Graduate Thesis Or Dissertation
 

Methylisothiocyanate as a wood fumigant : fungitoxicity to Poria carbonica in wood and gelatin encapsulation for use in wood products

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  • Experiments were conducted to determine both the influence of wood moisture content on the fungitoxicity of methylisothiocyanate (MIT) to the wood-decay fungus Poria carbonica, and the ability of gelatin to safely en-capsulate MIT for efficient treatment of wood products. The fungitoxicity of MIT was studied by determining the product of fumigant concentrations and exposure times necessary to kill 90% (CT₉₀ products) of the P. carbonica propagules in small Douglas-fir heartwood blocks. A continuous flow fumigation apparatus was developed that maintained constant fumigant concentrations in the air surrounding infested wood blocks. The effectiveness of MIT was determined by comparing estimates of the P. carbonica populations in the wood blocks before and after each fumigation treatment. The CT₉₀ products ranged from 46 to 179 μg° hr/ml air and were influenced by both wood moisture content (MC) and the duration of fumigant exposure. Fungi in wood at 20% MC required about twofold higher CT₉₀ products than fungi in wood at 40 or 75% MC, even though the 20% MC wood bound higher MIT concentrations. The increased fungal susceptibility in high moisture content wood should be beneficial as decay fungi are most active in wet wood. As fumigant exposures increased from 5 to 32 hr, CT₉₀ products decreased about twofold, indicating a greater fungal susceptibility to MIT during long exposures and low concentrations than during short exposures and high concentrations„ This suggests that low residual MIT concentrations may effectively prevent re-infestation of treated products. High concentrations of MIT bound to wood blocks during fumigations, but were rapidly lost during aeration indicating that MIT is loosely bound to the wood structure. The MIT bound to wood should extend the duration of residual fumigant vapor in treated wood. Gelatin encapsulation of MIT offers a safe and efficient method of storage, handling, and application of MIT for wood fumigation. Gelatin capsules did not significantly bind MIT or alter its fungitoxicity during storage, were impermeable to MIT vapors for over 1 year during dry storage, and readily released MIT when placed in moist wood. Gelatin encapsulated MIT was equally effective as non-encapsulated MIT in fumigations of small Douglas-fir heartwood blocks infested with P. carbonica. In wood pole sections, the addition of only a small quantity of water per treatment hole was sufficient for excellent release of MIT from gelatin capsules, and allowed rapid fumigant movement through the pole sections. The addition of larger quantities of water appeared to slight ly reduce fumigant movement. Both encapsulated and non-encapsulated MIT treatments produced substantially higher levels of MIT vapors moving through poles than was produced by the breakdown of Vapam in wood. This was the result of both the more concentrated form of MIT and the poor conversion of Vapam to MIT in wood. Gelatin encapsulation of MIT offers a safe method of applying a concentrated and effective fumigant to wood products for control of decay fungi.
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