Microscopic characteristics of microbial attacks of CCA-treated radiata pine wood
A P Singh, R N Wakeling
Light and electron microscopic observations were made of CCA-treated radiata timbers, which had been placed in service in a vineyard soil as supporting poles and as part of a house pile, to determine the cause of their deterioration. The house pile had failed in service after between 9 and 13 years and was of particular interest because decay was more severe in deeper regions than at the surface and attack was present up to 750 mm above the groundline. It was clear from transmission electron microscopy (TEM) that the predominant type of attack in the house pile was caused by erosion bacteria. The erosion patterns seen under the light microscope as troughs, pits and shallow depressions in the cell wall were almost certainly caused by erosion bacteria. However it was not entirely clear what had caused degradation patterns seen as fine channels under the light microscope. Soft rot was seen in outer regions of the post at the groundline but was very rarely seen in deeper regions. The vineyard posts had been attacked by tunnelling bacteria and soft rot. These studies demonstrated the importance of using both the light microscope and TEM in evaluating the cause of wood decay.