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ABSTRACT: David’s Spurge is an spring-summer annual weed, present in the central area of Buenos Aires Province, Argentina. Field studies were carried out during 2011/12 and 2013/14 to assess demography and population dynamics and determine a thermal time scale of this species. At the experimental site, 1 m² quadrants were established as observational plots, four per cohort. The number of individuals at each phenological stage and from each cohort was recorded weekly. At the end of the experiment, all plots were harvested, and seed production was determined. A thermal time scale was established to identify the occurrence of the different phenological events. Three cohorts were detected, the first one emerged in mid-October, the second one in early November, and the last cohort varied from late November till early January, totalling an average of 1,500 m-2. Over 80% of the evaluated emergences belonged to the first and second cohorts in both periods. Thermal time requirements calculated to reach the 2-4 leaves, 6-8 leaves, branching, and flowering stages, were 192, 370, 515 and 1,155 oCd, respectively. Average seed production in the first, second and third cohort was 5,700, 6,400 and 1,900 seeds m-2, respectively. However, the total number of propagules from the sum of the three cohorts was similar in both years, about 14,000 seeds m-2. Results from this study will foster a better understanding of the ecophysiology of Euphorbia davidii in the study area, and it may be a valuable contribution from an integrated weed management perspective.

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 davidii Subils, es una maleza anual que está presente en la zona centro de la provincia de Buenos Aires, Argentina. Se realizaron estudios para determinar el banco de semillas de esta especie y su distribución vertical en lotes agrícolas de Azul y Olavarría. Se extrajeron 240 muestras de suelo, provenientes de 60 puntos distribuidos al azar, a cuatro niveles de profundidad: 0-5 cm, 5-10 cm, 10-15 cm y 15-20 cm. Las extracciones se realizaron dos veces al año, en mayo y en septiembre. Las muestras fueron procesadas y las semillas separadas por tamizado en húmedo. Se evaluó germinación y viabilidad mediante la prueba de trifeniltetrazolio. Se cuantificaron 30.000 y 15.000 semillas m-2, para los lotes de Azul y Olavarría, respectivamente. En Olavarría, el 79% de las semillas se encontraron de 0-5 cm, de profundidad, el 14%, de 5-10 cm y el 7% restante de 10-20 cm. En Azul se observó una distribución vertical más homogénea. El 55 % de las semillas se encontraron de 0-5 cm de profundidad, un 24% de 5-10 cm, el 16% de 10-15 cm y el 5% en el muestreo más profundo. Las diferencias en la distribución se asociaron al manejo de los lotes. En ambas localidades la viabilidad de semillas, provenientes del estrato superficial, superó el 70%. Las semillas de estratos superficiales recolectadas en el lote de Olavarría, inmediatamente después de la dehiscencia, presentaron dormición, en cambio en las semillas provenientes del lote de Azul para el mismo momento de muestreo, no se observó dormición.

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 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 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).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 Michaux é uma espécie de ciclo primaveril-estival, de recente introdução na zona central da Província de Buenos Aires. Nos últimos anos, no distrito de Azul, adiquiriu importância como planta daninha ocupando uma grande área agrícola, principalmente de soja, milho e girassol. Atualmente, o pouco conhecimento desta espécie dificulta o emprego de métodos de manejo racionais e eficientes. O objetivo deste trabalho foi determinar a área de difusão desta planta daninha na região de azul; descrever suas características botânicas e estudar o seu comportamento nesta área através de diversos aspectos biológicos que pudessem ser relevantes para estabelecer programas de controle. Os estudos foram desenvolvidos em toda área agricultável da região durante os anos de 1993/94, 1994/95 e 1995/96. Nas áreas de amostragem determinou-se a presença e densidade e, diversos aspectos relacionados a biologia como emergência, germinação, número de frutos e sementes por planta e peso seco. Determinou-se a viabilidade das sementes e descreveu-se botanicamente a espécie. Verificou-se que a espécie ocupa uma superfície aproximada de 250.000 ha, o que representa 40% do distrito de Azul e 85% da área cultivada, com níveis de infestação que vão desde 20 a 200 plantas/m2. Sob condições naturais ocorrem dois picos de emergência e, a floração foi induzida pelo fotoperíodo. Em geral as plantas produzem uma grande quantidade de sementes e com alta viabilidade. Para um melhor conhecimento da espécie, esta encontra-se descrita botanicamente.Euphorbia dentata Michaux is an annual species which grows during spring and summer. Its has been recently introduced in the Province of Buenos Aires. In Azul district, during the last few years it has become an important weed with increasing propagation occuping a high proportio of agricultural land associated mainly with soybean, corn and sunflower crops. At present the limited available knowledge about this species makes difficult a rational and efficient management. Field studies to determine the propagation in the district of Azul, were conducted during three years. To check its propagation, enquiries to farmers were made. Also, all over the district, a transect across the agricultural land was conducted to survey several biological characteristics. The presence, density, emergence, germination, fruit and seed number per plant and dry weight were determined. Seeds have high viability. Its was demonstrated that the species occupies na area of approximately 250.000 ha that represent 40% of the district and 85% of the cultivated land, with levels of infestation from 20 to 200 plants per square metre. Under natural condition the weed shows two peaks of emergence and flowering is induced by day lenght. The species is described in detail and illustrated.

En el sudoeste bonaerense de la República Argentina, avena fatua es una maleza que ocupa una significativa proporción del banco de semillas presentes en el suelo, causando severas pérdidas de rendimiento en los cultivos de trigo, lo cuál la caracteriza como una maleza invasora. A pesar de que en los cultivos, se utilizan normalmente prácticas de control com graminicidas selectivos, se observa una alta incidencia de la población de Avena fatua a través de la determinación del número de panojas y semillas por metro cuadrado remanentes de las plantas que escapan al control y que alcanzan el estado reproductivo antes de la cosecha del cereal. El objetivo de este estudio fue evaluar el efecto de varios graminicidas postemergentes selectivos para el cultivo de trigo sobre el crecimiento de la población de Avena fatua por metro cuadrado en un diseño estadístico de bloques al azar con cuatro repeticiones. Los tratamientos fueron los siguientes: testigo sin control, tralkoxydim (150 y 200 g/ha), fenoxaprop-p-etil (69 y 83 g/ha), pirifenop-n-butil (50 y 55 g/ha) y diclofop metil (510 y 570 g/ha). En la primer campaña, con una baja infestación de la maleza (153 plantas/m2), todos los herbicidas y dosis probadas ejercieron una drástica reducción de los parámetros evaluados, no detectándose diferenciais significativas entre sí al evaluar el control por medio del número de panojas y semillas producidas por las plantas que escaparon al control. En cambio en la Segunda campaña com 285 plantas/m2 y habiéndoses realizado la aplicación delos avenicidas en un estado fenológico de la maleza más avanzado, el número de semilhas por metro quadradofue reducido a niveles que oscilaron entre un 60% y un 95% respecto del testigo sin control, detectándose diferencias entre los tratamientos. No obstante la reducción lograda, se comprobó en ciertos casos, un importante aporte de semillas que anualmente retornan al suelo, lo que podría significar sino un aumento, por lo menos un mantenimiento del número de porpágulos en el banco.Wild oats is na important weed in wheat in the southwestern Pampas of Argentina representig a high percentage of the soil seed bank. Even though specific herbicice are use, a high number of panicles and seeds survive. The aim of this study was to evaluate the effect of post emergence selective graminides upon the development of the wild oats seed bank in a wheat crop. The experiment was conducted in a randomized block with four replications. The treatments were: a) control (no herbicides), b) tralkoxydim (150 and 200 g/ha), c) fenoxaprop-p-etil (69 and 83 g/ha), d) pirifenop-n-butil (50 and 55 g/ha), and e) diclofop metil (510 and 570 g/ha). All herbicides were used at the recommended rates. In the first year, with a low infestation level (153 plants/ m2), all herbicides had a good effect. No differences between treatments were observed. In the second year, with a high level (285 plants/m2), the production of wild oats seeds was reduced to between 60% and 95% compared with the control and there were differences between treatments. Despite the effectiveness of the treatments, the seed produced were enough to keep the seed bank constant.