Competitiveness and genetic characteristics of Conyza bonariensis from Rio Grande do Sul State

Conyza bonariensis (hairy fleabane) is the main glyphosate resistant weeds on soybean crops in Rio Grande do Sul State. The herbicide resistant weeds may have modified their competitive ability, due to the ability to resist the action of the herbicide. Knowledge of weed competitive ability allows us to adopt the best management strategies to improve the crops, without incurring economic losses for farmers. The study aimed to evaluate the competitiveness of biotypes of hairy fleabane in soybean; determine the interference of control periods and coexistence; assess the crop yield loss and the threshold level of glyphosate resistant hairy fleabane biotypes on soybeans; photosynthetic responses between glyphosate resistant and susceptible biotypes; determine changes in photosynthesis and accumulation of shikimic acid in hairy fleabane biotypes under glyphosate effect, and characterize the hairy fleabane diversity occurring in Rio Grande do Sul State. The experimental results show that the cultivar CD 226 RR has a lower competitive ability that hairy fleabane biotypes, and susceptible biotype is more damage to soybean, soybean has a higher oxidative stress when in competition with resistant biotype; cultivar BRS Estância RR has greater competitive ability than horseweed regardless of stage of development, and soy does not suffer from competition for resources of soil, light or both. The Increasing coexistence periods of hairy fleabane with soybean affect the physiological and morphological responses of crop. And the increase in hairy 10 fleabane population impacts negatively crop yield and is more economical control hairy fleabane plants when allocating a greater population. The glyphosate resistant hairy fleabane biotype has better adaptability photosynthetic compared with the glyphosate susceptible population. The effect of glyphosate on the hairy fleabane biotypes is most intense on the glyphosate susceptible biotype, reducing growth and inhibiting completely the photosynthesis variable and EPSPs enzyme. RAPD analysis can be important tool for characterization Conyza species.Conyza bonariensis (buva) é a principal planta daninha resistente ao herbicida glifosato que infesta lavouras de soja no Rio Grande do Sul. As plantas daninhas resistentes a herbicidas podem ter sua habilidade competitiva modificada, em função da capacidade em resistir à ação do herbicida. O conhecimento da habilidade competitiva das plantas daninhas nos permite adotar as melhores estratégias de manejá-las nos cultivos agrícolas, sem que ocorram prejuízos econômicos para os agricultores. O estudo teve por objetivo avaliar a competitividade de biótipos de buva com a cultura da soja; determinar a interferência dos períodos de controle e de convivência; avaliar a perda da produtividade e o nível de dano econômico (NDE) de biótipos de buva resistentes ao herbicida glifosato sobre a cultura da soja; respostas fotossintéticas entre biótipos resistentes e suscetíveis ao herbicida glifosato; determinar alterações nas fotossíntese e acúmulo de ácido chiquímico em biótipos de buva sob efeito do glifosato; e caracterizar a diversidade de biótipos de buva ocorrentes no RS. Os resultados dos experimentos evidenciam que a cultivar de soja CD 226 RR possui menor habilidade competitiva que os biótipos de buva, e o biótipo suscetível apresenta maior dano à cultura da soja; a soja apresenta maior estresse oxidativo quando em competição com biótipo resistente; a cultivar de soja BRS Estância RR possui maior habilidade competitiva que a buva independente do estádio de desenvolvimento, e a soja não sofre com a competição por recursos de 8 solo, luz ou ambos. Períodos crescentes de convivência de buva com a soja afetam as respostas morfológicas e fisiológicas da cultura. E o incremento da população de buva impacta negativamente a produtividade da cultura e é mais econômico controlar as plantas de buva quando se distribuem em maior população. O biótipo resistente de buva apresenta melhor adaptabilidade fotossintética comparado com o biótipo suscetível. O efeito de glifosato sobre os biótipos de buva é mais intenso sobre o biótipo suscetível, reduzindo o crescimento e inibindo completamente as variáveis fotossintéticas e a enzima EPSPs. A técnica de RAPD pode ser importante ferramenta para caracterização de espécies de Conyza

Development stages horseweed in soybeans competition

ABSTRACT: The objective of this study was to evaluate the relative competitive ability of soybean with different development stages of hairy fleabane. Two experiments were conducted in greenhouse, in a completely randomized design. In the experiment it was tested soybean and hairy fleabane competition at different stage of development (rosette and 15 cm height) at the proportions 100:0, 75:25, 50:50, 25:75 and 0:100, and total plant population was 315 plant m-2. The variables evaluated were plant height, leaf area, and shoot dry matter (leaves and stems). Competitive analysis was performed by diagrams and interpreting the competitiveness index. The soybean has greater competitive ability that horseweed for both development stages. The intraspecific competition is more intense for soybean when in hairy fleabane rosette stage, and the competitive relations are equivalent between soybean and hairy fleabane of 15 cm tall. The both hairy fleabane stages were injured in the soybeans competition

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

<div><p>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.</p></div

Efeito do Residual de Atrazina e Atrazina + Simazina em Soja

The soil persistence of herbicides from the triazines group is basically dependent on precipitation conditions and soil characteristics. The objective of this study was to assess the residual effect of different application times and atrazine and atrazine + simazine doses for the soybean crop. Experiments were conducted in the field and greenhouse. In the field, the design of subdivided plots with four replications was used, with factor A composed of application times 56, 49, 42, 35, 28, 21, and 14 days before soybean sowing; and factor B, by the herbicides atrazine and atrazine + simazine. For the greenhouse experiment, the design was completely randomized blocks, factor A doses 0, 570, 1140, 1715, 2285, 2860, 3430, and 4000 g i.a. ha-1, factor B herbicides atrazine and atrazine + simazine. The application of the treatments was carried out with a CO2 pressurized sprayer, after the application of the soybean. The field was assessed regarding the plant stand, phytotoxicity, stature, height of insertion of the first training, chlorophyll content, and kg ha-1 yield. In the greenhouse, phytotoxicity, plant height, leaf area, and dry mass were assessed. Then, data were submitted to analysis of variance and, when significant, the means were compared by the Tukey test at 5%. The residual simulation of the herbicides atrazine and atrazine + simazine in the soil showed similar behavior regarding the effects on soybean. In the field experiment, due to the high precipitations that occurred in the interval between herbicide applications and soybean sowing, no phytotoxic effects or reduction in crop yield were observed. In the greenhouse, increasing the residual dose of herbicides in the soil increased the toxic effects on soybean.A persistência no solo de herbicidas do grupo das triazinas é dependente de basicamente de condições de precipitação e características do solo. Objetivou-se avaliar o efeito residual de diferentes épocas de aplicação e doses de atrazina e atrazina + simazina para a cultura da soja. Conduziram-se experimentos a campo e casa de vegetação. A campo utilizou-se o delineamento de parcelas subdivididas com quatro repetições, sendo o fator A composto por épocas de aplicação 56, 49, 42, 35, 28, 21 e 14 dias antes da semeadura da soja; e fator B, pelos herbicidas atrazina e atrazina + simazina. Para o experimento em casa de vegetação o delineamento inteiramente casualizados, o fator A foi constituído de doses 0, 570, 1.140, 1.715, 2.285, 2.860, 3.430 e 4.000 g i.a.ha-1; e fator B pelos herbicidas atrazina e atrazina + simazina. A aplicação dos tratamentos foi realizada com pulverizador costal pressurizado por CO2, após a aplicação realizou-se a semeadura da soja. A campo avaliou-se o estande de plantas, fitotoxicidade, estatura, altura de inserção do primeiro entrenó, teor de clorofila e produtividade. Em casa de vegetação foram avaliados fitotoxicidade, estatura de plantas, área foliar e massa seca. Após os dados foram submetidos a análise de variância e quando significativas as medias foram comparadas pelo teste Tukey a 5%. A simulação de residual dos herbicidas atrazina e atrazina + simazina no solo apresentam comportamento similares quanto aos efeitos na soja. No experimento a campo, devido às altas precipitações ocorridas no intervalo entre as aplicações dos herbicidas e a semeadura da soja, não foram observados efeitos fitotóxicos ou redução na produtividade da cultura. Em casa de vegetação, o aumento da dose residual dos herbicidas no solo incrementou os efeitos tóxicos na soja

IMPACT OF THE COMPETITION DURATION ON LIGHT AND SOIL RESOURCES BETWEEN SOYBEAN AND VOLUNTEER CORN

The RR volunteer corn emerged as a problematic weed in the soybean rotation system. In the early crop stages, the requirement resources for growth is little and enough to crop and weeds, however the light competition could triggering morphological changes in response to changes in light reflected from neighboring. The objective of this study was to evaluate the impact of duration of competition for light and soil resources between soybean and volunteer corn. The treatments were competition conditions between soybean and corn as competitor: control, light competition and soil+light competition; and duration of competition: at V3 and V5 soybean growth stages. The results of this study demonstrate that duration and resource of competition with volunteer corn influenced the response on soybean growth and development. The soybean not displayed characteristic of shade avoidance syndrome in light competition. The light competition changes the soybean shoot: root length ratio and root length. In early competition, the soybean growth and development are unaffected for light or soil+light resource in competition. However, in later duration of competition, light and soil+light have similar reduction on effects on soybean growth, development and photosynthetic pigments. 

Weed incidence and sowing time affect soybean development

Despite the economic importance of the effects of weeds on the plastochron and emission of nodes of soybean plants, it has not been studied in detail. The aim of this study was to provide information about the effects of weeds on the development of soybean plants by determining the plastochron and number of nodes of soybean plants of different cultivars sown at different times in soils with presence and absence of weeds. A field study was conducted during the 2013/2014 crop season including a phytosociological survey to identify the occurring weeds, and the determination of the plastochron and final number of nodes of soybean plants. Four botanical families of weeds were found infesting the soybean crops. The plastochron and final number of nodes of soybean were influenced by the cultivar, sowing time, and presence of weeds. The plastochron was higher when the plants were grown in the presence weeds due to the higher relative frequency, relative density, relative abundance, and importance value index of the Euphorbia heterophyla, Ipomoea purpurea, and Urochloa plantaginea species, which resulted in a slower development of the soybean plants, and lower number of nodes per plant

Pesticide occurrence in groundwater near irrigated rice fields

Submitted by Paula Gautério ([email protected]) on 2014-02-12T22:33:17Z No. of bitstreams: 1 Ocorrência de agrotóxicos em águas subterrâneas de áreas adjacentes a lavouras de arroz irrigado.pdf: 223427 bytes, checksum: f1e4d4c15ed0f3dee9e8151907dcf25c (MD5)Approved for entry into archive by Gabriela Silva da Rosa ([email protected]) on 2014-02-22T21:18:33Z (GMT) No. of bitstreams: 1 Ocorrência de agrotóxicos em águas subterrâneas de áreas adjacentes a lavouras de arroz irrigado.pdf: 223427 bytes, checksum: f1e4d4c15ed0f3dee9e8151907dcf25c (MD5)Made available in DSpace on 2014-02-22T21:18:33Z (GMT). No. of bitstreams: 1 Ocorrência de agrotóxicos em águas subterrâneas de áreas adjacentes a lavouras de arroz irrigado.pdf: 223427 bytes, checksum: f1e4d4c15ed0f3dee9e8151907dcf25c (MD5) Previous issue date: 2011The objective this study was to monitor pesticide residues in groundwater at three different times and in seven regions producing rice in southern Brazil, in the 2007/08 season. Imazethapyr and fipronil were found in all regions studied. All groundwater samples from the Planície Costeira Interna to Lagoa dos Patos and Santa Catarina contained at least one pesticide. The lowest number of contaminated samples were detected in the Southern region. The highest frequency of contaminated samples was found after drainage of the rice fields. Only fipronil exceeded limits of potability, in 27% of samples, according European Community criteria

Ocorrência de agrotóxicos em águas subterrâneas de áreas adjacentes a lavouras de arroz irrigado

The objective this study was to monitor pesticide residues in groundwater at three different times and in seven regions producing rice in southern Brazil, in the 2007/08 season. Imazethapyr and fipronil were found in all regions studied. All groundwater samples from the Planície Costeira Interna to Lagoa dos Patos and Santa Catarina contained at least one pesticide. The lowest number of contaminated samples were detected in the Southern region. The highest frequency of contaminated samples was found after drainage of the rice fields. Only fipronil exceeded limits of potability, in 27% of samples, according European Community criteria