In this study the performance of copper naphthenate (Cu-Nap) and pentachlorophenol (Penta) treated pine stakes against decay and termite attack were compared at two test sites in Mississippi. Four different petroleum oils meeting AWPA Standard P9-A were used as carriers for these wood preservatives. After ten years exposure, the efficacy of Cu-Nap at a retention level of 0.05 pcf Cu was equivalent or slightly better than Penta at a retention level of 0.40 pcf. The type of carrier oil had an effect on the performance, but this was variable for both the type of preservative and test site. In comparing the two test sites, the performance of both preservatives was consistently better at the Dorman Lake test site. Wood treated with the oil carriers alone initially performed reasonably well against both wood decay fungi and termites, but the activity decreased rapidly after about six years exposure. Like the preservatives, the performance of the oils was consistently better at the Dorman Lake test site.

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