Dynamics of Emergence and Intra-specific Competition in Conyza sumatrensis

Abstract

Conyza sumatrensis is one of the most problematic weeds in Argentina because of its high seed production, rapid germination and a high dispersal ability of the seeds. In the last years, its presence has increased in all areas under no tillage. Although it is a very prolific species, intraspecific competence may affect its behavior. The objective of this work was to evaluate the pattern of emergence of C. sumatrensis and the intraspecific competition as a self-regulation process. Trials were conducted at the Agricultural Experimental Station of Balcarce, INTA, Argentina. Weed emergency was recorded monthly. Competitive ability was assessed by the response of growth and fecundity to densities ranging between 0 to 600 plants m^-2. Emergence of C. sumatrensis was concentrated during the autumn (60 %) while a second peak was observed in the spring (20 %). The increase in plant density caused a decrease in height, number of branches and biomass (underground, aerial, and reproductive), as well as in seed production per plant. Growth and fecundity decreased until density reached 75 plants m^-2, above it they remained relatively constant. Results indicated a regulating effect on C. sumatrensis population that could restrict the reproductive potential of this species, and would also allow to estimate the optimal conditions to obtain certain sizes of plants and to evaluate the population responses to the application of the chemical treatments.