Use of biological agents to enhance the preservative treatment of electrical distribution poles
Treatment of timber with preservative varies from species to species. Poor preservative penetration has been associated with wood decay and shortened service life of treated timbers. The preservation of Sitka spruce and Scots pine heartwood by conventional methods is poor with the depth of preservative penetration being only a few millimetres. The use of Trichoderma isolates to improve the permeability, of such timbers provides a novel approach to timber treatment. Initial studies established that Trichoderma isolates varied in their ability to produce selected extra-cellular enzymes (cellulase, pectinase and amylase) which would be important in the improvement of the permeability of Scots pine and Sitka spruce material. On the basis of the ability of the organisms to produce extra-cellular enzymes in vitro, 5 isolates were selected and tested against dried and freshly cut small wood block samples. The high moisture content of green wood is recognised as being inhibitory to some colonising organisms. Results indicated that selected isolates were capable of growing through fresh wood samples and varied in their ability to improve the permeability of the samples. Methods best suited to determine the changes in permeability were developed and assessed. Two methods were finally used: a fluid uptake and an air flow method. Both methods were used to demonstrate the ability of the isolates to improve the permeability of Scots pine and Sitka spruce material. Two Trichoderma isolates showed a consistent ability to improve the permeability of pine and spruce material. These isolates were used to inoculate freshly felled roundwood log sections. The two Trichoderma isolates successfully colonised and improved the permeability of the timber. When taken into pole material the isolates continued to show improvements in the permeability and subsequent preservative penetration. Analysis of the preservative treatment of Trichoderma treated logs showed deeper penetration and higher loadings than in untreated control logs. In spruce the loadings in the preservative treated zone were increased by approximately 300% although this was still below the minimum retentions required by the electricity supply industry. Pine material showed increased loadings in the treated zone with the highest loadings being found in the outer regions of the pole material.
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