Yield loss and economic thresholds of yellow nutsedge in irrigated rice as a function of the onset of flood irrigation

Abstract

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...

Economic Threshold Levels for Signal Grass Control in Sugarcane Cultivars

“…This parameter allows the comparison of the maximum yield losses among cultivars of a particular crop (Westendorff et al, 2014;Machado et al, 2015). This parameter was lower (76.17) for cultivar SP801816, showing, once again, the least yield loss of this cultivar when in competition with B. brizantha; other cultivars presented similar values for this parameter (Table 1).…”

“…This parameter is used as an index to compare the relative competitiveness among cultivars (Galon and Agostinetto, 2009) (Galon and Agostinetto, 2009). The faster the crop growth and the soil coverage, the higher is the competitive ability with weeds (Westendorff et al, 2014).…”

“…In order to increase yield from 76 to 114 ton ha as competition with weeds (Westendorff et al, 2014;Machado et al, 2015). The low ETL found for sugarcane cultivation is due to the high yield of the crop, in which a yield loss of less than 4% (considering intermediate values) inflicts economic damage that justifies weed control.…”

“…This is the concept of an economic threshold level (ETL), a tool that helps farmers make decisions about weed control (Vidal et al, 2010;Westendorff et al, 2014).…”

“…These practices may favor the development of the crop to the detriment of weed species, thus increasing the population of weed species required to achieve ETL (Galon and Agostinetto, 2009;Westendorff et al, 2014).…”