Trials of new treatments for prevention of kiln brownstain of white pine (Pinus strobus)
E L Schmidt, E Christopherson, T L Highley, M H Freeman
White pine (Pinus strobus) often develops a surface brown oxidative stain when kiln dried. Such stain downgrades high quality lumber and is most likely to occur when fresh, unseasoned lumber is stacked during warm weather prior to kiln drying. Use of reducing agents or pH alteration has been successful, but may have some practical limitations for general use. This study attempted to prevent brownstain by killing living parenchyma in logs (an approach highly successful for hardwoods in prevention of enzyme-mediated stain) with methyl bromide. In addition, a new fungicide combination was tested for brownstain control. Fumigation of logs did reduce stain in dried lumber up to 45% but was much less effective than the fungicide dip (10 sec or 1 min at 0.3% a.i.). The fungicide formulation was an improvement over use of sodium thiosulfate and similar to sodium azide in trials at 2 laboratories. This co-biocide system should provide protection against both oxidative and fungal discoloration.