Décio Karam

Efeito de doses reduzidas de glyphosate e paraquat simulando deriva na cultura do sorgo

A aplicacao de herbicidas, seja para dessecacao de culturas ou para controle de plantas daninhas, vem crescendo, devido a expansao da fronteira agricola brasileira. Esse fato aumenta os riscos de ocorrencia de deriva acidental em culturas vizinhas suscetiveis; no entanto, as perdas em produtividade dessas culturas sao desconhecidas em muitas situacoes de ocorrencia de deriva de herbicidas. O objetivo deste trabalho foi avaliar a fitotoxicidade causada por doses reduzidas dos herbicidas glyphosate e paraquat simulando deriva, bem como seus efeitos, no desenvolvimento das plantas e no rendimento de graos de sorgo. O estudo foi conduzido durante os anos agricolas 1996/97 e 1997/98, utilizando-se o hibrido BR 700 no delineamento de blocos ao acaso, com 12 tratamentos e quatro repeticoes. Foram utilizadas cinco doses reduzidas simulando deriva - 2, 4, 6, 8 e 12% da dose recomendada (dose recomendada: 1.440 g ha-1 de glyphosate e 400 g ha-1 de paraquat) - e duas testemunhas sem aplicacao de herbicidas para comparacao. Area foliar e peso da materia seca nao foram afetados pelos tratamentos de deriva, ao passo que a altura da planta foi reduzida sobretudo nas maiores doses dos herbicidas. O teor de clorofila foi afetado apenas no ano agricola 1997/98, ocorrendo maior porcentagem de injurias a medida que se aumentou a concentracao de deriva. No ano agricola 1996/97, os danos observados na parte aerea foram maiores e o estande final chegou a ser reduzido pela maior dose de glyphosate. Com relacao a produtividade, somente no ano agricola 1996/97 houve reducao devido a deriva, em que a maior concentracao de glyphosate resultou em menor peso de paniculas e de graos. No ano agricola 1997/98, nao houve efeito de deriva nas caracteristicas de producao, em razao, provavelmente, da influencia de fatores climaticos. O sorgo e uma planta sensivel a acao de herbicidas nao-seletivos; doses reduzidas, tanto de glyphosate como de paraquat, correspondentes a 12% ou menos da dose recomendada, podem influir no desenvolvimento das plantas, comprometendo a produtividade de graos, sobretudo quando as condicoes climaticas sao favoraveis a acao desses herbicidas.

Genetic diversity among proso millet (Panicum miliaceum) biotypes assessed by AFLP technique

A tecnica de AFLP (Amplified Fragment Length Polymorphism) foi empregada para acessar a diversidade genetica entre tres biotipos domesticados e nove biotipos selvagens de proso millet dos Estados Unidos e do Canada. Oito combinacoes de primers detectaram 39 fragmentos polimorficos de DNA, e a estimativa da distância genetica entre os biotipos variou de 0,02 a 0,04. Colorado-Weld County de sementes pretas e Wyoming-Platte County foram os biotipos mais distintos de acordo com o indice de dissimilaridade. A analise de cluster por UPGMA revelou dois grupos distintos de proso millet mas sem nenhuma relacao geografica. Seis biotipos selvagens que exibiam algumas caracteristicas de plantas cultivadas foram agrupados juntamente com os biotipos domesticados de proso millet, enquanto os tres fenotipos tipicamente selvagens formaram outro grupo distinto por marcadores AFLP.

Mixed field plantation of native and exotic species in semi-arid Brazil

An afforestation of mixed plantation was proposed to provide wood supply and minimise exploratory actions in a biological reserve. Eucalyptus plants were indicated for this purpose. This study was carried out to test the effect of volatile oils extracted from the leaves of Eucalyptus camaldulensis Dehn. and E. grandis Hill ex Maiden on the growth of Enterolobium contortisiliquum (Vell.) Morong. Under laboratory conditions, the Enterolobium plants showed tolerance to E. grandis oil, whereas E. camaldulensis oil caused loss of leaves, inhibition of height and diameter growth and a concomitant decrease in effective PSII quantum yield and the reduction of photosynthetic electron-transport chains. The field growth of E. contortisiliquum was not modified by intercropped E. grandis plants, confirming its tolerance. Inoculation with rhizobia and or mycorrhizal fungi significantly improved the height and diameter growth of these species. The results showed that E. contortisiliquum plants could be intercropped with E. grandis for reforestation and agroforestry systems.

Seletividade de herbicidas sobre Myracrodruon urundeuva (Aroeira)

The objective of this work was to verify the selectivity of herbicides applied in eucalyptus areas upon the growth of Myracrodruon urundeuva.. The experiment was carried out under greenhouse conditions during two seasons (2002 and 2003), in a completely randomized experimental design with five herbicides in four doses arranged in a factorial design 5x4, and six replicates. The treatments were: haloxyfop-methyl at the doses (0.00, 120, 240 and 480 g ha-1); sulfentrazone (0.00, 300, 600 and 1.200 g ha-1), isoxaflutole (0.00, 150, 300 and 600 g ha-1); oxyfluoren (0.00, 720, 1.440 and 2.880 g ha-1) and glyphosate (0.00, 720, 1.440 and 2.880 g ha-1) plant toxicity effects, number of leaflets and plant height were evaluated in both experiments and analyses of chlorophyll a and b and carotenoids were also conducted in the second. Glyphosate presented the highest plant toxicity, compromising the development of the aroeira plant, thus it is not recommended for weed control in aroeira planting areas. The other herbicides did not compromise the development of this plant, thus they can be potentially used in weed management control of this species.

Capim-colonião e seus efeitos sobre o crescimento inicial de clones de Eucalyptus × urograndis

This study aimed to evaluate the guinea grass effect ( Panicum maximum ) on the initial growth of different Eucalyptus x urograndis clones. Two assays were established with eucalyptus clones and guinea grass seedlings. The plants were grown in plots with cement borders filled with soil. Each plot received a eucalyptus seedling. The first assay had a completely randomized experimental design, with three replications, and treatments in a 5x2 factorial scheme (five eucalyptus clones and the absence or presence of two guinea grass plants at 10 cm distance from eucalyptus seedling). The second assay was similar to the first, however with three eucalyptus clones. The experimental design was completely randomized, with five replications, and a 3x2 factorial scheme (three eucalyptus clones and the absence or presence of two guinea grass plants). The presence of eucalyptus clones did not affect guinea grass development. The eucalyptus clones that coexisted with guinea grass plants did not show differences in their development, making the clones equal when under competition. The most susceptible characteristics of eucalyptus clones to guinea grass were foliar area, shoot and stem dry matter. Clone 3 showed the most sensitivity to guinea grass, and clone 1 was the most tolerant, but all clones studied suffered a negative interference from guinea grass.

Mathematical and biological analysis of the models for estimating culture yield losses due to weed interference

The presence of weeds in any production system involving plants causes crop yield losses. Mathematical models for crop yield loss estimation due to the interference of weeds can be useful tools for decision-making management strategies. If it is possible to predict crop yield loss, it will be possible to decide whether it is viable to apply control measures. There are several empirical models in the literature used to estimate crop yield loss due to the presence of weeds, which are linear, non linear and polynomial. The goal of this work is to present an analysis of the existing mathematical models used to estimate crop yield loss due to weeds by considering both their mathematical fit and biological behavior.

Revisão de modelos matemáticos da dinâmica do banco de sementes de plantas daninhas em agrossistemas

O crescimento das plantas obedece a certos principios fisiologicos, que podem ser descritos em termos quantitativos, ate certo ponto, por equacoes matematicas. No ambiente agricola, a dinâmica do banco de sementes esta fortemente relacionada ao estabelecimento de especies daninhas e pode ser descrita por um sistema de equacoes que relaciona a densidade de plântulas com a densidade de sementes produzidas em areas de cultivo. O objetivo deste artigo foi descrever, atraves de modelos matematicos citados na literatura, as caracteristicas do comportamento dinâmico do banco de sementes de populacoes de plantas daninhas em sistemas agricolas.

Interferência de plantas daninhas na cultura do sorgo sacarino

This work aimed to carry out a phytosociological study and to determine the critical period of weed interference on sweet sorghum crop. The experimental design adopted was randomized blocks with three replications. Treatments consisted by increasing periods of control or coexistence of weeds in different phenological stages of crop growth: 0-3 (V3), 0-5 (V5), 0-7 (V7), 0-9 (V9), 0-11(V11) fully expanded leaves and 0-R5 (harvest). The weed community was evaluated based on number the number of individuals and their correspondent dry mass accumulation, for each weed population in different periods of coexistence. Sweet sorghum was harvested at 101 days after emergence, when was measured plant height, culm diameter, total soluble solids (°Brix) in function of coexistence periods between crop and weeds, besides the yield of culms. Commelina benghalensis e Panicum maximum were the two species of higher relative importance at the crop harvested. The lack of weed control, during the crop cycle, caused an increase in total soluble solids (°Brix) and reduction of, respectively, 9 and 25% in plant height and culms diameter when compared with the hoed control during all cycle. Accepting losses of 5% in culm yield, was observed that the critical period of weed interference corresponded to the period of time between the phenological growth stage V3 to V11.

Potential of macrophytes for removing atrazine from aqueous solution

The potential of three macrophytes, Azolla caroliniana, Salvinia minima, and Lemna gibba was assessed in this study to select plants for use in environmental remediation contaminated with atrazine. Experiments were carried out in a greenhouse over six days in pots containing Hoagland 0.25 strength nutritive solution at the following atrazine concentrations: 0; 0.01; 0.1; 1.0; 10.0 mg L-1. Decrease in biomass accumulation was observed in the three macrophytes, as well as toxic effects evidenced by the symptomatology developed by the plants which caused their deaths. The chlorosis and necrosis allowed to observe in the plants the high sensitivity of the three species to the herbicide. Plants presented low potential for removal of atrazine in solution when exposed to low concentrations of the herbicide. However, at the 10.0 mg L-1 atrazine concentration, L. gibba and A. caroliniana showed potential to remove the herbicide from the solution (0.016 and 0.018 mg atrazine per fresh mass gram, respectively). This fact likely resulted from the processes of atrazine adsorption by the dead material. The percentage of atrazine removed from the solution by the plants decreased when the plants were exposed to high concentrations of the pollutant. Azolla caroliniana, S. minima, and L. gibba were not effective in removing the herbicide from solution. The use of these species to remedy aquatic environments was shown to be limited.

Sistema de classificação fuzzy para o risco de infestação por plantas daninhas considerando a sua variabilidade espacial

Este artigo trata do problema de classificacao do risco de infestacao por plantas daninhas usando tecnicas geoestatisticas, analise de imagens e modelos de classificacao fuzzy. Os principais atributos utilizados para descrever a infestacao incluem a densidade de sementes, bem como a sua extensao, a cobertura foliar e a agressividade das plantas daninhas em cada regiao. A densidade de sementes reflete a producao de sementes por unidade de area, e a sua extensao, a influencia das sementes vizinhas; a cobertura foliar indica a extensao dos agrupamentos das plantas daninhas emergentes; e a agressividade descreve a porcentagem de ocupacao de especies com alta capacidade de producao de sementes. Os dados da densidade de sementes, da cobertura foliar e da agressividade para as diferentes regioes sao obtidos a partir de simulacao com modelos matematicos de populacoes. Neste artigo propoe-se um sistema de classificacao fuzzy utilizando os atributos descritos para inferir os riscos de infestacao de regioes da cultura por plantas daninhas. Resultados de simulacao sao apresentados para ilustrar o uso desse sistema na aplicacao localizada de herbicida.