AbstractThe aim of this study was to determine the antifungal and antimicrobial properties of madder root extract when used as an environmentally-friendly wood preservative and against blue stain. Plant dyestuff was extracted from the root of madder by using an ultrasonic assisted method and then applied to Turkish oriental beech, Scots pine, oak, and walnut wood blocks with the immersion (classic) and immersion + ultrasonic assisted methods. For mordants, ferrous sulfate, aluminum sulfate, copper sulfate, and vinegar were used. In order to compare the performances of the natural paints, a synthetic dye was used. The abilities of the extracts to suppress attack by brown rot (Postia placenta) and white rot (Trametes versicolor) were investigated. Treated blocks were exposed to P. placenta and T. versicolor attacks for 16 weeks according to the TS 5563-EN 113 method. Antimicrobial activity of the extracts was determined with the agar dilution method by using the disk diffusion method for bacteria. Results showed that the mordant mixes were considerably more resistant to fungal decay compared to their untreated and synthetic counterparts. In general, control (non-mordant) and vinegar mixtures showed good performance against brown and white rot fungi. Copper mixes showed better antimicrobial activity against all types of microorganisms. In conclusion, it was found that madder root extracts and mordant mixes could be used as wood preservatives.