Reducing Internal and External Decay of Untreated Douglas-Fir Poles: A Field Test

Laboratory culturing and a closed-tube bioassay with Poria placenta revealed that the fumigants chloropicrin and methylisothiocyanate effectively reduced the incidence of internal decay in non-pressure-treated Douglas-fir poles in ground contact for 3 years. The externally applied, chemically impregnated Osmoplastic wrap limited basidiomycete colonization at groundline but was less effective above this level. Application of preservative wraps at groundline apparently limited surface decay in this zone, while internally applied chemicals produced more variable results. Results suggest that a combination of externally applied paste and internally applied fumigant will effectively protect non-pressure treated poles against internal decay at or above the groundline. On the other hand, evaluation of surface decay by Pilodyn and radial compression tests and by microscopic examination produced inconclusive results, possibly because of the variable distribution of decay and incomplete chemical protection of the wood. A pick test was somewhat more conclusive. Monitoring of these test poles will continue.

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