Stubs prepared from treated and untreated utility poles were installed in a test plot and pressure spade treated at the groundline with one of four preservative greases. At one and three year intervals, core samples were removed from the stubs and the improvement in the preservative efficacy due to the greases was assessed. The bioassay investigation showed that only bis(tributyltin) oxide (TBTO) and pentachlorophenol (PCP) reduced fungal growth, although chemical analysis of cores from the stubs suggested that the copper naphthenate grease treatment should also have enhanced protection. This observation may be related to the vapour pressures of the TBTO and PCP, the importance of which has not been established for the protection of wood products in service.

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