As a result of the activities of the mountain pine beetle which carries with it staining fungi, increasing amounts of bluestained wood are entering the marketplace. Bluestain is a visual defect caused by fungi that colonize the sapwood of trees, logs or lumber. Although typical bluestain fungi do not significantly impact mechanical properties, the wood is less desirable for appearance-grade applications. Bluestain is also associated with increased permeability, which could make it more suitable for preservative treatment. Methods are needed to identify stained lumber in the mill either to remove it from appearance grades or select it for preservative treatment. Detection of bluestain can be made visually, since it is an appearance grade defect. In industry, RGB colour coordinates are used to identify bluestained lumber. However beetle-affected wood from advanced grey stage trees is also anticipated to contain decay. Although the present research focuses on detecting bluestain only, a method of detecting both decay and stain would be preferable. Technology for detection of decay in pulp chips had been developed by Paprican and work is underway to evaluate its effectiveness on lumber.
The present research describes efforts to develop an automated spectroscopic system for identification of bluestained lumber. A large visible/near infrared spectrometer from FPInnovations – Paprican Division was used to scan motionless bluestained and clear 2 x 4” lumber on four sides. These spectra were used to model observed visual ratings of bluestain intensity using multivariate statistical methods. A Partial Least Squares (PLS) model developed from the top and bottom spectra was able to differentiate degree of staining. A PLS model from the side spectra was not able to differentiate stained and clear wood.