PROTECTING DOUGLAS-FIR PILE TOPS FROM INTERNAL DECAY - A 15-YEAR FIELD TRIAL

The ability of chemicals and caps, alone or in combination, to prevent top decay in Douglas-fir pile sections was investigated over 15 years . Culture of increment cores revealed that capping sharply limited fun gal colonization, as did application of the diffusible biocides ammoni um bifluoride or fluor-chrome-arsenic-phenol. A third diffusible bioci de, boron, was less effective. Applying pentachlorophenol, one of the pile-top treatments recommended by the American Wood Preserver's Assoc iation, in combination with a cap provided slightly less protection th an did capping piles that received diffusible treatments. Diffusibilit y appears to enhance markedly the effectiveness of remedial pile-top t reatments.