As all herbicides act on pathways or processes crucial to plants, in an inhibitory or stimulatory way, low doses of any herbicide might be used to beneficially modulate plant growth, development, or composition. Glyphosate, the most used herbicide in the world, is widely applied at low rates to ripen sugarcane. Low rates of glyphosate also can stimulate plant growth (this effect is called hormesis). When applied at recommended rates for weed control, glyphosate can inhibit rust diseases in glyphosate-resistant wheat and soybean. Fluridone blocks carotenoid biosynthesis by inhibition of phytoene desaturase and is effective in reducing the production of abscisic acid in drought-stressed plants. Among the acetolactate synthase inhibitors, sulfometuron-methyl is widely used to ripen sugarcane and imidazolinones can be used to suppress turf species growth. The application of protoporphyrinogen oxidase inhibitors can trigger plant defenses against pathogens. Glufosinate, a glutamine synthetase inhibitor, is also known to improve the control of plant diseases. Auxin agonists (i.e., dicamba and 2,4-D) are effective, low-cost plant growth regulators. Currently, auxin agonists are still used in tissue cultures to induce somatic embryogenesis and to control fruit ripening, to reduce drop of fruits, to enlarge fruit size, or to extend the harvest period in citrus orchards. At low doses, triazine herbicides stimulate growth through beneficial effects on nitrogen metabolism and through auxin-like effects. Thus, sublethal doses of several herbicides have applications other than weed control.
Amicarbazone is a new triazolinone herbicide with a broad spectrum of weed control. The phenotypic responses of sensitive plants exposed to amicarbazone include chlorosis, stunted growth, tissue necrosis, and death. Its efficacy as both a foliar- and root-applied herbicide suggests that absorption and translocation of this compound is very rapid. This new herbicide is a potent inhibitor of photosynthetic electron transport, inducing chlorophyll fluorescence and interrupting oxygen evolution ostensibly via binding to the QB domain of photosystem II (PSII) in a manner similar to the triazines and the triazinones classes of herbicides. As a result, its efficacy is susceptible to the most common form of resistance to PSII inhibitors. Nonetheless, amicarbazone has a good selectivity profile and is a more potent herbicide than atrazine, which enables its use at lower rates than those of traditional photosynthetic inhibitors.
RESUMO -Este trabalho é parte integrante de um projeto de pesquisa que tem por objetivo o desenvolvimento de programas de manejo integrado de plantas aquáticas em cinco reservatórios da bacia do rio Tietê, usados na produção de energia elétrica. A ocorrência de plantas aquáticas foi correlacionada com a qualidade da água e do sedimento. Amostragens de água e sedimento e levantamento de plantas foram realizados em junho de 2001 (estação seca), outubro/novembro de 2001 (início da estação chuvosa) e fevereiro/março de 2002 (final da estação chuvosa). Amostras de água foram utilizadas para estimar a transmissão ou extinção de luz em comprimentos de onda de 190 a 900 nm para colunas de água de 1 m de profundidade. Para melhor entendimento e registro (em fotos digitais) dos problemas com formação de bancos de sedimento e plantas aquáticas, todos os reservatórios foram sobrevoados, usando um helicóptero, nos dias 4 e 5 de junho de 2001. Os resultados permitiram concluir que a ocorrência de plantas submersas, destacando-se Egeria densa e Egeria najas, foi a mais dependente da transparência da água e transmissão de luz. A maior turbidez e sólidos suspensos contidos e a menor transmissão de luz alteram a freqüência de plantas submersas. Os reservatórios de Promissão e Nova Avanhandava foram os mais infestados com plantas submersas. A ocorrência de plantas marginais e flutuantes é muito dependente da formação de bancos de sedimentos. Os reservatórios de Barra Bonita, Bariri e Ibitinga foram os mais infestados com plantas marginais e flutuantes. A concentração de fósforo e nitrogênio, a turbidez e os sólidos suspensos foram reduzidos com o deslocamento ao longo da seqüência de reservatórios no rio Tietê (Barra Bonita => Bariri => Ibitinga => Promissão => Nova Avanhandava).Palavras-chave: qualidade de água, planta aquática, sedimento, reservatório. (São Paulo, Brasil) ABSTRACT -This research is part of a project aiming to develop aquatic plant integrated management programs in five reservoirs of the Tietê watershed
The sulfentrazone is regularly applied to sugarcane crop harvest residue for PRE control of weedy species, especially in the dry season during the year, but little is known about how rainfall timing or crop residue mass affect the release of sulfentrazone into the soil and its subsequent effectiveness. Two experiments were conducted to examine the effects of sugarcane residue mass (5, 10, 15, and 20 t ha−1) and rainfall timing (1, 30, and 60 d after herbicide application) on sulfentrazone retention. Rainfall volumes were simulated at 2.5, 5, 10, 20, 35, 50, and 100 mm. A 20-mm rainfall volume was simulated at 7 and 14 d after the first simulated event. The water passing through the straw was collected after each rainfall simulation. The concentration of sulfentrazone was measured by liquid chromatography and mass spectrometry. The initial 20 mm of rain released the maximum mass of sulfentrazone from the sugarcane residue. The mass of sugarcane residue affected the amount of sulfentrazone recovered. The amount of sulfentrazone released from the residue was significantly reduced by the persistence on the residue surface for long periods before the occurrence of rain. During periods of low rainfall, recommendations for sulfentrazone rate must take into account losses that occur when applied over the harvest residues to design a weed-management plan that does not compromise efficacy and duration of the residual effects.
-This study has aimed to develop a method for simultaneous extraction and determination by liquid chromatography and mass spectrometry (LC-MS/MS) of glyphosate, aminomethylphosphonic acid (AMPA), shikimic acid, quinic acid, phenylalanine, tyrosine and tryptophan. For the joint analysis of these compounds the best conditions of ionization in mass spectrometry and for chromatographic separation of the compounds were selected. Calibration curves and linearity ranges were also determined for each compound. Different extraction systems of the compounds were tested from plant tissues collected from sugarcane (Saccharum officinarum) and eucalyptus (Eucalyptus urophylla platiphylla) plants two days after the glyphosate application at the dose of 720 g a.e. ha -1 . The plant material was dried in a forced air circulation drying oven and in a lyophilizer, and subsequently the extractions with acidified water (pH 2.5), acetonitrile-water (50:50) [v/v] and methanol-water (50:50) [v/v] were tested. To verify the recovery of the compounds in the plant matrix with acidified water as an extracting solution, the samples were fortified with a solution containing the mixture of the different analytical standards present so that this one presented the same levels of 50 and 100 μg L -1 of each compound. All experiments were conducted with three replicates. The analytical method developed was efficient for compounds quantifications. The extraction from the samples dried in an oven and using acidified water allowed better extraction levels for all compounds. The recovery levels of the compounds in the fortified samples with known amounts of each compound for both plants samples were rather satisfactory.Keywords: herbicide, LC-MS/MS, metabolites, metabolic profile. (pH 2,5), acetonitrila-água (50:50) [v/v] e metanol-água (50:50) [v/v] RESUMO -Este trabalho teve como objetivo o desenvolvimento de um método de extração e determinação simultânea por cromatografia líquida e espectrometria de massas (LC-MS/MS) de glyphosate, ácido aminometilfosfônico (AMPA), ácido chiquímico, ácido quínico, fenilalanina, tirosina e triptofano. Para a análise conjunta desses compostos, foram selecionadas as melhores condições de ionização no espectrômetro de massas e para a separação cromatográfica dos compostos. Também foram determinadas as curvas de calibração e faixas de linearidade para cada um dos compostos. Foram testados diferentes sistemas de extração dos compostos a partir de tecidos vegetais coletados de planta de cana-de-açúcar (Saccharum officinarum) e eucalipto (Eucalyptus
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