Fumigation of red beech logs for reducing gray stain in lumber

The discoloration of sapwood of red beech (Nothofagus fusca) after kiln-drying has been an ongoing problem that lowers the wood’s value for applications such as flooring and cladding. The occurrence of gray stain is noted after the drying and planing of lumber and is most likely similar to the enzyme-mediated or oxidative stain found in a variety of commercial U.S. hardwoods. Red beech logs harvested at the West Coast of the South Island of New Zealand between 4 and 11 weeks prior were fumigated with sulfuryl fluoride (as a methyl bromide replacement) and assessed for incidence of gray stain after normal commercial lumber processing. Fumigation of logs prior to drying increased yield of the highest-grade lumber (based on comparison to non-fumigated control log sections from the same trees) providing the logs were not older than 6.1 weeks at the time of fumigation. Older logs did not respond to fumigation, and it is thought that gray stain precursors had accumulated to a level sufficient to provide stain on drying despite killing of parenchyma cells. Use of an antisapstain treatment of green lumber is essential for fumigated materials to control mold and fungal stain.

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