AbstractThe synergistic action of water-methanol (1:1 v/v) inner bark extract of barberry (IBEB) stem and biocide, propiconazole (PCZ), and non-biocidal additives, EDTA, BHT, and their combinations with various concentrations (50, 150, 250, 350, and 450 ppm) against the white-rot fungus, Trametes (Coriolus) versicolor was investigated. Results obtained herein demonstrated that IBEB by itself did not exhibit antifungal property, and enhanced protection was further observed by combining it with PCZ. BHT and PCZ showed inhibition percentages of 54.3% and 43.6%, respectively, against the growth of T. versicolor, which reached 75% with BHT at 50 ppm. A synergistic effect was found by introducing PCZ to IBEB when tested against T. versicolor in vitro, with an inhibition percentage of 62% at 150 ppm. No synergistic action was exhibited from the combination treatment of IBEB+EDTA+BHT, and the activity was enhanced by introducing PCZ to this combination treatment (50% at 350 ppm). Significant synergistic action between each of factors of IBEB+PCZ, EDTA+PCZ, and BHT+PCZ was found with inhibition percentages of 49.7%, 48.6%, and 52.7%, respectively. In conclusion, it is advised that IBEB and PCZ be used clinically at the same time.