Termite resistance of borate-treated lumber in a three-year above-ground field test in Hawaii

IRG/WP 00-30236

J K Grace, R J Oshiro, A Byrne, P I Morris, K Tsunoda

A protected above-ground field test simulating the sill plate (dodai) used in conventional Japanese housing construction was established in both Hawaii and Japan to examine the efficacy of disodium octaborate tetrahydrate (DOT, 2% and 3% shell and through) wood treatments. In Hawaii, chromated copper arsenate (CCA, 4 kg/m3) and ammoniacal copper zinc arsenate (ACZA, 4 kg/m3) were included in the test, along with untreated western hemlock and Pacific silver fir controls. Both field sites support active Formosan subterranean termites, Coptotermes formosanus Shiraki, although termite pressure is greater in Hawaii probably due to the uniformly favorable environmental conditions. After three years, minor damage (visual rating of 7) has been noted to four individual treatment dodai (out of a total of 10 boards per treatment) as follows: 2% BAE shell treatment (1 board), 2% BAE + DDAC through treatment (2 boards), and CCA treatment (1 board). These same individual boards had been also rated 7 in the second year of the study; and, although at year 3 termites are still present on the boards in each case, there has been no further visible deterioration. This supports an hypothesis of delayed deterrence from termite exposure to these nonrepellent treatments. In contrast, untreated control boards in Hawaii were completely destroyed within one to two years. Overall, all treatments have provided very good protection from termite attack over the three years of the study, with 9.3 representing the lowest mean rating. These results support the use of DOT, CCA or ACZA treatments to protect dodai from termite attack.


Conference: 00-05-14/19 Kona, Hawaii, USA

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