| Summary: | In the search of sustainable and environmentally friendly methods for weed control, there is increasing interest in essential oils (EOs) as an approach to reduce synthetic herbicide use. The phytotoxicity of <i>Thymbra capitata</i>, <i>Mentha</i> <i>piperita</i>, <i>Eucalyptus camaldulensis,</i> and <i>Santolina chamaecyparissus</i> EOs against the noxious weed <i>Erigeron bonariensis</i> were evaluated in pre- and post-emergence assays in greenhouse conditions. The EOs were applied at 2, 4, and 8 µL/mL, with Fitoil used as emulsifier. In post-emergence, two ways of application were tested, irrigation and spraying. Several germination parameters (germination %, mean germination time, and synchrony of the germination process) were evaluated in pre-emergence tests, and the phytotoxicity level was assessed in post-emergence. In pre-emergence, all EOs significantly reduced seed germination as compared to the controls, ranking: <i>T. capitata > E. camaldulensis > S. chamaecyparissus > M. piperita</i>. The effectiveness of all EOs varied with the tested dose, always following the rank 2 μL < 4 μL < 8 μL, with <i>T. capitata</i> EO showing full effectiveness even at the lowest dose. In post-emergence, <i>T. capitata</i> was the most effective EO, inducing a rather complete inhibition of plantlet growth at the highest two doses. These EOs demonstrated to have good potential for the formulation of natural herbicides.
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