Compositions and methods are provided for treating wood products to provide leachresistant protection against fungal decay, termites and other wood destroying organisms. The preservative compositions provided include ammonia-stabilized solutions of zinc and boron, preferably in a molar ratio of Zn:B of between about 0.4:1 and 5:1, and are essentially copper free. The preservative may be applied by vacuum and/or pressure treatment or dip treatment under atmospheric pressure.