Efeito do glyphosate em plantas daninhas da família poaceae submetidas a diferentes potenciais hídricos do solo
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2018-02-02
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Universidade Estadual Paulista (Unesp)
Resumo
A ação de herbicidas sobre plantas daninhas que se desenvolvem sob déficit hídrico pode ser comprometida, pois as rotas de penetração de herbicidas como o glyphosate são reduzidas em razão da menor hidratação da cutícula nessas plantas. Avaliou-se nesse estudo a eficiência de controle do herbicida glyphosate em quatro espécies de plantas da família Poaceae quando submetidas a distintos déficits hídricos. Os estudos foram conduzidos em casa-de-vegetação sendo que as espécies estudadas foram: capim-colonião (Megathyrsus maximum), capim-colchão (Digitaria nuda), capim-massambará (Sorghum halepense) e capim-braquiária (Urochloa ruziziensis). As plantas foram submetidas a três condições hídricas do solo [sem restrição hídrica (-0,03 MPa), déficit hídrico intermediário (-0,07 MPa) e alta restrição hídrica (-1,5 MPa)], aplicou-se três doses do herbicida glyphosate (0,0; 270,0 e 540,0 g e.a. ha-1) e em dois estádios fenológicos de desenvolvimento da planta (4-6 folhas e 1-3 perfilhos). O manejo hídrico teve início quando as plantas apresentaram duas folhas desenvolvidas. Foram realizadas avaliações visuais de controle aos 7, 14, 21 e 35 dias após a aplicação do herbicida; analisou-se ainda os parâmetros morfofisiológicos área foliar específica, condutância estomática e a diferença de temperatura do ambiente com a temperatura foliar no dia da aplicação do herbicida, bem como a matéria seca da parte aérea e da raiz ao final do estudo. Os resultados obtidos de controle e matéria seca foram submetidos à análise de variância pelo teste “F” e as médias foram comparadas pelo teste “t” de Student (p>0,05). Os parâmetros morfofisiológicos foram analisados através do intervalo de confiança a um coeficiente de confiança de 95%. Com o aumento da restrição hídrica, houve diminuição dos componentes morfofisiológicos da planta de capim-colonião, capim-colchão, capim-massambará e capim-braquiária como área foliar específica, condutância estomática, e a diferença entre a temperatura ambiente e foliar. O controle das plantas de capim-colonião foi mais eficiente quando ocorreu a aplicação da dose de 540 g ha-1 de glyphosate no estádio vegetativo de 1-3 perfilhos, no manejo hídrico de -0,03 MPa. Plantas de capim-colchão foram totalmente controladas a partir dos 21 DAA, independente do manejo ao qual a planta foi submetida e a dose utilizada para seu controle. Isso evidencia que esta planta é muito sensível ao herbicida glyphosate, e ao déficit hídrico, podendo realizar seu controle com doses mais reduzidas na época seca. Já para o controle do capim-massambará, as plantas foram totalmente controladas quando houve a aplicação de 540 g ha-1 de glyphosate e quando a aplicação ocorreu no estádio vegetativo de 4-6 folhas, nos manejos hídricos de -0,03 e -0,07 MPa. Plantas que desenvolveram sob restrição hídrica severa (-1,5 MPa), o controle não foi eficiente. O controle do capim-braquiária foi eficiente com a utilização de 540 g ha-1 de glyphosate quando as plantas não desenvolveram em condições de déficit hídrico, tanto nos estádios iniciais de desenvolvimento quanto no estádio mais tardio. A mesma dose foi eficiente no controle de plantas mantidas a um manejo hídrico de -0,07 MPa de umidade do solo, quando controladas no estádio de 4-6 folhas. A redução da dose de glyphosate para 270 g ha-1 não foi eficiente para controlar o capim-braquiária, principalmente em plantas sem restrição hídrica na qual houve rebrota. As plantas pulverizadas com glyphosate tem seu controle comprometido quando as mesmas foram submetidas a déficit hídrico.
The action of herbicides on weeds that develop under water deficit can be compromised, the penetration routes of glyphosate herbicide are reduced due to the less hydration of the cuticle in these plants. The control efficiency of glyphosate herbicide in four species of plants of the Poaceae when submitted to different water deficits was evaluated in this study. The studies were carried out in a greenhouse and the species studied were: guineagrass (Megathyrsus maximum), naked crabgrass (Digitaria nuda), johngrass (Sorghum halepense) and congograss (Urochloa ruziziensis). In the treatments, the plants were submitted to three soil water conditions (no water deficit (-0.03 MPa), intermediate water deficit (-0.07 MPa) and high water restriction (-1.5 MPa)), three doses of glyphosate herbicide, (0.0, 270.0 and 540.0 g e.a. ha-1) and two phenological stages of plant development (4-6 leaves and 1-3 tillers). Water management started when the plants had two leaves developed. Visual evaluations were carried out at 7, 14, 21 and 35 days after application of the herbicide; the specific leaf area, stomatal conductance and the temperature difference of the environment with the leaf temperature on the day of application of the herbicide, as well as the dry matter of the aerial part and of the root were analyzed at the end of the study. The results of control and dry matter were submitted to analysis of variance by the "F" test and the means were compared by the Student “t” test (p> 0.05). The morphophysiological parameters were analyzed through the confidence interval at a confidence coefficient of 95%. With the increase of water restriction, there was a decrease in the morphophysiological components of the guineagrass, naked crabgrass and johngrass as a specific leaf area, stomatal conductance, and the difference between ambient and leaf temperature. The control of the guineagrass was more efficient when the application of the dose of 540 g ha-1 of glyphosate occurred and when they were controlled in the vegetative stage of 1-3 tillers, in the water management of -0.03 MPa, that is, the plant that develops under water restrictions may have its control affected. Naked crabgrass were fully controlled from 21 DAA, regardless of the management to which the plant was submitted and the dose used for its control. This shows us that this plant is very sensitive to the glyphosate herbicide, and to the water deficit, being able to carry out its control with smaller doses in the dry season. In order to control the johngrass, the plants were totally controlled with the application of 540 g ha-1 of glyphosate and when they were controlled in the vegetative stage of 4-6 leaves, in the water management of -0.03 and -0.07 MPa. Plants that developed under severe water restriction (-1.5 MPa), the control was not efficient. Congograss control was efficient with a use of 540 g ha-1 of glyphosate when developed under water deficit conditions, both in the early stages of development and in the later stages. The same dose was efficient in the control of plants maintained at a -0.07 MPa soil moisture, when controlled at the 4-6 leaf stage. A dose reduction of glyphosate to 270 g ha-1 was not efficient to control congograss, especially in plants no water restriction in which regrowth occurred. Plants sprayed with glyphosate have control compromised when they were submitted to water deficit.
The action of herbicides on weeds that develop under water deficit can be compromised, the penetration routes of glyphosate herbicide are reduced due to the less hydration of the cuticle in these plants. The control efficiency of glyphosate herbicide in four species of plants of the Poaceae when submitted to different water deficits was evaluated in this study. The studies were carried out in a greenhouse and the species studied were: guineagrass (Megathyrsus maximum), naked crabgrass (Digitaria nuda), johngrass (Sorghum halepense) and congograss (Urochloa ruziziensis). In the treatments, the plants were submitted to three soil water conditions (no water deficit (-0.03 MPa), intermediate water deficit (-0.07 MPa) and high water restriction (-1.5 MPa)), three doses of glyphosate herbicide, (0.0, 270.0 and 540.0 g e.a. ha-1) and two phenological stages of plant development (4-6 leaves and 1-3 tillers). Water management started when the plants had two leaves developed. Visual evaluations were carried out at 7, 14, 21 and 35 days after application of the herbicide; the specific leaf area, stomatal conductance and the temperature difference of the environment with the leaf temperature on the day of application of the herbicide, as well as the dry matter of the aerial part and of the root were analyzed at the end of the study. The results of control and dry matter were submitted to analysis of variance by the "F" test and the means were compared by the Student “t” test (p> 0.05). The morphophysiological parameters were analyzed through the confidence interval at a confidence coefficient of 95%. With the increase of water restriction, there was a decrease in the morphophysiological components of the guineagrass, naked crabgrass and johngrass as a specific leaf area, stomatal conductance, and the difference between ambient and leaf temperature. The control of the guineagrass was more efficient when the application of the dose of 540 g ha-1 of glyphosate occurred and when they were controlled in the vegetative stage of 1-3 tillers, in the water management of -0.03 MPa, that is, the plant that develops under water restrictions may have its control affected. Naked crabgrass were fully controlled from 21 DAA, regardless of the management to which the plant was submitted and the dose used for its control. This shows us that this plant is very sensitive to the glyphosate herbicide, and to the water deficit, being able to carry out its control with smaller doses in the dry season. In order to control the johngrass, the plants were totally controlled with the application of 540 g ha-1 of glyphosate and when they were controlled in the vegetative stage of 4-6 leaves, in the water management of -0.03 and -0.07 MPa. Plants that developed under severe water restriction (-1.5 MPa), the control was not efficient. Congograss control was efficient with a use of 540 g ha-1 of glyphosate when developed under water deficit conditions, both in the early stages of development and in the later stages. The same dose was efficient in the control of plants maintained at a -0.07 MPa soil moisture, when controlled at the 4-6 leaf stage. A dose reduction of glyphosate to 270 g ha-1 was not efficient to control congograss, especially in plants no water restriction in which regrowth occurred. Plants sprayed with glyphosate have control compromised when they were submitted to water deficit.
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gramíneas-déficit hídrico, herbicida, monocotiledôneas, controle, grass-water deficit, herbicide, monocot, control