Ex-situ performance of extracts from naturally durable heartwood species and their potential as wood preservatives

Abstract

To avoid the use of toxic synthetic chemicals due to their potential environmental impacts, the feasibility of using heartwood extracts of Tectona grandis and Cedrus deodara as wood preservatives against the subterranean termite, Reticulitermes flavipes and two basidiomycete decay fungi, Trametes versicolor and Rhodonia placenta, was investigated in laboratory experiments. There were no significant differences in feeding for R. flavipes fed solvent-extracted and non-extracted T. grandis in choice and no-choice tests with 100% mortality. Reticulitermes flavipes ignored non-extracted C. deodara (mass loss 1.93%) in choice tests and consumed significantly more solvent extracted C. deodara (mass loss 33.4%) with 64.9% mortality. Complete termite mortality (100%) was observed after exposure to non-extracted C. deodara versus 53% mortality when fed on extracted C. deodara in a no-choice test. When extracted and non-extracted blocks of each wood species were exposed to decay fungi, durability of both heartwood species was reduced post extraction. Extracts removed from wood shavings via Soxhlet extraction were used to treat non-durable southern pine and cottonwood. Both extracts imparted termite resistance to the non-durable species. Weight losses of both non-durable species were reduced at the highest extract concentration tested (10 mg ml−1), and were inversely related to extract concentrations and retentions. Significantly higher termite mortality was observed at the maximum extract concentration tested for either extract. Water leaching of non-durable wood species treated with T. grandis extract did not reduce termite resistance, and no significant difference between mortality of termites on leached versus non-leached samples was observed. Conversely, the weight loss of wood treated with C. deodara extract was significantly greater post leaching. T. grandis and C. deodara extracts showed no protective effects at tested concentrations against decay fungi when applied to non-durable southern pine or cottonwood.