Variation in mold susceptibility among hardwood species under laboratory conditions

Wood packing materials (WPMs) utilized by the US Department of Defense (DOD) can be constructed with a diversity of wood species depending on end use. To extend service life, these materials are treated with preservatives to protect against insects and decay fungi. Recent issues have prompted the need to include moldicide additives with these treatments. The goal of this study was to evaluate mold susceptibility across a diversity of hardwood species with the purpose of identifying representative hardwood species that would be useful in differentiating efficacy of moldicide treatments in future studies. Conditioned hardwood lumber representing groups of species listed in DOD specifications were cut to obtain 7 × 20 × 70 mm specimens. The specimens were subjected to simulated rainfall to achieve the type of wetting that might occur in service, inoculated with mold spores, placed above moist paper in Petri dishes, and given visual ratings for mold growth at 2-week intervals. The results indicate that hickory, red oak sapwood, hard maple, white ash and white oak sapwood are all highly susceptible to mold growth. Mold growth was less consistent on aspen, cottonwood, and soft maple, and varied greatly between sapwood and heartwood for yellow poplar. Hickory, hard maple and white ash may be best suited for future WPM moldicide testing because of their availability and consistent mold susceptibility.