This research aimed to study weed interference relationship on morphogenesis, yield, and greenhouse gas production potential of Urochloa ruziziensis under pasture renovation conditions. The experimental design was a randomized block design with four replications. Treatments consisted of seven coexistence periods: 0, 15, 30, 45, 60, 75, and 90 days after emergence (DAE). The following morphological parameters were analyzed: number of tillers, number of leaves, photosynthetically active leaf blade biomass, fresh stem biomass, dead material biomass, and total dry biomass. In vitro analyses of methane (CH4) and carbon dioxide (CO2) production were also carried out. The results were submitted to analysis of variance by the F-test, and the test of means was carried out by the Scott-Knott test at 5%. Biomass, CH4, and CO2 production of U. ruziziensis were modified with only 15 days of weed coexistence, with an effect even higher from 45 DAE. Therefore, weeds interfere with all morphological parameters, yield, and greenhouse gas production in the pasture establishment with the forage grass U. ruziziensis.