Imazapyr is a herbicide widely used for weed control in imidazolinone-tolerant sunflower. Imazapyr has a high potential for leaching into groundwater because it is highly water-soluble, persistent in soil, and only weakly sorbed by soils. There is a lack of information available in Argentina concerning groundwater leaching of imazapyr. Therefore, the objective of the present study was to determine the persistence and sorption of imazapyr in 3 Argentinean soils (Tandil, Anguil, and Cerro Azul sites). The presence and concentration of imazapyr were determined and quantified by ultra-performance liquid chromatography and tandem mass spectrometry. The persistence in soils followed the order: Cerro Azul > Tandil > Anguil, with half-life values of 121 d, 75 d, and 37 d, respectively. The half-life of imazapyr was negatively associated with soil pH and iron and aluminum content, and was positively related to clay content. Imazapyr sorption was found to be well described by the Freundlich isotherm. Soil pH and clay, iron, and aluminum contents were the main factors affecting the sorption of imazapyr. The sorption had a limiting effect on the degradation rate. Under certain conditions, the weak sorption and high persistence may increase the movement of imazapyr in the soil profile and the risk of groundwater pollution.

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Morphological characterization of Conyza blakei, Conyza bonariensis var. bonariensis, Conyza sumatrensis var. sumatrensis and Conyza lorentzii in the southeast of Buenos Aires (Argentine). The genus Conyza Less. includes ruderal species, which grow of ruderal habitat, roadsides and railways. They have also been cited as pasture weeds, annual and perennial crops under direct sowing (SD) systems, adapting to these slightly disturbed environments since they are sensitive to soil removal. The taxonomic identification of Conyza species linked to morphological characters is difficult in vegetative stages, since this genus has highly related and polymorphic species. With the objective of morphologically characterizing Conyza blakei, C. bonariensis var. bonariensis, C. lorentzii and C. sumatrensis var. sumatrensis were recorded 19 morphological characters (12 vegetative and 7 reproductive) qualitative and quantitative, in 35 plants of each species. These characters were analyzed by Multivariate Analysis (Analysis of Components and Main Coordinates). The morphological characterization made it possible to detect phenotypic differences between the Conyza species analyzed. The analysis of main coordinates allowed to differentiate the species both at a reproductive and vegetative level, while the analysis of main components only allowed to differentiate the species in reproductive stage.

Conyza genus includes herbs of ruderal habit, also referred to weeds in pastures, perennial crops, and no tillage crops. The insuitable use of herbicides, the incorrect identification of species, and the lack of monitoring, among others, explain the fact that Conyza species have become a growing problem in production systems under no tillage. Therefore, the knowledge of biology and the adaptive response to diverse cultural practices is paramount. Two of the most important characteristics to establish management guidelines are the height and growth stages of these species,since their herbicides sensitivity have been associated with these characteristics. The objective of this work was to analyze the results that affect the reproductive success (germination%, fecundity), and the most effective weed control time (height and determination of the phenological stages) of Conyza blakei, C. bonariensis, C. lorentzii and C. sumatrensis. Trials were conducted at the Agricultural Experimental Station of Balcarce, INTA, Argentina. We analyzed 35 individuals of each species. The germination % presented significant differences, being C. sumatrensis, the specie with the highest number of emerged seedlings. The phenological stages also showed differences, being C. bonariensis the species that began to elongate the stem earliest, the first in flowering, and the greatest fecundity. The senescence of the 4 species occurred within the first year of growth. The species with greater reproductive success would be C. bonariensis and C. sumatrensis, requiring the first earlier practices of controls.

RESUMENImazapir es un herbicida de amplio espectro de control de malezas, perteneciente al grupo químico de las Imidazolinonas. En Argentina se aplica a gran escala en los cultivos de girasol y maíz Clearfield ®. Debido a que posee baja capacidad de adsorción, alta capacidad de desorción y prolongada persistencia en el suelo, representa alto riesgo de lixiviación y de contaminación del agua subterránea. En Argentina es escasa la información generada al respecto. Por lo tanto, el objetivo de este trabajo fue determinar el riesgo de lixiviación del herbicida imazapir hacia el agua subterránea en tres suelos contrastantes del país (Tandil, Anguil y Cerro Azul). Se utilizaron los índices GUS (Groundwater Ubiquity Score), Factor de Retardo (RF) y Factor de Atenuación log-transformado (AFT), considerándose para el cálculo de este último tres recargas netas de agua subterránea: 0,3; 1,1; y 2,3 mm día -1 . Los índices fueron estimados empleando las propiedades ambientales (vida media y adsorción) de bases de datos y obtenidas experimentalmente para cada sitio de estudio. De acuerdo a los índices GUS y AFT, imazapir presentó alto riesgo de lixiviación hacia el agua subterránea en los tres suelos, según el orden Tandil > Cerro Azul > Anguil. Los resultados mostraron que una débil adsorción y una elevada persistencia podrían conducir a una alta movilidad de imazapir en el perfil del suelo, lo cual implicaría un alto riesgo de contaminación del agua subterránea.Palabras clave: imazapir, contaminación, factor de retardo, factor de atenuación, GUS, propiedades ambientales ABSTRACT Imazapyr is a broad-spectrum herbicide that belongs to the imidazolinone chemical family. In Argentina it is used on Imidazolinone-tolerant corn and sunflower Clearfield ®. Due to its low adsorption capacity, and high desorption capacity and soil persistence, imazapyr is prone to leaching into groundwater. There is a lack of information available regarding groundwater leaching of imazapyr in Argentina. Therefore, the objective of this study was to determine the risk of imazapyr leaching in three Argentinean soils (Tandil, Anguil and Cerro Azul sites). The indexes applied to estimate lixiviation risk of the herbicide imazapyr were GUS (Groundwater Ubiquity Score), RF (Retardation Factor) and AFT (Attenuation Factor log-transformed). The indexes were calculated