Essential oils are natural products capable of being used as novel agrochemical products. In order to fill knowledge gaps, this work evaluates the bioherbicidal potential of Schinus terebinthifolia fruit essential oil (EOsST) emulsions on germination parameters of Lactuca sativa and Urochloa brizantha seeds. The hydrodynamic size distribution of the emulsions was evaluated by dynamic light scattering (DLS), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR). Also, the chemical composition of EOsST was performed by gas chromatography coupled to mass spectrometry (GC-MS). DLS results suggest nanoemulsion (NE) particle sizes smaller than 735 nm and SEM images showed spherical and cuboid shapes. FTIR spectra indicate peaks at 1640 cm−1 and 1440 cm−1, referring to the benzene ring, and the C–H stretching band from 2970 cm−1–2870 cm−1 indicates the interaction between EOsST and TX-100. GC-MS reveals that the major compounds present on EOsST were α-pinene, germacrene-D, and β-pinene. U. brizantha seed germination was reduced at doses >2 mg mL−1 and completely inhibited at 32 mg mL−1. For L. sativa there was a reduction in germination which was dose-dependent and no dose caused total inhibition. Moreover, a decrease in photosynthetic pigments, flavonoids, phenolics, and total tannins was observed. Enzyme activity was altered, with reduction to catalase and peroxidase. Display omitted •Pre-emergent bioherbicidal activity of Schinus terebinthifolia Raddi essential oil was evaluated.•Morphophysiological damages were studied.•The photosynthetic pigments were strongly influenced by their presence in the nanoemulsion.•The enzymatic activity demonstrated the mode of action of the nanoemulsions.