A synergistic aqueous wood preservative composition comprising a copper compound and penflufen. The copper compounds of the compositions of the invention may be soluble, partially solubilized or micronized particles. The penflufen of the compositions of the invention may be solubilized, emulsified or particulate. The wood preservative compositions of the present invention are surprisingly provided as stable dispersions and confer surprising and unexpected resistance to treated wood and wood products.