Fumigants Can Stop Internal Decay of Douglas-Fir Poles for At Least 5 Years

To stop internal decay of Douglas-fir transmission poles pressure-treated with pentachlorophenol in heavy oil, two pints of agricultural fumigants (chloropicrin, Vapam, or Vorlex) were placed in 7 holes within 3 feet above the ground line in each of 32 poles. Changes in fungal population were followed annually by removing 12 cores from 1 foot below to 4 feet above the ground line of each pole and incubating them on malt agar for 3-4 weeks. Cores then were examined for outgrowth of decay and nondecay fungi. Distribution of fumigants in poles was studied by enclosing core segments in tubes with an inoculum of a decay fungus on malt agar and noting the inhibition of the growth of the fungus. The fumigants decimated or eliminated the fungal population within 1 year and maintained the population of decay fungi at a low level for 5 years. The population of decay fungi has begun to increase in Vapam treated poles, and the population of nondecay fungi is increasing in all poles. A temporary wrap did not improve the effectiveness of Vapam. Four and one-half years after treating, chloropicrin and Vorlex vapors were detected as much as 8 feet above and below the ground line and within 1/4-inch from the faces of seasoning checks. Estimated retreatment cycles are from 6 to 7 years with Vapam and 10 years with chloropicrin or Vorlex.

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