Decomposition of methylisothiocyanate in Douglas-fir heartwood

Decomposition of the wood fumigant methylisothiocyanate (MIT) was studied in blocks of Douglas-fir heartwood. Decomposition was influenced by wood moisture content (MC), with decomposition rates estimated at 0.2, 0.9, and 1.6 percent per week of the total bound MIT for wood fumigated at 0, 12, and 60 percent MC, respectively. Dimethylthiourea and 2,4-dimethyl-1,2,4-thiadiazolidine-3,5-dithione, which formed during fumigation, showed toxic activity against the decay fungus Poria carbonica. Elemental sulfur was also formed, but showed minimal fungi toxic activity. Some MIT remained in fumigated wood even after extensive aeration under dry conditions. This residual MIT rapidly volatilized at fungitoxic concentrations when wood was wetted and may provide residual protection against fungal invasion.

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