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
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.