Chloropicrin movement and fungitoxicity in decaying southern pine laminated timbers Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6t053j613

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  • Three groups of experiments were performed to determine an effective procedure for controlling decay in southern pine (Pinus spp.) laminated timbers. (i) A decaying laminated arch of southern pine was treated with chloropicrin. Movement of the chemical vapor through the arch and its effect on the decay and nondecay fungal population were monitored. (ii) Fungitoxicity studies with three decay fungi isolated from the laminated arch were performed by exposing infected wooden wafers to fumigant concentrations for various lengths of time, and by monitoring fumigant concentration and death of fungi in treated wooden blocks over a 24-hour period. (iii) Vapor movement across gluelines and along the radial and longitudinal axes of southern pine blocks conditioned to a range of moisture contents was monitored. Fungitoxic chloropicrin vapors diffused about 2 m from the treatment sites in the laminated arch over a 13-month period. A vapor wrap enclosing a portion of the arch limited escape of chloropicrin from the wood and improved treatment. Diffusion along the length of the arch was much greater than that between laminates. The minimum lethal dosages of chloropicrin determined in infected pine wafers ranged from 1.73 to 18.40 [mu]g hrs/ml for Gloeophyllum saepiarium and from 13.44 to 15.00 [mu]g hrs/ml for Poria sp., for 24 and 4 hour exposure periods respectively. Chloropicrin concentration/time values in wood blocks were maximized at 30 to 60% wood moisture content indicating that treatment may be more effective at this moisture content range than at 8%. Movement radially through wood and across gluelines was severely limited when compared to longitudinal movement. The rate of chloropicrin diffusion through wood blocks decreased with increasing severity of incipient decay. Minimum lethal dosages of chloropicrin to decay fungi were higher in infected wood blocks than in infected wafers. The findings of this research support the following recommendations: (i) Decay may be controlled by treatment with 0.5 cc of chloropicrin per square centimeter of cross sectional area at appropriately spaced intervals along the timber. (ii) Treatment sites should be spaced at about 2 m intervals along the decayed length of the timber for wood at about 8% moisture content. Treatment sites should be spaced closer together for wood of higher moisture contents. (iii) Treatment holes should contact all laminates. (iv) A vapor barrier should be employed to retain fumigant vapors in the timber.
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