Recent work at FPInnovations has evaluated chemical treatments to prevent the formation of extractive stain in western redcedar. It is not known whether the control of extractives stain in western redcedar (WRC) by chemical treatment is purely interference with chemical processes such as leaching, re-deposition, and polymerization, or interference with a biological process, such as cleaving ester linkages to hemicellulose, which would free up phenolics to undergo these chemical processes. The present work reports on the performance of treated and untreated samples in a field test after four to eight months of exposure, and investigates the potential role of microorganisms in formation of WRC extractives stain. In accelerated testing, all treatments delayed stain formation by two to four months. However, after six months in test, a majority of samples from all treatment groups exhibited extractives stain. In laboratory tests, extractives stain formed under conditions not conducive to biological activity.