Wood preservatives extend the useful service life of all wooden commodities used above ground
and in ground contact. Over 50 years ago, the USDA-Forest Products Lab established tests in a high decay
and high termite hazard zone in southern Mississippi. During the last five decades, periodic reports have
been issued by researchers located at the USDA-FPL, in Madison, WI, on the efficacy and performance of
southern pine fence posts treated with a variety of wood preservatives. Since 1977, no report has been
issued by the USDA-FPL on the performance of these various preservatives in southern pine posts. This
study was undertaken to evaluate the long-term efficacy of over 50 wood preservatives in southern pine
wood in ground contact.
This study reassessed the condition of the treated wood posts in southern Mississippi, and statistically
calculated the new expected post life span. It was determined that commercial wood preservatives, like
pentachlorophenol in oil, creosote, and copper naphthenate in oil, provided excellent protection for posts,
with life spans now calculated to exceed 60 years. Surprisingly, creosote and penta treated posts at 75% of
the recommended AWPA retention, and Copper Naphthenate at 50% of the required AWPA retention, gave
excellent performance in this AWPA Hazard Zone 5 site. Untreated southern pine posts lasted 2 years in
this test site.