Disclosed is a wood preservative composition comprising micronized copper and copper-amine complex, wherein the copper component of the copper amine complex is from about 5% to about 50% by weight, based upon the total weight of copper in the composition. The copper amine complex serves to avoid wood surface chalking that is otherwise attributable to the presence of micronized copper in copper-based slurries used to treat wood products. In addition, the copper-amine complex enhances the antimicrobial efficacy of the composition when used in wood treatment applications by facilitating cell wall penetration of the treated wood.