Micronized copper azole (MCA) has been used extensively over the past decade to preserve southern pine, and other wide sapwood species. Treatment of refractory species is less common, in part due to concerns about treatability and resulting efficacy. To address these concerns, white spruce and Pacific silver fir stakes, and lodgepole pine and red pine posts, were pressure-treated with multiple retentions of MCA and placed in field tests in Canada in 2009 and 2010. After six years of exposure, untreated stakes were severely decayed while MCA-treated stakes were mostly sound, though low levels of decay were detected in some of the low retention samples. Untreated posts had failed or were severely decayed, while MCA-treated posts were sound at all retentions tested. These data indicate that MCA can be used to successfully treat refractory species, and that the resulting products resist decay in ground-contact exposures. Longer exposure time is needed to estimate service life.

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