A novel wood preservative with plant extracts in a cypermethrin mixture protects envelope-treated tropical kempas hardwood against Coptotermes termites when exposed to an above-ground indoor situation after evaporative ageing

Abstract

In keeping with sustainability initiatives in the commercial wood protection sector to develop cost-effective, environmentally acceptable wood treatment alternatives to traditional biocides, this paper reports on an above-ground test for protection against subterranean termite damage to blocks of termite-susceptible heartwood of tropical (Malaysian) kempas hardwood (Koompassia malaccensis). The blocks were envelope-treated (brush-on) with a novel wood preservative based on plant extracts in a cypermethrin mixture (Biocide 1: 0.16% cypermethrin, 0.08% tebuconazole, 2% vegetal extracts). A commercial permethrin-based LOSP (Biocide 2: 0.2% permethrin, 1.8% tributyltin naphthenate, 0.1% dichlorofluanid) applied in 3-minute dips served as the control treatment. The air-dried kempas blocks were H2-weathered under a rigorous laboratory volatilization regime (representing long-term evaporative ageing of treated wood for above-ground indoor use in prolonged H2-hazard class situations). The blocks were then exposed for 6 months above ground, inside a containerised test design targeting subterranean Coptotermes curvignathus termites, at a humid forest site (representing a severe H2-hazard class situation with treated wood isolated from wetting, soil contact, and weather). The results showed irrefutably that untreated kempas heartwood was severely attacked by C. curvignathus (mean mass loss: 70.4% and 20,416 mg) with a low mean visual termite rating (2.4). However, the treated kempas wood was well protected at very low surface retention of Biocide 1 (mean negligible mass loss: 0.66% and 207 mg) and very low surface retention of the control Biocide 2 (mean negligible mass loss: 1.01% and 306 mg), with both treatments similarly yielding the highest mean visual termite rating for all replicate kempas specimens (rating 10). The performances of the two biocides were similar but varied significantly (P < 0.05) from the attacks against their untreated counterparts. Biocide 1 therefore has considerable anti-termite potential and could replace conventional LOSP Biocide 2 treatments to protect wood exposed to a long-term H2-hazard class environment.