Many fungal pathogens are associated with grapevine trunk diseases (GTDs), which cause important yield and economic losses in grape production. There are no effective control methods against GTDs once plants are infected, so research is aimed at preventive measures to avoid infections in nurseries and vineyards. Inhibitory activities of the phenolic compounds eugenol, epigallocatechin–3–O–gallate (EGCG) and thymol against the GTD fungi Diplodia seriata, Eutypa lata, Fomitiporia mediterranea and Neofusicoccum parvum were assessed in vitro, and in planta as grapevine pruning wound treatments. Greatest inhibition of pathogen mycelium growth was observed with eugenol (fungistatic at 1,500 µg mL–1, fungicidal at 2,500 µg mL–1). No inhibitory activity against GTD fungi was observed with EGCG. Minimum concentrations with in vitro inhibitory effects on D. seriata and N. parvum spore germination were 360 µg mL–1 for thymol and 750 µg mL–1 for eugenol. In the grapevine wound protection tests, thymol was effective against N. parvum at 360 µg mL–1, but eugenol was not.