Polymeric nanoparticles containing the fungicides tebuconazole and chlorothalonil were prepared by a simple, surfactant-free method and found to have significantly smaller median particle diameters and more stable aqueous suspensions than their surfactant-stabilized counterparts. These more stable suspensions were delivered into southern yellow pine and birch wood with greater efficiency than the equivalent surfactant-stabilized nanoparticle suspensions. We found that the suspensions protected the treated wood against fungal attack by Gloeophyllum trabeum, a common brown rot wood decay fungus, and Trametes versicolor, a common white rot wood decay fungus, at low tebuconazole and chlorothalonil contents in the wood. Southern pine lost 5% or less of its mass after 55 days of exposure to G. trabeum when the tebuconazole or chlorothalonil content in the wood was only 0.4 kg/m(3), while a tebuconazole or chlorothalonil content of 0.8 kg/m(3) in birch wood was sufficient to bring its mass loss to less than 5% after 55 days of exposure to T. versicolor.