Fumigation of red beech logs for reducing gray stain in lumber

The discoloration of sapwood of red beech (Nothofagus fusca) after kiln-dry ing has been an ongoing problem that lowers the wood's value for applicatio ns such as flooring and cladding. The occurrence of gray stain is noted aft er the drying and planing of lumber and is most likely similar to the enzym e-mediated or oxidative stain found in a variety of commercial U.S, hardwoo ds. Red beech logs harvested at the West Coast of the South Island of New Z ealand between 4 and 11 weeks prior were fumigated with sulfuryl fluoride ( as a methyl bromide replacement) and assessed for incidence of gray stain a fter normal commercial lumber processing. Fumigation of logs prior to dryin g increased yield of the highest-grade lumber (based on comparison to non-f umigated 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 resp ond to fumigation, and it is thought that gray stain precursors had accumul ated to a level sufficient to provide stain on drying despite killing of pa renchyma cells. Use of an antisapstain treatment of green lumber is essenti al for fumigated materials to control mold and fungal stain.