Resumo. The aim of this work was to evaluate the behavior and the correlation between the development of loblolly pine seedlings and weed competition in reforestation areas over 24 months in order to be able to make the appropriate management of weed competition and reduce the use of agrochemicals. The experimental design was a randomized block with 8 treatments (weed control with glyphosate herbicide at different times) and 4 replications: (control without control, full control of the weed competition and control of weed competition at 2, 4, 6, 8, 10 and 12 months after planting the seedlings in the field). The plot dimensions were 20 x 30 m (600 m²). After installing the experiment, 24 central seedlings per treatment were evaluated regarding: survival (%), height (cm), stem diameter (cm) and factor of production (cm³), at 6, 12, 18 and 24 months after transplanting the seedlings to the field. Based on the results, it can be concluded that survival and seedling height were not affected by the period of coexistence between weeds and their control, however the stem diameter and the factor of production (cm ³) were influenced by the coexistence period once the period when occurred the largest weed interference in the young plants was during the first year of the forest establishment.