Fumigants Can Stop Internal Decay of Wood Products

Pressure treated Douglas-fir distribution and transmission poles that contained little or no advanced internal decay, but a high fungal population internally at the ground-line zone, were selected for treatment. The fumigants were placed in holes drilled in the poles within 2 feet above the ground line. A wrap was applied to most poles from about 6 inches below to 3 feet above the ground line. The poles were bioassayed annually by removing increment cores and incubating them on malt agar for 3 weeks to detect the presence of fungi. Vapam (sodium N-methyl dithiocarbamate), Vorlex (methylisothiocyanate and chlorinated C3 hydrocarbons), and chloropicrin (tri chloronitromethane) greatly reduced or eliminated the fungal population in poles and were considered effective for stopping decay. A fumigant retreatment cycle of not less than 5 years appears feasible. Wrapping fumigated poles to slow loss of the fumigant is unnecessary.

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