A method of preserving wood includes injecting into the wood an effective amount of a aqueous wood-injectable biocidal slurry, said a wood-injectable biocidal slurry containing dispersants and sub-micron biocidal particles selected from at least one of the following classes: 1) a plurality of particles containing at least 25% by weight of a solid phase of sparingly soluble salts selected from copper salts, nickel salts, tin salts, and/or zinc salts; 2) a plurality of particles containing at least 25% by weight of a solid phase of sparingly soluble metal hydroxides selected from copper hydroxide, nickel hydroxide, tin hydroxide, and/or zinc hydroxide; 3) a plurality of particles containing at least 25% by weight of a solid phase comprising a substantially-insoluble organic biocide selected from triazoles, chlorothalonil, iodo-propynyl butyl carbamate, copper-8-quinolate, fipronil, imidacloprid, bifenthrin, carbaryl, strobulurins, and indoxacarb; 4) a plurality of particles containing on the outer surface thereof a substantially-insoluble organic biocide; 5) a plurality of particles containing a solid phase of a biocidal, partially or fully glassified composition comprising at least one of Zn, B, Cu, and P. The particles may advantageously contain metallic copper, a leachability barrier, pigments, dyes, or other adjuvants disposed on the outer surface thereof.