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RESUMEN -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.Palabras-clave: lecherón, labranza, propágulos, viabilidad. ABSTRACT -Euphorbia davidii Subils a summer annual weed, that is present in the center

A crop–weed simulation model is presented to compare and evaluate integrated weed-management (IWM) strategies. Specifically, the model was parameterized for soybean crops in competition with Euphorbia davidii Subils. We used both weed and crop demographic data surveyed in agronomic fields of the central zone of the Buenos Aires province, Argentina, throughout two crop cycles (2011/2012 and 2013/2014). The proposed model underwent a calibration process and subsequent validation with a 70/30% data split, (N = 37). Two annual-based and one multiannual-based case studies were simulated to demonstrate the performance of the model. Different IWM strategies were compared under both operational and tactical planning horizons through the evaluation of different model outcomes (i.e., crop yield, interspecific competition, economic return, and environmental impact). Our results suggest that the inclusion of cultural management practices could reduce both weed interspecific competition by 46 to 97%, and weed seed production by 40 to 89 %. An increment in both expected crop yield, by 6 to 20%, and annual gross margin, by 44 to 199 USD.ha−1, were obtained in silico for similar levels of environmental impact.

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.

Manuscrito recibido el 27 de julio de 2015 y aceptado para su publicación el 13 de noviembre de 2015. RESUMENEn el centro de la Provincia de Buenos Aires, durante la campaña agrícola 2014/2015 se registraron dos larvas endofíticas barrenadoras del tallo en rama negra. Para su identificación y estudio, ejemplares recolectados en las malezas fueron llevados al laboratorio para su disección. Las larvas encontradas correspondieron a dos insectos del Orden Coleóptera de las familias Curculionidae y Mordellidae. El barrenador Curculionidae pertenece al género Lixus y el de la familia Mordellidae es del género Mordellistena. Los adultos fueron obtenidos sobre las plantas trasplantadas y en los muestreos a campo sobre ejemplares de rama negra y en algunos casos refugiados dentro de las galerías. Si bien estos organismos pueden comportarse como enemigos naturales de rama negra, hay antecedentes de larvas de insectos barrenadores que interfieren con las prácticas de control químico, por limitar el transporte de herbicidas sistémicos. Palabras claves: Conyza spp.; Coleoptera; Larvas barrenadoras; Insectos endofíticos. Lixus and Mordellistena stem borer larvae in Hairy Fleabane (Conyza bonaeriensis L.) plants ABSTRACT Lixus and Mordellistena stem borer larvae in Hairy Fleabane (Conyza bonaeriensis L.) plantsIn the center of Buenos Aires Province, during the crop year 2014/2015 two endophytic stem borer larvae were found in Hairy Fleabane plants. In order to study and identify the species, samples of this weed were collected and taken to the laboratory for dissection. The larvae corresponded to two insects of the Coleoptera order, Curculionidae and Mordellidae families. The Curculionidae borer belongs to the genus Lixus and the Mordellidae borer was identified as Mordellistena genus. Adults Revista FAVE -Ciencias Agrarias 14 (2) 2015 Comunicación 2 | Revista FAVE -Ciencias Agrarias 14 (2) 2015 V. F. Juan et al.individuals were obtained from Hairy Fleabane in pots, and from field sampling plants, in some cases within the galleries. Even if these individuals can act as natural enemies of Hairy Fleabane, it must be pointed out that some background information mentions larvae of stem-boring insects, that may cause a negative effect on chemical control practices, as they limit the transport of systemic herbicides.