International comparison of three field methods for assessing the in-ground resistance of preservative-treated and untreated wood to termites and fungal decay – Summary of observations after five years

IRG/WP 03-20261

M Lenz, J W Creffield, T A Evans, B M Kard, C Vongkaluang, Y Sornnuwat, A F Preston

Results are presented from a five-year study conducted in five locations in Australia, Thailand and the USA. Three methods of exposure were assessed (below-ground, graveyard and ground contact) for evaluating the in-ground termite and decay resistance of Pinus radiata D. Don sapwood stakes that had been vacuum pressure impregnated with CCA (Type C) and ACQ (Type D) each at two nominal retentions (2 and 4 kg/m3), and of outer heartwood stakes from five trees of the durable North American Baldcypress, Taxodium distichum (L.) Rich. The termite attack and fungal decay ratings, based on the loss of cross section of the stakes, declined more rapidly at the three tropical sites in southern Thailand (Phuket) and in northern Australia (Darwin) compared to the two more temperate sites in southern USA (Gulfport, Mississippi) and southern Australia (Griffith, New South Wales). Depending on the type of preservative treatment (detailed for termites only) the three different assessment methods yielded either similar trends (ACQ 2 kg/m3; baldcypress) or outcomes varied with site and method (CCA 2 kg/m3; CCA 4 kg/m3) or the three assessment methods could be ranked from most to least effective in the same sequence across all sites (ACQ 4 kg/m3). Treatments or type of timber elicited different responses from the local termite fauna (from readily contacted by termites to avoidance). These responses can be modified by the way specimens are presented to termites. Average [n = 15] termite attack ratings (1st value Australian, 2nd value ASTM rating) after 5 years in the tropics (T) and non-tropics (NT) were: CCA 2 kg/m3 T = 4.3/6, NT = 6.7/8; CCA 4 kg/m3 T =5.5/7, NT = 7.4/9; ACQ 2 kg/m3 T = 4.4/6 , NT = 6.9/9; ACQ 4 kg/m3 T = 5.4/7, NT = 7.1/9. Baldcypress was more durable in the USA and Thailand (slight attack) and least durable against Mastotermes darwiniensis Froggatt in Australia (moderate attack). Fungus decay ratings (1st value Australian, 2nd value ASTM rating) after 5 years were: CCA 2 kg/ m3 T = 5.1/7, NT = 7.9/9; CCA 4 kg/m3 T = 6.1/8. NT = 7.8/9; ACQ 2 kg/m3 T = 5.2/7, NT = 6.7/9; ACQ 4 kg/m3 T = 5.6/8, NT = 7.7/9. Baldcypress results varied with source tree and test method.

Keywords: Subterranean termites, Isoptera; below-ground exposure method, graveyard method, ground contact method, CCA, ACQ, baldcypress

Conference: 03-05-18/23 Brisbane, Australia

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