A wood preservative paste consisting of borax and copper naphthenate has been tested to determine its efficiency in protecting wood from decay fungi and insects. The paste was applied to polyethylene-backed wraps that were fastened to the below-ground portions of unseasoned southern pine pole stubs. After 4 years of exposure in Mississippi, the untreated control stubs were completely deteriorated. The below-grade portions of the treated stubs remained sound after nearly 6 years of exposure due to movement of copper and diffusion of the borate throughout the cross section. Borate and copper also moved vertically in the stubs and was present in sufficient amounts to protect sections of the stubs as high as 3 feet above grade. After 9 years of exposure, the below-grade portions of the treated stubs had limited areas of decay and no termite damage; the majority of the cross section remained sound. Wood analysis indicated that concentrations of borate in the sound areas were about 1/10 the estimated toxic threshold. A visual examination and push test indicated that the treated stubs continued to be protected at groundline after 10 years of exposure. It is hypothesized that the continued protection of the below-grade portions of the stubs against both decay fungi and subterranean termites is the result of copper-borate complexes that have formed in the wood.

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