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The nematicidal activity of garlic extracts is known on root–knot nematodes but never investigated on the grapevine nematode <i>Xiphinema index</i>. In this study, the nematicidal activity of a commercial garlic extract formulate (GEF) was assessed on <i>X. index</i>, both in vitro and in a pot assay. In the in vitro assays, mixed specimens of <i>X. index</i> were exposed to a 0–4 mL L⁻¹ range of GEF concentrations, checking nematode immotility and mortality after 2, 4 or 8 h. In the experiments on potted grapevines, plants cultivated in soil infested by <i>X. index</i> were irrigated twice at a 15-day interval with 0.05, 0.2 and 0.5 mL L⁻¹ solutions of GEF, including nontreated soil as a control. An almost complete mortality of <i>X. index</i> specimens occurred after a 2 h exposure to a 2 mL L⁻¹ GEF concentration, while an 8 h exposure to even the 0.0312 and 0.0156 mL L⁻¹ solutions resulted in about 50% and 30% mortality, respectively. Soil treatment with a 0.5 mL L⁻¹ GEF solution significantly reduced the population of <i>X. index</i> and increased the grapevine root growth compared to nontreated soil or soil treated with the lower dosages. Results of this study indicated that garlic-based nematicides could be an effective tool for <i>X. index</i> management in organic and integrated vineyards.