A.F.L. Machado

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.

Growth analysis of Digitaria insularis

Digitaria insularis is a perennial species that reproduces from seeds and rhizomes, being difficult to control after its first flowering. In order to define integrated management techniques to this species, its growth was evaluated under greenhouse conditions, using a pot filled with 0.003 m3 of soil. Height, leaf area and dry matter evaluations were carried out between 14 and 112 days after emergence (DAE), every 7 days, at 15 different times. The experiment was arranged in a completely randomized block design, with four replications. The plant was fragmented into root+rhizome, stem and leaf. After drying at 70 oC, leaf area and dry matter were determined. Highest leaf area and dry matter values were verified at 98 and 105 DAE, respectively. Leaves showed higher participation in dry matter total accumulation followed by roots+rhizome, up to 105 DAE. Dry matter accumulation of Digitaria insularis slowed down up to 45 DAE, increasing due to rhizome formation. Relative growth rate values decreased along time due to higher photo assimilate accumulation. Digitaria insularis showed slow growth up to 45 DAE, increasing from 45 to 105 DAE, suggesting the possibility of good cultural control by crops that have fast initial growth and large leaf area, covering the soil rapidly.

Efeitos de sistemas de manejo sobre a população de tiririca

Em experimento conduzido em campo, de novembro de 1998 a maio de 2001, sobre Argissolo Vermelho-Amarelo Câmbico de alta fertilidade, em Vicosa-MG, foram avaliados os efeitos de sistemas de manejo do solo na populacao de tiririca (Cyperus rotundus). Na area experimental, antes da instalacao do experimento predominava infestacao alta (720 ± 130 plantas m-2) de tiririca. 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), cultivados com feijao de outono-inverno em sucessao a cultura do milho, 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 glyphosate + 2,4-D. As avaliacoes das manifestacoes epigeas da tiririca na cultura do milho ocorreram aos 20 e 55 dias apos a emergencia (DAE) no ano agricola 1999/00 e aos 20 DAE em 2000/01 e, para o feijoeiro, aos 20 e 40 DAE. A avaliacao do banco de tuberculos foi realizada apos a colheita do milho, no ultimo ano de conducao, determinando-se a densidade, a biomassa e a porcentagem de brotacao dos tuberculos coletados. Verificou-se reducao das manifestacoes epigeas da tiririca no sistema de plantio direto em ambas as finalidades de uso da cultura do milho durante todo o periodo de conducao do ensaio. Tanto no milho cultivado para grao quanto para silagem, constatou-se elevada reducao do banco de tuberculos no plantio direto, com predominio de tuberculos dormentes, em relacao ao plantio convencional.

Leaf anatomy and morphometry in three eucalypt clones treated with glyphosate

This work aimed to evaluate the effects of simulated drift of glyphosate on the morphoanatomy of three eucalypt clones and to correlate the intoxication symptoms on a microscopic scale with those observed in this visual analysis. The effects of glyphosate drift were proportional to the five doses tested, with Eucalyptus urophylla being more tolerant to the herbicide than E. grandis and urograndis hybrid. The symptoms of intoxication which were similar for the different clones at 7 and 15 days after application were characterized by leaf wilting, chlorosis and curling and, at the highest rates, by necrosis, leaf senescence and death. Anatomically glyphosate doses higher than 86.4 g.ha-1 caused cellular plasmolysis, hypertrophy and hyperplasia, formation of the cicatrization tissue and dead cells on the adaxial epidermis. The spongy parenchyma had a decrease, and the palisade parenchyma and leaf blade thickness had an increase. The increased thickness in leaf blade and palisade parenchyma may be related to the plant response to glyphosate action, as a form of recovering the photosynthetically active area reduced by necroses and leaf senescence caused by the herbicide.

Crescimento do eucalipto sob efeito da deriva de glyphosate

The possible negative effects of glyphosate drift on eucalyptus plants throughout their cycle are one of the many issues faced in forestry. Thus, 120 plants presenting variable degrees of intoxication were randomly selected at day 30 after application of 1.440 g ha-1 glyphosate, aiming to control the weeds in an area of Eucalyptus grandis x E. urophylla (urograndis hybrid) at 120 days after transplantation. The treatments were constituted by the following intervals: 0-5; 6-10; 11-20; 21-30; 31-40 and 41-50% of plant intoxication with 0-5% being considered the control treatment. Height and diameter were evaluated after plant selection, up to 360 days after application (DAA) and the intoxication symptoms were evaluated during this period. At 360 DAA wood volume (m3) was estimated and height and diameter gains were calculated. Plants with initial intoxication above 31% presented lesser height and diameter at 270 DAA Height gains were lesser in plants with initial intoxication above 41%. Lesser diameter was observed from 21% intoxication, with the plants with 41-50% intoxication displaying the lesser values for diameter growth. The damage caused by the drift affected wood production at 270 DAA, with the plants with 21-30, 31-40 and 41-50% intoxication being the ones presenting reduced wood volume of 18, 26 and 48%, respectively, in relation to the control treatment. The results confirmed the damage caused by glyphosate drift to eucalyptus plants. However, new evaluations should be performed to monitor the growth and development of the plants until the end of their cycle so as to elucidate the drift effects on the final production.

Intoxicação de eucalipto submetido à deriva simulada de diferentes herbicidas

Besides glyphosate, which is widely utilized, other herbicides such as triclopyr and carfentrazone-ethyl, have a potential use in eucalypt plantations. However, the non-selective nature of these herbicides may lead to plant intoxication due to leaf contact during application. This work aims to evaluate the effects of some herbicides drift on Eucalyptus urophylla, simulated by applying the following subdoses: 0, 43.2, 86.4 and 172.8 g ha-1 of glyphosate; 14.4, 28.8 and 57.6 g ha-1 of triclopyr; 0.84, 1.68 and 3.36 g ha-1 of carfentrazone-ethyl; and the following mixtures: 43.2 g ha-1 of glyphosate + 14.4 g ha-1 of triclopyr; 86.4 g ha-1 of glyphosate + 28.6 g ha1 of triclopyr; 43.2 g ha-1 of glyphosate + 1.68 g ha-1 of carfentrazone-ethyl; and 86.4 g ha1 of glyphosate + 3.36 g ha-1 of carfentrazone-ethyl. The seedlings, about 50 cm high, were applied the herbicides in such a way that their superior third was not reached 45 days after transference. Glyphosate drift caused the most damage to the plant, followed by carfentrazone-ethyl and triclopyr, respectively. Eucalypt plants exposed to a subdose of 172.8 g ha-1 of glyphosate and to glyphosate + carfentrazone-ethyl mixtures, had the highest percentage of intoxication and the lowest growth during the evaluation periods. The plants exposed to triclopyr drift presenting 56.25 and 15.10% of intoxication at 15 and 30 days after application, respectively, were recovered, indicating a lesser triclopyr drift risk, compared with the other herbicides and mixtures studied.

Misturas de herbicidas no manejo de plantas daninhas na cultura do feijão

Avaliou-se a eficacia da combinacao dos herbicidas fomesafen, fluazifop-p-butil e bentazon no manejo integrado de plantas daninhas do feijoeiro (plantio direto e convencional), cultivados em areas anteriormente com milho para grao e silagem. Foi avaliado tambem o residuo do fomesafen no solo aos 125 dias apos a aplicacao (DAA). No plantio convencional, Cyperus rotundus foi a especie dominante, enquanto no plantio direto a infestacao dessa especie foi muito baixa. Nenhuma das combinacoes de herbicidas foi eficiente no controle de C. rotundus. Com excecao de fluazifop-p-butil + bentazon (125 + 480 g ha-1), todas as combinacoes foram eficientes no controle das especies daninhas dicotiledoneas. Nao houve efeito dos tratamentos de herbicidas na produtividade do feijoeiro. O fomesafen, aplicado no plantio direto, causou toxicidade no feijao a partir da dose de 100 g ha-1, sobretudo no milho para silagem. No plantio convencional, sintomas mais leves somente foram observados na dose de 200 g ha-1. Houve residuo de fomesafen no solo apenas na area de plantio direto onde nao havia palhada sobre a superficie do solo, ou seja, na area anteriormente cultivada com milho para silagem. E possivel reduzir doses do fomesafen quando misturado ao bentazon sem afetar a produtividade do feijoeiro. Em areas de feijao cultivado apos colheita do milho para silagem e importante o uso de doses pequenas do fomesafen, para evitar toxicidade a culturas sensiveis subsequentes.

Anatomical characterization of the leaf, stem and rhizome of Digitaria insularis

RESUMO - A anatomia da folha, de colmo e do rizoma de Digitaria insularis foi investigada,visando identificar caracteristicas que possam estar relacionadas a sua tolerância aoglyphosate. Sementes e rizomas de plantas adultas foram coletadas em campo, em area deplantio direto, onde o herbicida glyphosate vem sendo utilizado repetidamente ha variosanos. As plantas provenientes dessas sementes e desses rizomas foram cultivadas emvasos com capacidade de 3 L, contendo solo de textura media, em casa de vegetacao. Quan-do as plantas atingiram o estadio fenologico de pre-florescimento, foram coletadas tresfolhas totalmente expandidas por planta, entre o terceiro e o quinto no. Simultaneamente,coletaram-se fragmentos dos rizomas e os entrenos recobertos pelas bainhas das folhasamostradas. As amostras foram fixadas em FAA

Population dynamics of weeds in no-tillage and conventional crop systems

Abstract Population dynamics of weeds in successive maize and bean crops were evaluated in two soil management systems (conventional and no-tillage), for two maize applications (grain and silage), and in four consecutive growing seasons. Every year, conventional tillage consisted in plowing and harrowing before sowing. In no-tillage, chemical weed desiccation was made with the mixture glyphosate+2.4-D. To control weeds, the mixture fluazifop-p-butil+fomesafen was applied on the bean crop in all the planting seasons, and the herbicides nicosulfuron+atrazine on maize after crop emergence (1998–1999, 1999–2000, 2001–2002) and atrazine+metolachlor before emergence (2000–2001). Purple nutsedge (Cyperus rotundus) was the most important species under conventional soil tillage; while in no-tillage the dicotyledonous weed species (Amaranthus deflexus, Bidens pilosa, Euphorbia heterophylla, Galinsoga parviflora Ipomoea grandifolia) were the most relevant. Regardless of the maize use, the C. rotundus population and tuber bank, with prevailingly dormant tubers, was considerably reduced in no-tillage compared with the conventional system.

Eficiência do triclopyr no controle de plantas daninhas em gramado (Paspalum notatum)

Weeds interfere in the formation, quality and aesthetics of the lawn. Desmodium incanum, and Zornia latifolia, when left uncontrolled, can reach infestation levels that would kill the lawn. Herbicide application is one of the most effective ways of handling weeds in lawn; however, information on the use of these products in lawns is scarce. The objective of this work was to evaluate the efficiency of the herbicide triclopyr in controlling Desmodium incanum and Zornia latifolia in the lawn Bahiagrass (Paspalum notatum). The experiment was developed in a lawn area of the campus of the Federal University of Vicosa, in Vicosa-MG, Brazil, from April to May 2000. The treatments were six doses of triclopyr (0.00; 0.24; 0.48; 0.72; 0.96 and 1.20 kg ha-1) and one dose of the 2,4-D + picloram (0.48 + 0.128 kg ha-1), arranged in a randomized complete block design, with four repetitions. The size of each plot was 12 m² (4.0 x 3.0 m), with the treatments applied in a 2.0 m wide strip, with 1.0 m as lateral check to aid in the visual evaluations. Phytotoxicity evaluations were accomplished at 10 and 20 DAT (days after treatment) and the control level at 15 and 30 DAT, both based on the lateral chek. None of the treatments studied showed damage to the quality of the lawn. Starting with doses of 0.48 and 0.66 triclopyr kg ha-1, controls similar or superior to 90% of Desmodium incanum and Zornia latifolia were obtained, respectively. These results were similar to that of the standard treatment (2,4-D + picloram for 0.48 + 0.128 kg ha-1). It was concluded that triclopyr is a selective herbicide for Bahiagrass, providing excellent control of the weeds studied.