-The use of herbicides, even in tolerant crops, can cause stress evidenced by increase phytotoxicity affecting growth and development. The objectives of this study were to evaluate herbicides effect from different mechanisms of action in photosynthetic and oxidative stress parameters, as well visual phytotoxicity and wild radish control in wheat crop, cultivar Quartzo. Two trials were conducted where the first one evaluated the photosynthetic parameters on wheat plants in two seasons collection, following the application of herbicides bentazon, clodinafop, iodosulfuron, metribuzin, metsulfuron and 2,4-D; and the second one evaluated wild radish (Raphanus sativus) control, wheat phytotoxicity and yield due to bentazon, iodosulfuron, metribuzin, metsulfuron and 2,4-D herbicides application. Photosynthetic rate, stomatal conductance and transpiration were negatively affected by metribuzin, metsulfuron and 2,4-D herbicides at 24 and 120 HAS (hours after spraying) compared to control. Oxidative stress was similar or lower to control, when herbicide was applied and, in general, there was no difference between application times. Lipid peroxidation, catalase activity and phenols were higher in the first collection time. The application of herbicides iodosulfuron and 2,4-D reduces chlorophylls and carotenoids in wheat. Herbicides bentazon, iodosulfuron, metribuzin, metsulfuron and 2,4-D are selective to wheat, cultivar Quartzo and do not affect wheat yield. 2,4-D, metribuzin and iodosulfuron are more efficient for wild radish control. Keywords
Yellow nutsedge (Cyperus esculentus) is adapted to flooding and reduces yield in irrigated rice. Information on the competitive ability of this weed with the crop and the size of the economic damage caused is lacking. Mathematical models quantify the damage to crops and support control decision-making. This study aimed to determine yield losses and economic thresholds (ET) of this weed in the culture according to weed population and time of onset of irrigation of the crop. The field study was conducted in the agricultural year of 2010/2011 in Pelotas/RS to evaluate the competitive ability of BRS Querência in competition with different population levels of yellow nutsedge and two periods of onset of flood irrigation (14 and 21 days after emergence). The hyperbolic model satisfactorily estimated yield losses caused by yellow nutsedge. Population of yellow nutsedge was the variable most fitted to the model. The delay of seven days for the beginning of rice irrigation causes decrease in competitive ability of BRS Querência, and based on the ET calculated to the price paid for rice, it is necessary between two and thirteen plants m -2 weed to justify the control in the first and second period of irrigation, respectively. Increases in yield, price paid for rice and control efficiency of the herbicide, besides reduction of costs of controlling promote reduction of ET of yellow nutsedge in rice crops, justifying the adoption of control measures even at smaller weed population.Key words: Cyperus esculentus, Oryza sativa, rectangular hyperbole.Perdas de produtividade e níveis de dano econômico de tiririca-amarela em arroz irrigado em função do início da irrigação por inundação Resumo A tiririca-amarela (Cyperus esculentus) é adaptada ao alagamento e causa redução de produtividade do arroz irrigado. Informações da habilidade competitiva da planta daninha com a cultura e a dimensão do prejuízo econômico por ela causado são escassas. Modelos matemáticos quantificam prejuízos às culturas e subsidiam a tomada de decisão de controle. O objetivo deste estudo foi determinar perdas de produtividade e níveis de dano econômico (NDE) da tiririca-amarela na cultura em função da população da planta daninha e da época de início da irrigação da cultura. Foi conduzido estudo a campo, na safra 2010/2011, no município de Pelotas, RS, para avaliar a habilidade competitiva da cultivar de arroz BRS Querência em competição com diferentes níveis populacionais de tiririca-amarela em duas épocas de início de irrigação da cultura (14 e 21 dias após a emergência). O modelo hiperbólico estimou satisfatoriamente as perdas de produtividade que a tiririca-amarela causa à cultura. A variável mais ajustada ao modelo foi a população de tiririca-amarela. O atraso de sete dias no início da irrigação do arroz causa decréscimo na habilidade competitiva da cultivar BRS Querência, sendo necessárias, com base nos NDE calculados à variável preço pago pelo arroz, entre duas e 13 plantas m -2 da planta daninha para justificar o controle na primeira e segunda...
-Determining the periods of weed competition with crops helps the producer to choose the most appropriate time to use weed control practices. This strategy allows for the reduction of the number of herbicide applications, reducing costs and the environmental impact of pesticides. The objectives were to determine the period before the interference (PBI) of crabgrass (Digitaria ciliaris) competing with flooded rice, the critical period of interference prevention (CPIP) of crabgrass with soybean and the effects of competition on the grains yield and their components. Experiments were conducted with the coexistence of BRS Querência rice cultivar with crabgrass, for periods of 0, 7, 14, 21, 28, 35, and 110 days after emergency (DAE) and Fundacep 53RR soybean cultivar, whose periods of coexistence and control of crabgrass were 0, 7, 14, 21, 28, 35, and 156 DAE. Rice can grow with crabgrass infestation until 18 DAE, while soybean should remain free from the presence of crabgrass in the period between 23 and 50 DAE. The grain yield and its components, in the crops studied, are affected when grown with crabgrass. BRS Querência, com milhã, por períodos iniciais crescentes de 0, 7, 14, 21, 28, 35 Keywords: Digitaria ciliaris, Oryza sativa, Glycine max, interference RESUMO -A determinação dos períodos de competição das plantas daninhas com as culturas auxilia o produtor na escolha do momento mais adequado para utilizar medidas de manejo. Essa estratégia possibilita reduzir o número de aplicações de herbicidas, com consequente redução de custo e menor impacto dos agrotóxicos ao ambiente. Assim, os objetivos deste trabalho foram determinar o período anterior à interferência (PAI) de milhã (Digitaria ciliaris) na cultura do arroz irrigado, o período crítico de prevenção à interferência (PCPI) de milhã na cultura da soja e os efeitos da competição na produtividade de grãos e seus componentes. Para isso, foram conduzidos experimentos de convivência de arroz irrigado, cultivar
The goals of this study were to evaluate herbicide application rates at different timings for preharvest desiccation of wheat (Trial 1), as well as to evaluate the effect of the timing of herbicide desiccation at preharvest and harvest timing (Trial 2) on yield, germination, and herbicide residue in wheat seed. In Trial 1, treatments consisted of two application rates of glufosinate, glyphosate, paraquat, or paraquat+diuron and a control without application; application time periods were in the milk grain to early dough stage, soft dough to hard dough stage, and hard dough stage. In Trial 2, treatments consisted of different application time periods (milk grain to early dough stage, and soft dough to hard dough stage), different herbicides (glufosinate, 2,4-D+glyphosate, and untreated control), and different harvest times (5, 10 and 15 days after herbicide application). One thousand seeds weight, yield, first and final germination count, and herbicide residue on seeds were evaluated. Preharvest desiccation with paraquat, glufosinate, and 2,4-D+glyphosate at the milk grain to early dough stage reduces wheat yield. Regardless of the herbicide and application rate, application in the milk grain to early dough stage and soft dough to hard dough stage provides greater germination of wheat seeds, except at the lower dose of paraquat. Systemic herbicides accumulate more in wheat seeds.
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