Fumigation of red beech in New Zealand for prevention of graystain
E L Schmidt, B Kreber
The discoloration of sapwood of red beech (Nothofagus fusca) after drying has been an ongoing problem which may lower value of material for certain applications (such as flooring) by as much as 50%. The dark gray stain noted after the drying and planing of lumber is not prevented by fungicide dips, and is most likely similar to the enzyme-mediated stain noted in a variety of commercial hardwoods. Fumigation of hardwood logs has proven successful in prevention of such non-microbial sapwood discoloration by killing of parenchyma cells presumably preventing buildup of stain and or enzyme precursors. Red beech logs were fumigated in New Zealand with sulfuryl fluoride (as a methyl bromide replacement) and graystain evaluations were done after normal commercial lumber processing. Fumigation of logs prior to drying increased yield of highest-grade materials by 300% (based on comparison to non-fumigated control log sections from the same trees). This increase was only noted for logs cut four weeks prior to fumigation, and older logs did not respond to fumigation. It is thought that in older logs, stain precursors had accumulated to a level sufficient to provide stain on drying despite killing of parenchyma cells. Fungicide dip of green lumber is essential for fumigated materials to control mold and fungal stain.
Keywords: RED BEECH; NON-MICROBIAL STAIN; FUMIGATION; GRAYSTAIN