RESUMO -A presente pesquisa objetivou estudar os efeitos dos períodos de controle e de convivência de uma comunidade infestante sobre as características produtivas da soja nos sistemas de semeadura direta (SSD) . Tolerando cinco por cento de perda na produtividade da cultura, constatou-se que os períodos críticos de prevenção da interferência foram dos 33 aos 66 DAE para o cultivar CD 201 no SSD e dos 34 aos 76 DAE para o cultivar M-SOY-6101 no SSC. A interferência das plantas daninhas durante todo o ciclo da cultura reduziu, em média, 46% (SSD) e 32% (SSC) a produtividade de grãos da soja. Não houve efeito das plantas daninhas na estatura das plantas, na altura de inserção da primeira vagem e no número de vagens por planta.Palavras-chave: competição, Glycine max, períodos de controle. ABSTRACT -This work aimed to determine the interference of weed communities in crop yield INTRODUÇÃOA cultura da soja const itui-se na mais importante oleaginosa cultivada no mundo. No âmbito mundial, o Brasil é o segundo maior produtor e um dos principais exportadores dos grãos. A soja está sujeita a uma série de fatores que podem influenciar o seu desenvolvimento e a produção. As plantas daninhas acarretam perda s na produtiv idade devido, principalmente, à competição por luz, nutrientes e água, além de dificultarem a colheita. Atuam também

Protodioscin, a steroidal saponin, was isolated from the extract as the major component and the activities of this compound were in good agreement with those found for the extract. The release of this compound into the soil is a plausible explanation for the decrease in production observed in transgenic soybean crop after desiccation of U. ruziziensis. © 2017 Society of Chemical Industry.

RESUMO -Com o objetivo de avaliar os efeitos de períodos de dessecação de Urochloa ruziziensis na implantação e na produtividade da soja transgênica no sistema de plantio direto, foram conduzidos dois experimentos em campo, nos municípios de Colina-SP, no ano agrícola de 2007/08, e Jaboticabal-SP, em 2009/10. Em Colina, utilizou-se uma área de pastagem de U. ruziziensis, conduzida há sete anos. Nesse local foram testados quatro períodos de dessecação da cobertura vegetal: 30, 20, 10 e 0 dias antes da semeadura da soja. No experimento de Jaboticabal, a área utilizada tinha histórico de pastagem com U. ruziziensis, que no ano agrícola 2008/09 foi cultivada com milho. Após a colheita do milho ocorreu reinfestação natural de U. ruziziensis na área, correspondendo a mais de 80% de cobertura vegetal. Nesse experimento, os tratamentos corresponderam a seis períodos de dessecação: 25, 20, 16, 12, 7 e 0 dias após a aplicação. Nos dois experimentos utilizou-se 1,44 kg e.a. ha -1 do herbicida glyphosate e o cultivar de soja M-SOY 7908 RR. O delineamento experimental foi o de blocos ao acaso, com quatro repetições. Foram avaliados o estande da cultura aos 20 dias após a semeadura da soja e na pré-colheita, a altura de plantas, a altura de inserção da primeira vagem, o número de vagens por planta e o rendimento de grãos (produtividade estimada em kg ha). Os resultados foram submetidos à análise de variância (teste F), com as médias sendo comparadas pelo teste de Tukey a 5% de probabilidade. A dessecação de U. ruziziensis no mesmo dia da semeadura da soja reduziu a altura das plantas, o número de vagens por planta e a produtividade de grãos. O período recomendado para o manejo químico de U. ruziziensis com glyphosate está entre 10 e 20 dias antes da semeadura da soja. Pôde-se concluir que o período de dessecação de U. ruziziensis alterou a produtividade da cultura.Palavras-chave: Brachiaria ruziziensis, Glycine max, cobertura vegetal, alelopatia, glyphosate.ABSTRACT -Two field trials were carried out to evaluate the effects of burn-down timing of Urochloa ruziziensis on transgenic soybean establishment and yield under the no-tillage system. One experiment was conducted in Colina, SP -Brazil, in 2007 season, and the other in Jaboticabal, SPBrazil, 2009/2010 season. In 2007, the experiment was carried out in a 7-year-old grass pasture of U. ruziziensis, with four burn-down timings of vegetation cover being tested 30, 20, 10, and 0 days in advance to soybean sowing. In 2009/2010, the experiment was conducted in an old grass pasture of U. ruziziensis cropped with maize the summer before. After maize harvesting, a natural re-infestation of U. ruziziensis occurred, corresponding to more than 80% of the vegetation cover. In this experiment, treatments corresponded to six burn-down timings of vegetation cover 25, 20, 16, 7, and 0 days in advance to soybean sowing. In all experiments, 1.44 kg a.e. ha -1 of herbicide glyphosate was applied, and the soybean cultivar M-SOY 7908 RR was used. The experiments were arranged in a randomized ...

Farmers of the Franca region in Brazil observed that Bidens sulphurea was able to eliminate the Panicum maximum weed, which infected coffee plantations, without affecting the crop. In an effort to determine if the inhibitory effects observed were due to the presence of phytotoxic compounds from leaves and roots, a biodirected isolation and spectroscopic characterization has been carried out. The leaf dichloromethane and root acetone extracts were the most active, and the former appeared to be more phytotoxic to the target species, including four weeds. A total of 26 compounds were isolated from leaves and roots, and four of them are described here for the first time. The major compounds in the leaf extract are the sesquiterpene lactones costunolide, reynosin, and santamarine, and these showed marked inhibition. Amaranthus viridis and Panicum maximum were the most sensitive species of the weeds tested. These three phytotoxic lactones were also evaluated on A. viridis and P. maximum under hydroponic conditions. A. viridis was the most affected species with the three lactones, and santamarine was the most phytotoxic compound on both. This is the first time that the phytotoxicity of sesquiterpene lactones has been evaluated on hydroponic culture. The work described here is a preliminary approach for the use of B. sulphurea for weed control in agriculture, both as a cover crop and by use of its components as natural herbicide leads.

The objective of this study was to evaluate the effects of the drift of ripeners (sulfometuron-methyl, ethephon and trinexapac-ethyl) on the initial growth of Eucalyptus urograndis. The experimental design was a randomized block with seven treatments (control; sulfometuron-methyl 0.9 and 1.2 g i.a. ha -1 ; ethephon 28.8 and 38.3 g i.a ha -1 ; trinexapac-ethyl 15 and 20 g i.a. ha -1 ) with four replicates using each plant as an experimental plot. We evaluated the effects 7, 14, 21, 28, 35 and 42 days after application, when we determined the length, diameter, total leaf area and total dry mass of the stem. The application of sulfometuron-methyl may have resulted in an effect known as "hormesis" due to an increasing trend in stem growth. The application of trinexapac-ethyl resulted in greater increases in the leaf dry mass and leaf area compared with those caused by the other ripeners that were used in this study, most likely due to the loss of apical dominance. The application of ethephon had no significant effect on the plants.

Young eucalyptus seedlings in general are sensitive to stress factors during early development and establishment. Weed competition is one of the major biotic effects contributing to reductions on the initial growth of eucalyptus plants. This study aimed to evaluate the effects of different densities and distances of Urochloa decumbens seeded and regrowth during the early growth of Eucalyptus urograndis. Two experiments were conducted in an open and semi-controlled area, in a completely randomized design, in factorial arrangement 4 x 2 + 1, being respectively, four densities of weed plants (2.6, 5.2, 7.8 and 10.4 plants m -²), two distances between Eucalyptus and weeds (5 and 15 cm), and a weed-free control. The height and diameter of eucalyptus were evaluated 15 days intervals, and at the end of 90 days after eucalyptus planting (DAP) the leaf area and dry mass were measured. For a density of U. decumbens plants that were seeded at a density of 2.6 plants m -2 , 90 days after Eucalyptus planting (DAP), there was a decrease in the height (20%), stem diameter (10%), leaf area (55%) and dry mass (48%). For the regrowth of U. decumbens at a density of 2.6 plants m -2 at 90 DAP, the height (47%), stem diameter (55%), leaf area (89%) and dry mass (87%) decreased. The results demonstrate that U. decumbens adversely affected the growth of eucalyptus, without statistical differences between distances, and weeds in regrowth affecting Eucalyptus growth more than seeded weeds.

RESUMO -Objetivou-se com este trabalho avaliar o efeito da redução do espaçamento entre fileiras nos períodos de interferência e na produtividade do amendoim rasteiro (Arachis hypogaea). O experimento foi instalado no município de Jaboticabal-SP. Os tratamentos constaram de dois espaçamentos entre fileiras (80 e 90 cm), divididos em dois grupos. No primeiro, as plantas daninhas foram controladas desde a emergência até 0 (interferência constante), 30, 45, 60, 82, 97 e 112 dias depois. No segundo, as plantas daninhas conviveram com a cultura pelos mesmos períodos do grupo anterior. O delineamento experimental adotado foi o de blocos casualizados, em arranjo de parcelas subdivididas, com quatro repetições. As principais plantas daninhas presentes na área foram Digitaria sp., Xanthium strumarium, Acanthospermum hispidum e Cenchrus echinatus. Para uma perda tolerável de 5% de produtividade, o período crítico de prevenção à interferência foi dos 27 aos 76 e dos 35 aos 96 dias após a emergência para os espaçamentos de 80 e 90 cm, respectivamente; a queda de produtividade das parcelas mantidas com interferência de plantas daninhas em relação àquelas no limpo foi superior a 80%, independentemente do espaçamento.Palavras-chave: Arachis hypogaea, competição, período crítico de prevenção à interferência.ABSTRACT -The aim of this research was to evaluate the effect of reducing the spacing between rows in periods of weed interference and peanut (Arachis hypogaea) yield. The experiment was carried out in Jaboticabal, Brazil. Treatments consisted of two row spacings (80 to 90 cm), divided into two groups. In the first group, the weeds were controlled since emergence up to 0 (constant interference), 30, 45, 60, 82, 97 and 112 days. In the second group, the weeds were allowed to grow with the peanut culture during the same periods. The experiment was arranged in a randomized block design with treatments in split-plots, with four repetitions. The main weeds in the area were Digitaria sp., Xanthium strumarium, Acanthospermum hispidum and Cenchrus echinatus. To an acceptable yield loss of 5%, the critical period of interference control was from 27 to 76 and from 35 to 96 days after emergence for spacing rows of 80 and 90 cm, respectively; yield reduction at the non-controlled weed plots compared to the interference-free plots was more than 80%, regardless of row spacing.

Weed herbicide resistance has been a challenge in agriculture. The objective of this study was to detect sourgrass (Digitaria insularis (L.) Fedde) glyphosate-resistant plants and to evaluate the growth and polymorphism rate between the resistant and susceptible biotypes, as a subsidy for the integrated management of species. An experiment was conducted primarily for the detection of weed resistance using increasing doses of glyphosate to generate a dose-response curve. Then, an experiment consisting of eight treatments (destructives analysis of growth) and five replications was conducted to characterize and compare the phenological stages of each biotype. In addition to visual assessments, the dry weight and leaf area, absolute and relative growth rates, net assimilation rate and leaf area ratio of plants were determined. Finally, polymorphism among biotypes was determined using inter simple sequence repeat molecular markers. A resistant factor of 3.12 was found among the biotypes. The resistant biotype grew faster and was more robust than the susceptible biotype, arriving first to flowering. The resistant biotype was better adapted to light interception. The 25 inter simple sequence repeat molecular markers analysis showed a polymorphism rate of 56.6% among the analyzed biotypes.