Setaria viridis (green foxtail) is an invasive weed species in various agricultural systems, prompting the search for effective compounds to control its germination. The species has primary and secondary dormancy depending on the time elapsed since post-harvesting, making management strategies more difficult. Several weed plants, such as Lantana camara L., can be a source of allelochemicals with herbicidal effects, being a potential candidate for the control of S. viridis. We investigated the effects of L. camara extracts on the germination and initial growth of S. viridis seeds with different degrees of dormancy and revealed a dose-dependent bioherbicide effect. Aqueous extracts of L. camara were analyzed by HPLC-DAD and applied (0.1 to 5.0 mg/mL) to 12- and 110-day post-harvest S. viridis seeds. Seeds were evaluated daily and germination percentage (GP), speed germination index (SGI), and radicle length (RL) were calculated. Phenolic acids and flavonoids were major components of the extract. Lower concentrations (0.1 and 0.5 mg/mL) stimulated and accelerated the germination of S. viridis, breaking its dormancy. Both 1.0 and 5.0 mg/mL concentrations hindered germination, especially in 12 dph seeds. The 1.0 mg/mL concentration resulted in longer roots, whereas 5.0 mg/mL inhibited root development. Lantana camara extracts potentially stimulate germination and radicle growth of S. viridis at low concentrations while inhibiting these parameters at higher doses. These results may open new possibilities for using L. camara in weed-control strategies.
