Fungal discoloration of coniferous sapwood (primarily pine and spruce) is caused by blue stain fungi (sap stain) belonging to the Ascomycetes and Deuteromycetes. The dark colored, large diameter hyphae penetrate wood by entering tracheids by way of ray cells (Fig. 1) and extract nutrients from the ray parenchyma. Optimal temperatures for fungal growth are between 18 and 29 °C. The structure and strength of wood are minimally affected by invasion of blue stain fungi, however the cosmetic damage caused by discoloration(s) can lead to considerable economic loss, both domestically and in the export markets.
Primary blue stain (i.e., stain occurring in standing trees) is initiated by fungal spores introduced into wounds in the bark caused by wind or insects. Secondary blue stain occurs in wood after sawing and during storage. It is a problem in wood which is insufficiently dry and which has been poorly stacked. Some authors distinguish between “blue stain” and “sap stain;” the former referring to stain occurring in poorly stored sawn wood, with sap stain referring to discolorations in standing trees and felled logs.
A study was undertaken to better understand the occurrence, distribution, and economic consequence of blue stain fungi in the forest region near Eberswalde, Brandenburg. Blue stain fungi occurring on pine were specifically analyzed. Forest and lumber companies were consulted for information relating to economic losses caused by blue stain.
Keywords: blue stain fungi, economic consequences, forest region
Authors
Wibke Unger
University of Applied Sciences, Potsdam, Germany
Steffen Krause
Paul Heydeck
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