Borate-treated wood samples were tested for their resistance against subterranean termites in the field. Wood samples (10.5x10.5x40cm3) of western hemlock were pressure impregnated with disodium octaborate tetrahydrate (DOT) and didecyldimethylammonium chloride (DDAC), and assigned into two groups on the basis of boron contents:high retention (1.5-2.2%BAE) and low retention(O.7~1.3%BAE). Eight replicates were prepared for each retention level. Four untreated controls were also included in the field evaluation for comparison. Each sample was placed on a concrete block 19cm above ground surface and covered with plastic box in Kagoshima, Japan on July 1, 1993. Four boxes were employed so that 5 samples (two each of treated groups and one untreated sample) were in each box. After two years of exposure, three of all the treated samples exceptionally sustained very slight attacks, while in general untreated controls were moderately to severely attacked. Borate-treatment was proved to be satisfactorily effective in protecting lumber in above ground situations from subterranean termites. Further trials have been set up to determine the long-term efficacy of the treatment compared to chromated copper arsenate treated and naturally durable wood.

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