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.