Antonio Alberto da Silva

Dinâmica populacional de plantas daninhas sob diferentes sistemas de manejo nas culturas de milho e feijão

Com o objetivo de avaliar a dinâmica populacional de plantas daninhas por meio de parâmetros fitossociologicos, realizou-se este trabalho com as culturas de milho e feijao em cultivos sucessivos, no periodo de novembro de 1998 a maio de 2001, em um Argissolo Vermelho-Amarelo Câmbico, fase terraco, em Vicosa-MG. A comunidade de plantas daninhas era composta por Amaranthus deflexus, Brachiaria plantaginea, Cyperus rotundus, Galinsoga parviflora, Mucuna aterrima e Oxalis latifolia. Os tratamentos foram constituidos de dois sistemas de manejo do solo (plantios convencional e direto) e duas finalidades de uso da cultura do milho (grao e silagem), em blocos com quatro repeticoes. No plantio convencional, antes da semeadura das culturas, o solo foi arado e gradeado, e, no plantio direto, foi realizada a dessecacao das plantas daninhas com herbicidas sistemicos. As avaliacoes de plantas daninhas na cultura do milho foram realizadas antes e apos a aplicacao dos herbicidas nicosulfuron e atrazine em pos-emergencia (aos 20 e 55 DAE, respectivamente) no ano agricola 1999/00, e apos a aplicacao de atrazine e metolachlor em pre-emergencia (aos 20 DAE) em 2000/01. Em se tratando do feijoeiro, as avaliacoes tambem foram feitas antes e apos a aplicacao dos herbicidas fluazifop-p-butil e fomesafen, em pos-emergencia aos 20 e 40 DAE, respectivamente. A dinâmica populacional foi avaliada por meio do uso de parâmetros fitossociologicos baseados na densidade, frequencia e biomassa das especies amostradas. Verificou-se aos 20 DAE, antes da aplicacao dos herbicidas em ambas as culturas (milho e feijao), maior densidade e importância relativa das especies dicotiledoneas no plantio direto. No plantio convencional constatou-se maior densidade, dominância e importância relativa de Cyperus rotundus. Apos aplicacao dos herbicidas seletivos, Cyperus rotundus foi a especie de maior importância relativa em todos os sistemas estudados. Em ambas as finalidades de uso do milho, Cyperus rotundus teve sua populacao reduzida no plantio direto, quando comparado com o convencional.

Estudos anatômicos de folhas de espécies de plantas daninhas de grande ocorrência no Brasil: III - Galinsoga parviflora, Crotalaria incana, Conyza bonariensis e Ipomoea cairica

O objetivo deste trabalho foi estudar a anatomia das folhas das especies de plantas daninhas de grande ocorrencia no Brasil: Galinsoga parviflora, Crotalaria incana, Conyza bonariensis e Ipomoea cairica, visando melhor entendimento sobre as barreiras que cada especie impoe a penetracao dos herbicidas e, assim, fornecer subsidios a busca de estrategias para superar esses obstaculos. As folhas completamente expandidas do terceiro ao quinto no foram coletadas de plantas de ocorrencia espontânea no campo. Das folhas de cada especie foram obtidas tres amostras da regiao central, com aproximadamente 1 cm2, as quais foram utilizadas em estudos da estrutura e clarificacao e em observacoes em microscopio eletronico de varredura (MEV). Todas as especies avaliadas sao anfiestomaticas. A principal barreira foliar potencial a penetracao de herbicidas observada na planta daninha G. parviflora foi a baixa densidade estomatica na face adaxial. C. incana apresentou como possivel principal obstaculo foliar a penetracao de herbicidas o alto teor de cera epicuticular. Ja em relacao a C. bonariensis, alta densidade tricomatica, grande espessura da cuticula da face adaxial e baixa densidade estomatica na face adaxial foram as principais barreiras detectadas. Grande espessura da cuticula da face adaxial e baixa densidade estomatica na face adaxial foram os possiveis obstaculos constatados nas folhas de I. cairica.

Preparation and phytotoxicity of sorgoleone analogues

3,5-Dimethoxybenzylic alcohol was converted into the 2-acetoxy-5-methoxy-3-(pent-1-yl)-1,4-benzoquinone (12), in seven steps, with an overall yield of 14.6%. The natural quinone sorgoleone (1) was isolated from Sorghum bicolor and converted into the corresponding quinone (13) having a saturated side chain. The selective effects of these compounds (1, 12 and 13), at the dose of 5.6 mg of a.i./ g of substrate, on the growth of Cucumis sativus, Lactuca sativa, Desmodium tortuosum, Hyptis suaveolens and Euphorbia heterophylla were evaluated. All three compounds caused some inhibition on the root growth of the test plants (0.0-69.19%) with the aerial parts less affected. The results showed that the triene unit of the sorgoleone side chain is not essential for the phytotoxicity and also the synthetic quinone was as active as the natural product.

Inferências sobre atividade rizosférica de espécies com potencial para fitorremediação do herbicida tebuthiuron

SUMMARY : RHIZOSPHERIC ACTIVITY OF POTENTIALLY PHYTOREME-DIATIVE SPECIES FOR TEBUTHIURON-CONTAMINATEDSOIL The rhizospheric microbial action, accelerating the degradation of compounds in thesoil, is known as phytostimulation. It represents one of the main phytoremediationmechanisms in herbicide-contaminated soil. Tebuthiuron-tolerant plants, which are ableto stimulate their rhizospheric microorganisms, could be highly interesting for thephytoremediation of this herbicide. This study aimed at evaluating the rhizospheric activityof four plant species with phytoremediation potential for tebuthiuron and to infer on thecontribution of the roots to the process of decontamination of this herbicide. The rhizosphericsoil of jackbean ( Canavalia ensiformis ), pearl millet ( Pennisetum glaucum ), Georgia velvetbean (S tizolobium deeringianum ), and black velvet bean ( Stizolobium aterrimum ), plus acontrol treatment (without plant) were analyzed without and with tebuthiuron at 0.73 ig g -1 .The CO

Eficiência de glyphosate no controle de Commelina benghalensis e Commelina diffusa

The weed dayflower, Commelina spp., can survive in a great diversity of environments, what makes its control difficult. In coffee plantations of the Zona da Mata, Minas Gerais - Brazil, glyphosate is repeatedly applied to control weeds, but Commelina benghalensis and C. diffusa have not been successfully controlled. To confirm such fact and to verify the effect of increasing doses of glyphosate (720, 1,400, 2,160, 2,880 and 3,600 g a.i. ha-1) on these weed species, an experiment was installed in a randomized block design with six replications. The rates of herbicide were applied in the flowering period of plants grown in polyethylene boxes 10 cm high, 27.5 cm wide and 39.5 cm long, in unprotected environment. The effectiveness of the treatments was evaluated through the percentage of weed control related to the check treatment (no herbicide), and by the shoot dry biomass that survived the treatments. C. benghalensis was efficiently controlled by glyphosate, but C. diffusa presented herbicide tolerance. The control of C. benghalensis was above 94%, starting from the smallest rate, 25 days after treatments (DAT), and it was 100% in all the doses at 63 DAT. For C. diffusa, in general, as the doses of glyphosate increased, the shoot dry biomass became smaller. However, even with the three higher doses, when up to 98.3% of control at 46 DAT was observed, plant recovery occurred at 88 DAT. Under the conditions of this experiment, glyphosate provided an excellent control of C. benghalensis starting from 720 g a.i. ha-1, 25 DAT. However, excellent control of C. diffusa for over 60 DAT was only achieved with glyphosate rate starting from 2.880 g a.i. ha-1.

Determination of maleic hydrazide residues in garlic bulbs by HPLC

In recent years, the release of information about the preventative and curative properties of garlic on different diseases and their benefits to human health has led to an increase in the consumption of garlic. To meet the requirements of international markets and reach competitiveness and profitability, farmers seek to extend the offer period of fresh garlic by increasing post-harvest life. As a result, the use of maleic hydrazide (1,2-dihydropyridazine-3,6-dione) [MH], a plant growth regulator, has been widespread in various garlic growing regions of the world. The present work was undertaken to develop and validate a new analytical procedure based on MH extraction from garlic previously frozen by liquid nitrogen and submitted to low temperature clean-up. The applicability of the method by analysis of garlic samples from a commercial plantation was also demonstrated. The influence of certain factors on the performance of the analytical methodology were studied and optimized. The approach is an efficient extraction, clean-up and determination alternative for MH residue-quantification due to its specificity and sensitivity. The use of liquid nitrogen during the sample preparation prevents the degradation of the analyte due to oxidation reactions, a major limiting factor. Moreover, the method provides good linearity (r(2): 0.999), good intermediate precision (coefficient of variation (CV): 8.39%), and extracts were not affected by the matrix effect. Under optimized conditions, the limit of detection (LOD) (0.33 mg kg(-1)) was well below the maximum residue level (MRL) set internationally for garlic (15 mg kg(-1)), with excellent rates of recovery (over 95%), good repeatability and acceptable accuracy (CV averaged 5.74%), since garlic is a complex matrix. The analytical performance of the methodology presented was compared with other techniques already reported, with highly satisfactory results, lower LOD and higher recoveries rates. In addition, the extraction process is simple, not expensive, easily executable and requires lower volumes of organic solvent. The proposed methodology removes the need of extensive typical laboratory extraction procedures, reducing the amount of time needed for pesticide analysis and increasing sample throughput. Adopting this method gives food safety laboratories the potential to increase cost savings by a suitable technique in routine testing to determine MH residues in garlic.

Interferência das plantas daninhas na cultura da soja cultivada em dois espaçamentos entre linhas

O presente trabalho teve como objetivo determinar o periodo anterior a interferencia, o periodo total de prevencao da interferencia e o periodo critico de prevencao da interferencia das plantas daninhas na cultura da soja, cultivar UFV-16, nos espacamentos entre linhas de 30 e 60 cm, mantendo-se uma populacao fixa de 400.000 plantas ha-1 nos dois espacamentos. Os tratamentos foram constituidos de dois grupos: em um manteve-se a cultura na ausencia de plantas daninhas em periodos iniciais apos a emergencia da cultura, e, no outro, a cultura foi mantida na presenca de plantas daninhas em periodos iniciais apos a emergencia da cultura. Os periodos foram os seguintes: 0, 10, 20, 30, 40, 50 e 60 dias apos a emergencia, totalizando 14 tratamentos, dispostos em blocos casualizados, com quatro repeticoes. O periodo critico de prevencao da interferencia na soja, considerando a reducao na produtividade de 2%, localizou-se entre o 7o e 53o dia e o 18o e 47o dia para os espacamentos de 30 e 60 cm entre linhas, respectivamente. Assim, para a soja cultivada em menor espacamento entre linhas (30 cm), o controle das plantas daninhas deve ser iniciado mais cedo, quando comparado com espacamento maior nas entrelinhas (60 cm).

Estudos anatômicos de folhas de espécies de plantas daninhas de grande ocorrência no Brasil: IV - Amaranthus deflexus, Amaranthus spinosus, Alternanthera tenella e Euphorbia heterophylla

This research aimed to study the leaf anatomy of the weed species Amaranthus deflexus, Amaranthus spinosus, Alternanthera tenella and Euphorbia heterophylla, widely known in Brazil, to acquire a better understanding of the barriers each species imposes to herbicide penetration, and to other substances used for leaf spraying. Completely expanded leaves from the third to the fifth nodes were collected from spontaneous plants in the field. Three samples approximately 1cm2, were removed from the medium portion of the leaves, from each species. These samples were used for structure, clarification and scanning-electron microscope observations. All species were amphistomatic. The potential major leaf barriers to herbicide penetration in A. deflexus and A. spinosus were, respectively, high cuticle thickness in the adaxial side and high cuticle thickness in both sides, respectively, whereas in A. tenella, high cuticle thickness on both sides, high content of epicuticular wax and high trichome density were the major potential barriers observed. E. heterophylla showed high content of the epicuticular wax, high latex glandular density and high cuticle thickness in the adaxial side as possible major barriers to herbicide penetration.

Effects of herbicide and insecticide interaction on soil entomofauna under maize crop

Abstract The aim of this study was to evaluate the impact of the herbicide mixture nicosulfuron+atrazine, with or without the insecticide chlorpyrifos, onto soil entomofauna under maize crop. The treatments, applied 25 days after maize emergence, were represented by a weeded control without insecticide and herbicide, a weeded control with chlorpyrifos, and mixtures of nicosulfuron+atrazine, with or without chlorpyrifos. Arthropods populations, on the soil surface, as well as inside the soil under maize, were principally represented by mites (Arachnida: Acari), decomposer collembolans (Hexapoda:Parainsecta:Collembola) and predator ants (Hymenoptera:Formicidae). The nicosulfuron+atrazine mixture with chlorpyrifos and the isolated chlorpyrifos reduced the population dynamics of all insect groups on the soil surface compared to the weeded control. In the soil, mite and ant populations were reduced after application of the herbicide mixture with chlorpyrifos and of the isolated chlorpyrifos.The aim of this study was to evaluate the impact of the herbicide mixture nicosulfuron + atrazine, with or without the insecticide chlorpyrifos, onto soil entomofauna under maize crop. The treatments, applied 25 days after maize emergence, were represented by a weeded control without insecticide and herbicide, a weeded control with chlorpyrifos, and mixtures of nicosulfuron + atrazine, with or without chlorpyrifos. Arthropods populations, on the soil surface, as well as inside the soil under maize, were principally represented by mites (Arachnida: Acari), decomposer collembolans (Hexapoda:Parainsecta:Collembola) and predator ants (Hymenoptera:Formicidae). The nicosulfuron + atrazine mixture with chlorpyrifos and the isolated chlorpyrifos reduced the population dynamics of all insect groups on the soil surface compared to the weeded control. In the soil, mite and ant populations were reduced after application of the herbicide mixture with chlorpyrifos and of the isolated chlorpyrifos.

Synthesis and Phytotoxicity Evaluation of Substituted para-Benzoquinones

Sorgoleone (1) is one of the major constituents of sorghum root exudates. Sorgoleone is an allelochemical that reduces the growth of broad-leaf plants. The 3,5-dimethoxybenzylic alcohol (3) was used as starting material for the synthesis of 2-methoxy-6-(non-1-yl)benzo-1,4-quinone (9) in 69% yield. Acetylation of (9) with acetic anhydride gave the triacetate (10) in 82% yield. The triacetate (10) was then converted in two steps in 2-hydroxy-5-methoxy-3-(non-1-yl)benzo-1,4-quinone (11) and 2-acetoxy-5-methoxy-3-(non-1-yl)benzo-1,4-quinone (12) in 8% and 37% yield, respectively. Quinone (11) was obtained also by reaction of (12) with DBU in 63% yield. Alkylation of (3) and oxidation with chromic anhydride formed the new quinones (16) (17) and (18) in 23%, 16% and 12% overall yield, respectively. The effect of these quinones and sorgoleone (1) at concentrations of 5.5 μg g–1 on the development of radicle and aerial parts of Cucumis sativus, Brachiaria decumbens, Hyptis lophanta, and Euphorbia heterophylla was tested.