To avoid microbial wood discoloration, the generally suitable measures against fungi (e.g., Liese et al. 1973; Liese and Peek 1987; Grog et al. 1991; Yang and Beauregard 200 1) are listed in Table.
Felling in the cold season and fast processing of the stems through well coordination between forestry and wood industry reduces microbial activity during storage of the stems in the forest. Cool, shady, and ventilated storage without ground contact and with unhurt bark to maintain high wood moisture content and to prevent lateral infections are favorable. Lumber discoloration can be prevented by prompt air-drying in well-ventilated stacks protected against rain by a roof, or by kiln-drying. Wet storage of stemwood by sprin-kling or ponding protects against fungi and insects. Currently, stem storage is performed in a N2/CO2 atmosphere (Mahler 1992; Bues and Weber 1998; Maier at al. 1999).
Table : reventive measures to avoid microbial wood discolorations and decay
- felling in the cold season
- appropriate storage of fresh wood
- coordination between forestry and wood industry
- drying - wet storage
- storage in N2/CO2 atmosphere
- chemical preservation
During wet storage, however, wood quality may become reduced by degr, (Willeitner 1971; Karnop 1972a, 1972b; lotion oldie pits by anaerobic bacteria Adolf et al. 1972), by oxidative discolorations of phenolic compounds diffusing out ward (Höster 1974), and by brown discoloration of the outer . log parts through phenolics rom the bark (Peck and Liese 1987; Bues 1993).
Sprinkled stems were even colonized by A rmillaria mellea, which "drilled" a borehole from the bark into the xylem to provide itself with air and subse-quently decayed the wet wood (Metzler 1994). Discoloring fungi and molds may be rather tolerant towards several fungi-cides, which inhibit decay fungi. Numerous protective agents were investi-gated for their effectiveness against mold and blue-stain fungi: e.g., Karstedt et al. (1971), Wolf and 1,iese (1977), Nunes et al. (1991), Laks et al. (1993), Wakeling et al. (1993), and Suzuki et al. (1996).
Sodium pentachlorophenate (PCP-Na) had been used for dipping and spraying procedures against discol-oration and decay (Willeitner et al. 1986). In view of the negative impact on humans, animals, plants, and the environment, utilization of PCP and import of PCP-treated woods are however restricted in Germany due to contamina-tions of PCP with polychlorinated dibenzodioxines and dibenzofuranes as well as due to the development and release of these compounds during burning of PCP containing woods. Dependent of material and intended purpose, e.g., boron compounds, quaternary ammonium compounds or dithiocarbamates may be used . Solid wood, wood composites (Gardner et al. 2003), and gypsum wallboard treated with borate were tested for mold performance (Fogel and Lloyd 2002). Boron compounds were used against blue-stain in Norway spruce (Babuder et al. 2004) and rubber wood (Akhter 2005).
Despite felling during the cold season as well as using y ventilated stacking of the lumber, damage nevertheless occurs by blue-stai fungi. A two-year experiment with pine wood using different felling times and storage variations showed that damage of the round timber might be reduced and that rapid timber seasoning has the greatest influence (Schumacher and lli Schulz 1992). Un unsolved problem is the discoloration of bright tropical afterwo odfsei like ge Pycnanthus, Virola, Aningeria and Pterygota (Bauch et al. 1985), and during shipment and drying of the sawn timber.
Comments