A.A. Silva

Interferência de plantas daninhas sobre a produtividade da mandioca (Manihot esculenta)

O manejo inadequado das plantas daninhas e uma das principais causas da baixa produtividade da cultura da mandioca no Brasil. Objetivou-se com este trabalho identificar as especies de plantas daninhas infestantes da cultura da mandioca e o grau de interferencia que estas exercem sobre o cultivo, em funcao do periodo de convivencia com a cultura. Dois experimentos foram realizados em areas adjacentes, no municipio de Vicosa-MG, utilizando-se o cultivar Cacauzinha, do grupo das mandiocas mansas. O delineamento experimental adotado foi em blocos casualizados, com sete tratamentos e quatro repeticoes. Os tratamentos do primeiro experimento foram compostos por periodos iniciais de convivencia da cultura com as plantas daninhas: 25, 50, 75, 100 e 125 dias apos o plantio (DAP); no segundo experimento, as plantas de mandioca, inicialmente, permaneceram livres das plantas daninhas pelos mesmos periodos. Em ambos os experimentos adotou-se o espacamento de 1,0 x 0,5 m, sendo a area util da parcela constituida pelas duas linhas centrais, deixando-se 1,0 m em cada extremidade como bordaduras frontais, totalizando 8,0 m2. As plantas daninhas foram avaliadas aos 25, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325 e 350 DAP. As caracteristicas produtividade de raizes, peso da parte aerea, indice de colheita, teor de amido e materia seca das raizes foram avaliadas aos 12 meses apos o plantio. As especies de plantas daninhas que predominaram na area experimental foram: Bidens pilosa, Raphanus raphanistrum, Cyperus rotundus e Commelina benghalensis, com a primeira delas predominando em quase todas as epocas de coletas. Os periodos de convivencia com as plantas daninhas nao interferiram nos indices de colheita, teor de amido e materia seca das raizes. Todavia, considerando a produtividade de raizes, o final do periodo anterior a interferencia foi proximo dos 25 dias, e o periodo critico de prevencao da interferencia situou-se entre 25 e 75 DAP. Cultivos realizados apos 75 DAP nao afetaram as caracteristicas da cultura da mandioca avaliadas.

Persistência e lixiviação de ametryn e trifloxysulfuron-sodium em solo cultivado com cana-de-açúcar

The aim of the work was to evaluate the behavior of the ametryn + trifloxysulfuron-sodium commercial mixture in sugar-cane crop, as related to leaching potential and persistence in the environment. The Typic Haplufalf soil area was divided into two sub areas where the sugar-cane varieties SP 79 1011 and SP 80 1816 were cultivated. The treatments were constituted by pre and post-emergence applications of the commercial herbicide mixtures in 2003 and 2003 + 2004, with four soil samplings 0-0.10 and 0.10-0.20 m deep. Bioassay and High Performance Liquid Chromatography (HPLC) methods were used to evaluate the residues. Both methods were found satisfactory for evaluation of the commercial mixture residue, although the bioassay use did not allow evaluating the compounds separatedly. According to the data obtained from the simultaneous analysis of ametryn and trifloxysulfuron-sodium by HPLC, most of the ametryn residues remained in the soil layer 0-0.10 m deep, persisting for over 180 days after application (DAA), in soil sprayed in 2003 + 2004. Ametryn residues in 0.10 - 0.20 m deep, were as well found for the treatments sprayed in 2003 + 2004 and showed the risks of leaching and contaminating water with this herbicide. For the treatments sprayed only in 2003, a significant residual effect was not detected 490 days after application. Differences in residual effect among cultivated sub areas with the variety SP 79 1011 and SP 80 1816 were due to the different amounts of clay and organic matter in the soil. Residues of trifloxysulfuron-sodium were not found in any period of the soil sampling, as the limit of quantification by HPLC (0.06 mg L-1) is higher than the used dose of this herbicide (37 g ha-1).

Densidades de plantas daninhas e épocas de controle sobre os componentes de produção da soja

This work aimed to evaluate the effects of different weed densities on the yield components of soybean grain, cv. BRS 243 RR. The experimental design was arranged in completely randomized blocks, and the treatments consisted of increasing periods of control and three weed densities (low, medium and high). The initial periods of control were: 0, 0-5, 0-10, 0-15, 0-21, 0-28, 0-35, 0-42, 0-49 and 0-125 (harvesting). In low infestation areas, the weed community was composed mainly of Brachiaria plantaginea, Ipomoea nil, Euphorbia heterophylla and others. In medium and high infestation areas, the outstanding weeds were Brachiaria plantaginea, Ipomoea nil, Digitaria horizontalis, Cyperus rotundus and others. B. plantaginea was responsible for the highest dry matter accumulation in all levels of infestation. Regarding the crop yield components, number of pods per plant was the most severely affected by competition, reduced at about 58% in the low infestation area, 71% in the medium infestation area and 78% in the high infestation area. Number of seeds per pod and weight of 1000 grains were less influenced by competition; however, these parameters were reduced, indicating a relation between weed control periods and infestation level with soybean yield component.

Período anterior à interferência na cultura da soja-RR em condições de baixa, média e alta infestação

The aim of this study was to evaluate the period before weed interference in soybean culture, cv. BRS 243-RR, under low, medium and high weed density. The experimental design was arranged in complete randomized blocks, and the treatments consisted of increasing periods of weed control (0, 0-5, 0-10, 0-15, 0-21, 0-28, 0-35, 0-42, 0-49 and 0-125 days). In low weed infestation area the main weed species were: Brachiaria plantaginea,Ipomoea nil,Euphorbia heterophylla. In medium and high infestation areas, Brachiaria plantaginea,Ipomoea nil,Digitaria horizontalis and Cyperus rotundus were the most frequent weeds. Considering 5% and 10% of tolerance of soybean grain yield reduction, it was concluded that the period before interference was 17 and 24 days after emergence (DAE) in low infestation, area 11 and 15 DAE in medium infestation area and 11 and 16 DAE in high infestation area. Weed interference during the full crop cycle reduced soybean grain yield in 73%, 82% and 92%, for low, medium and high weed density, respectively.

Manejo de plantas daninhas na cultura da mandioca

A mandioca (Manihot esculenta) e cultivada em varios paises, sendo de grande importância como fonte de energia para alimentacao humana e animal e na geracao de empregos e renda. No Brasil, apesar de essa cultura apresentar alto potencial produtivo - em alguns estudos alcancando valores superiores a 100xa0txa0ha-1 de raizes - , a produtividade nacional e baixa, atribuida em grande parte ao manejo inadequado das plantas daninhas. A interferencia dessas plantas resulta em competicao pelos recursos essenciais, como nutrientes, agua e luz. Alem disso, o controle realizado de maneira incorreta das plantas daninhas nos mandiocais dificulta outros tratos culturais e aumenta os custos de producao. Nesta revisao sao abordados os aspectos relativos ao manejo das plantas daninhas na cultura, descrevendo, de forma detalhada, os principais componentes de interferencia. Discute-se, em varias situacoes, o periodo critico de competicao. Por fim, sao apresentados os principais metodos de controle visando a utilizacao do manejo integrado como forma sustentavel do controle de plantas daninhas nessa cultura.

Estudos anatômicos de folhas de espécies de plantas daninhas: II - Bidens pilosa, Emilia sonchifolia, Ageratum conyzoides e Sonchus asper

This research aimed to study leaf anatomy in the widely common Brazilian weed species Bidens pilosa, Emilia sonchifolia, Ageratum conyzoides and Sonchus asper, to acquire a better understanding of the barriers each species imposes upon herbicide penetration, and provide information on how to overcome these obstacles. The completely expanded leaves from the third to the fifth nodes were collected from plants spontaneously occurring in the field. From the leaves of each species, three samples with approximately 1 cm2 were taken at the central portion and used for structure, and clarification studies and scanning-electron microscope (SEM) observations. All species were found to be amphistomatic. The main leaf barriers against herbicide penetration in B. pilosa were found to be high trichome density and low stomatic density in the adaxial side. High content of epicuticular wax, high cuticle thickness in the adaxial side and low stomatic density on both sides were the herbicide barriers observed in the leaves of E. sonchifolia, while in A. conyzoides the barrier was low stomatic density in the adaxial side. S. aspers main leaf barriers were low stomatic density in the adaxial side and high epiderm thickness in the adaxial side.

Efeitos de culturas na persistência de herbicidas auxínicos no solo

The objective of this work was to develop techniques to reduce, in soil, the persistence of herbicides used in pastures, to implement crop-breeding system integration and subsequent crops. Thus, experiments were performed under greenhouse and field conditions. The first one under field conditions (degraded pasture), aimed to evaluate the tolerance of maize and sorghum crops to herbicides (picloram + 2,4-D) and 2,4-D, applied at commercial recommended rates. The second experiment conducted under greenhouse conditions aimed to evaluate the residual effect of these herbicides under different area management conditions. Nine treatments were assessed, with the main plots being composed by the crops (without soil cultivation, grown with corn and grown with sorghum) and by the subplots, management (weeds controlled by manual cultivation, with 2,4-D, or with a mixture picloram + 2,4-D). The field experiment was installed in Vicosa-MG in hot and humid season in a completely randomized block design, with four replications. The soil was a Red-Yellow Ultisol with median fertility. For the implementation of the second experiment under greenhouse conditions, soil samples collected in all subplots of the first experiment were used at 1, 42, 125 and 170xa0days after application (DAA) of herbicides. In this study, the persistence of the herbicides in the soil at each treatment was evaluated to identify soil remediation ability by maize and sorghum, compared with bare soil. It was found that corn plant growth was affected by the herbicides and accumulated lesser amount of dry mass when the corn plants were grown in soil with residues of picloram + 2,4-D mixture, while sorghum was tolerant. The residual effect of the herbicides in the soil evaluated was not influenced by the crop species or soil management (corn, sorghum or bare soil). There was not any sign of poisoning in the indicative plants grown in soil samples collected in the areas treated with 2,4-D in the evaluation conducted 42 DAA. However, plants grown in soil samples that received the mixture picloram + 2,4-D, showed no intoxication symptoms only after 150xa0DAA.

Interferência de plantas daninhas em diferentes densidades no crescimento da soja

Este trabalho foi realizado com o objetivo de avaliar os efeitos de densidades de plantas daninhas (baixa, media e alta infestacao) sobre as variaveis de crescimento da soja, cv. BRS 243RR. O delineamento experimental foi de blocos ao acaso, sendo os tratamentos constituidos por dez periodos de convivencia das plantas daninhas com a cultura (0, 0-5, 0-10, 0-15, 0-21, 0-28, 0-35, 0-42, 0-49 e 0-125 dias). As variaveis estudadas foram altura de plantas, massa seca dos ramos desprovidos de folha, massa seca das folhas, numero de folhas e area foliar da soja. As avaliacoes foram determinadas no final do periodo de interferencia, juntamente com a avaliacao de densidade e acumulo de fitomassa da comunidade infestante. Na area onde a soja foi cultivada sob baixa infestacao de plantas daninhas, observou-se aumento da densidade das infestantes em funcao do tempo apos a emergencia da soja. Todavia, o contrario foi observado nas areas de media e alta infestacao; nelas verificou-se reducao da densidade das plantas daninhas ao longo do periodo de avaliacao. A altura e area foliar das plantas de soja foram influenciadas pelo nivel de infestacao, o que nao foi observado para massa seca e numero de folhas. Conclui-se que o nivel de infestacao afeta de maneira diferenciada as variaveis que definem o crescimento da soja.

Effects of glyphosate and endosulfan on soil microorganisms in soybean crop

A soja resistente ao glyphosate e a cultura transgenica mais cultivada em todo o mundo. Pesquisas envolvendo o impacto de mistura de herbicidas e inseticidas e seus efeitos sobre microrganismos do solo sao raramente reportadas. Este trabalho teve por objetivo avaliar o impacto do herbicida (glyphosate), do inseticida (endosulfan) e da mistura de ambos sobre a atividade microbiana do solo na cultura da soja. O delineamento experimental foi em blocos casualizados, com quatro tratamentos e cinco repeticoes. Os tratamentos foram o herbicida glyphosate 480 SL [540 g de ingrediente ativo (i.a.) ha-1], endosulfan 350 EC (525xa0gxa0i.a.xa0ha-1), a mistura de glyphosate 480 SL (540xa0gxa0de i.a.xa0ha-1) com endosulfan 350xa0EC (525xa0gxa0i.a.xa0ha-1) e a testemunha onde se aplicou agua. A atividade microbiana foi avaliada aos cinco dias apos a aplicacao dos tratamentos. A aplicacao de glyphosate nao afetou a producao de CO2 pela microbiota do solo. A aplicacao de endosulfan (isolado ou em mistura com o glyphosate) reduziu a producao de CO2 pelos microrganismos do solo. A biomassa microbiana e o quociente metabolico foram menores nos tratamentos submetidos a aplicacao de endosulfan isolado e em mistura com glyphosate, em comparacao aqueles submetidos a aplicacao de glyphosate isolado e a testemunha.

Época de dessecação anterior à semeadura sobre o desenvolvimento da aoja resistente ao glyphosate

The objective of this paper was to evaluate the best timing for Brachiaria brizantha desiccation with glyphosate, aiming at transgenic soybean sowing. Different desiccation times were established (2.880 g ha-1 of glyphosate) ranging from 21 to zero days before soybean sowing, with one (1.080 g ha-1) or two (1.080 + 1.080 g ha-1 ) glyphosate applications in postemergence, respectively at 15 and 40 days. At five days after the first application and during flowering, foliate number and dry matter, dry matter of the remaining aerial part, roots, and radicular nodules were evaluated. During the same time, soil samples were collected to determine basal respiration rate and microbial biomass. At the end of the cycle, soybean grain yield was determined according to the different treatments. Soybean growth was affected by postemergence application of glyphosate, decreasing plant dry matter. Soybean development improved when glyphosate was used for desiccation between 7 and 21 days before sowing. Higher negative impact against microbial biomass occurred when desiccation and sowing were performed at the same day. Without glyphosate application, control grain yield decreased in more than 40%, and, on average, 23% on the plants that received the herbicide in postemergence.