Movement and Persistence of Chloropicrin Fumigant in Western Redcedar Poles

Fumigant treating has been effective in eradicating decay fungi causing internal decay in Douglas-fir poles but its suitability for western redcedar, whose heartwood is virtually impermeable to liquid preservatives, was unknown. To investigate this, the fumigant chloropicrin was placed in holes drilled at midlength of four 3-m sections of western redcedar poles standing vertically in the laboratory. Movement of its vapor in the heartwood was monitored by three different bioassay techniques using the decay fungus Poria placenta as the vapor-sensing agent. Lethal quantities of chloropicrin moved vertically to a distance of 1.2 m at average rates of 0.2 to 0.5 m per month. By the 3rd month, vapor had thoroughly permeated all pole sections and lethal concentrations were still present throughout 2 years later when the trial was terminated. Diffusion of chloropicrin in western redcedar compares favorably with that observed in Douglas-fir.

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