Biocides designed for prevention of indoor mold growth on wood-based materials need to provide long-term protection under conditions of high humidity. Specimens of kiln-dried southern pine and unseasoned southern pine, aspen, and Douglas-fir were dip-treated with borate-dimethylcocoamine (DMCA) supplemented with voriconazole, thiabendazole, or thujaplicin and evaluated at 4-week intervals for inhibition of three mold fungi, Aspergillus niger, Penicillium chrysogenum, and Trichoderma viride, using the ASTM D4445 mold test. After 8 weeks, all treatments of aspen and Douglas-fir inhibited growth of test fungi, while kiln-dried pine only inhibited A. niger and unseasoned pine only inhibited T. viride despite average chemical retentions in pine up to four-fold greater than those in aspen and Douglas-fir. After 12 weeks, aspen and Douglas-fir treated with the thiabendazole-containing biocide continued to provide protection against growth of the test fungi. The thujaplicin-containing biocide provided partial protection of aspen and Douglas-fir for 12 weeks but failed to protect pine samples beyond 4 weeks. A comparison of tebuconazole, propiconazole, voriconazole, and thiabendazole in the borate-DMCA biocide system showed that thiabendazole and voriconazole provided superior protection against the test fungi, particularly T. viride. We conclude that multicomponent biocides with thiabendazole protect aspen and Douglas-fir against growth of test fungi for at least 12 weeks under the conditions of the ASTM 4445 mold test.

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