi investigar a habilidade competitiva relativa da cultura da cevada com as espécies daninhas aveia-preta ou nabo. Foram realizados três experimentos em casa de vegetação, em delineamento completamente casualizado, com quatro repetições, sendo os tratamentos arranjados em série de substituição. As proporções de plantas de cevada e dos competidores aveia-preta ou nabo foram: 100:0, 75:25, 50:50, 25:75 e 0:100, com população total de 578 e 770 plantas m -2 , para aveia-preta e nabo, respectivamente. As variáveis avaliadas foram estatura, área foliar e massa seca da parte aérea. A análise estatística foi realizada por diagramas aplicados aos experimentos substitutivos com as interpretações dos índices de competitividade. A cevada apresenta habilidade competitiva superior ao nabo, mas inferior à aveia-preta. Para a cevada, a competição interespecífica com aveia-preta é mais prejudicial, enquanto que em competição com nabo independe se o competidor é própria cultura ou a planta daninha.