Effect of preservative treatment on survival of fungi in western red cedar utility poles

The ability of fungi to survive in western red cedar utility poles through the thermal treatment process was explored by removing increment cores from 200 poles before and after treatment. The treatment processes were varied to produce maximum temperatures ranging from 17° to 80°C at the pith center of the largest pole in a given charge. Although approximately 20 percent of the poles contained some evidence of visible decay prior to treatment, only one decay fungus was isolated from these poles. It is generally difficult to culture decay fungi from western red cedar heartwood and our results confirm this problem. As an alternative, we used the incidence of non-decay fungi before and after treatment as an indicator of heat efficacy. The incidence of non-decay fungi declined by 93 to 100 percent, depending on the treatment conditions, suggesting that the treatment processes were capable of eliminating most fungi from the poles. The paradox between non-sterilizing temperatures and low fungal survival was believed to reflect the fact that most of the fungi were present in the sapwood, where they were affected more directly by heat and preservative treatment.