Ammoniacal Zinc Oxide Treatment as An Inhibitor of Fungi in Pine Lumber

An ammoniacal zinc oxide system which imparted good water and light resistance to wood was examined for its effectiveness in controlling mold and other fungal discolorations during the storage and seasoning of green eastern white pine lumber. Freshly sawn boards containing both sapwood and heartwood were obtained from a sawmill and kept under cover for 8 days in a conditioning room maintained at 41?F and 95 percent relative humidity. Treated boards and controls were inoculated with a spore and mycelial suspension of Aureobasidium pullulans and Alternaria alternata, two fungi causing bluestain in pine sapwood. During the storage time the boards were also exposed to spores of molds that were present on other wood material in the storage area. In leaching experiments 10 treated air-dried boards and 10 air-dried controls were kept under running water for 48 hours and were stored for exposure to molds for 10 days. Molds appeared on the undipped controls within 3 days. No fungal growth occurred on the treated boards after 1 week except on wane and bark. By the completion of the seasoning period over 50 percent of the controls had moderate to extensive growth of molds. Only 1 (2.8 percent) of the treated boards had moderate mold growth and only on wood adjacent to wane. The remainder of the treated boards had none or slight mold adjacent to the wane. After skip-planing 44 percent of the controls still had moderate to extensive sapstain; the remainder, had mostly slight stain. In comparison, 1 (2.8 percent) of the treated boards had a small area of moderate stain adjacent to wane; the rest of the board was unstained. Some 78 percent of the treated boards were, unstained or had only very slight stain. The remainder had only slight stain. All of the leached controls had extensive mold, whereas only a few scattered spots of mold growth occurred on the treated leached boards. These scattered colonies appeared to be confined to areas where drops of water remained on the treated boards during part of the 10-day storage. All mold discolorations were removed by skip-planing.

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