RESUMO: Euphorbia davidii (Euphorbiaceae) é uma planta infestante de ciclo anual primaveril-estival presente na Província de Buenos Aires, Argentina. O objetivo deste estudo foi comparar a sensibilidade ao glyphosate de diferentes populações de Euphorbia davidii. Para isso, foram usadas duas técnicas: bioensaio com sementes e determinação dos níveis de chiquimato nas plantas tratadas com glyphosate. Fez-se uma comparação da germinação de sementes de populações provenientes de Espartillar, Barrow, Olavarria e Azul, expostas a diferentes concentrações de glyphosate. Procedeu-se à determinação dos níveis de chiquimato em plantas provenientes das mesmas localidades e tratadas com o herbicida. A população mais sensível foi a de Espartillar, com uma CE50 (concentração efetiva média) de 4,00 g a.e. L-1. Com base neste valor, o índice de resistência de cada local de origem foi de 1,76 , 2,39 e 2,48 para Azul, Olavarría e Barrow, respectivamente. Entre as plantas tratadas, em que os valores de chiquimato foram determinados, observou-se apenas aumento significativo na concentração desse metabólito na população de Espartillar. Nas outras populações não foi identificada qualquer acumulação de chiquimato. Os resultados mostram a sensibilidade diferencial ao glyphosate das populações avaliadas.

ABSTRACT: Euphorbia davidii (Euphorbiaceae) is a summer annual weed present in the Province of Buenos Aires, Argentina. The aim of this study was to compare the sensitivity to glyphosate of different populations of Euphorbia davidii. Two techniques were used: a seed bioassay and shikimate determination in glyphosate-treated plants. Germination rates of seeds belonging to the populations from Espartillar, Barrow, Olavarria and Azul exposed to different concentrations of glyphosate were compared. Plants from the same locations treated with glyphosate were evaluated to determine shikimate levels. The most sensitive population was from Espartillar, with a CE50 (average effective concentration) of 4.00 g e.a. L-1. Based on this finding, the resistance index for each population was 1.76, 2.39 and 2.48 for Azul, Olavarria and Barrow respectively. Regarding glyphosate-treated plants in which shikimate levels were determined, a significant increase in the concentration of this metabolite was only observed in the population from Espartillar. Accumulation of shikimate was not detected in the other groups. These results show differential sensitivity to glyphosate of the evaluated populations.

Euphorbia dentata is an annual, spring-summer weed present in 85% of the agricultural land of the District of Azul, province of Buenos Aires, Argentina. Field studies were conducted during two years with the aim of (i) adjusting the dose and time of application that would achieve an efficient control of E. dentata with glyphosate and (ii) studying the use of different concentrations of surfactant to achieve more predictable field results. To address aim (i), a trial consisting in applying increasing doses of the herbicide was carried out in two phenological stages of the weed. Based on the data obtained, rate-response relationships were established, linear regression equations were derived and the glyphosate rate required to achieve 90% control for each phenological stage of the weed was determined. To address aim (ii), a second trial was conducted to determine the influence of adding a surfactant on the interaction between dose and weed stage. Glyphosate control efficacy was found to be dependent on the phenological stage of the weed. Surfactant addition to the aspersion solution improved the overall efficacy of the glyphosate dose applied, with a greater influence being detected in the treatments carried out at more advanced phenological stages tested.

Euphorbia dentata es una maleza anual, de ciclo primaveral estival que está presente en el 85% del área agrícola del partido de Azul, provincia de Buenos Aires, Argentina. Estudios en campo fueron conducidos durante dos años a fin de realizar ajustes de dosis y momentos de aplicación que permitan lograr una alta eficacia de control de E. dentata con glifosato y estudiar el uso de distintas concentraciones de un surfactante, para lograr resultados más predecibles en aplicaciones a campo. Se realizó un ensayo que consistió en la aplicación de dosis crecientes del herbicida en dos estados fenológicos de la maleza y con los datos se establecieron relaciones dosis respuesta, se ajustaron ecuaciones de regresión lineal y se determinaron las dosis de glifosato necesarias para lograr un 90% de control para cada estado fenológico de la maleza. Otro ensayo fue conducido para determinar la influencia del agregado de un surfactante en interacción con la dosis y el estado de la maleza. Se observó una dependencia de la eficacia de control de glifosato respecto del estado fenológico. La adición del surfactante a la solución de aspersión mejoró, en general la eficacia obtenida por las dosis de glifosato, detectándose una mayor influencia en los tratamientos realizados en estados fenológicos avanzados.

Euphorbia dentata is a spring-summer annual weed first detected in Azul Co., Buenos Aires Province, Argentina., in 1983, in an isolated soybean crop spot crops. It is now found as a weed in 85 % of the cropland, with densities ranging from 20 to 200 plants m-2. Two year- field studies were conducted to determine the competition relationship between soybean and E. dentata. The effect of different weed densities was evaluated on yield parameters and biomass. Both soybean dry weight and yield gave a significant response to weed density and biomass, resulting in a reduction of 80% due to interference starting at a density of 20 plants m². It was determined that E. dentata has a strong influence on soybean yield showing a linear response at the range of the studied densities, fitted to a regression equation indicating that seed production decreases 6,73 kg ha-1 for each plant m-2 increase of E. dentata. From the crop yield components, the number of pods per plant was more severely affected by competition reducing yield in 40%, when compared to the unweeded treatment. The number of grains per pod and weight of 1000 seeds were significantly affected at high densities of E. dentata (55 plants m-2). High correlation levels were found between soybean seed yield, number of pods per plant and weight of 1000 seeds (98 and 85 % respectively).

Euphorbia dentata es una maleza anual, de ciclo primavero - estival que está presente en el 85% del área agrícola del partido de Azul, Pcia Buenos Aires Argentina, con densidades que oscilan entre 20 a 200 plantas m-2. Estudios en campo fueron conducidos durante dos años para determinar la relación de competencia entre soja y E. dentata a través de la evaluación del efecto de distintas densidades de la maleza sobre los componentes del rendimiento del cultivo y su biomasa. El peso seco y rendimiento de soja mostraron una respuesta dependiente de la densidad y de la biomasa de la maleza, siendo reducidos al 80% por la interferencia a partir de la densidad de 20 plantas m-2. En el rango de densidades estudiadas se observó una respuesta lineal que fue ajustada a una ecuación de regresión que indica que la producción de semillas de soja decrece 6,73 kg ha-1 por el incremento de cada planta m-2 de E. dentata. De los componentes del rendimiento del cultivo, el número de vainas por planta fue el más severamente afectado por la competencia obteniéndose reducciones del 40% respecto del tratamiento sin maleza. Altos niveles de correlación fueron observados entre el rendimiento de soja, el número de vainas por planta y el peso de 1.000 semillas (98 y 85% respectivamente).