Potential of heartwood extracts as wood preservatives combined with linseed oil in 8-year above-ground and in-ground field trials

Abstract

The current study assessed the efficacy of heartwood extracts from Tectona grandis, Dalbergia sissoo, Cedrus deodara, and Pinus roxburghii, combined with linseed oil, as protectants for two non-durable wood species against termites and decay fungi. Stakes measuring 45.7 × 1.9 × 1.9 cm and blocks measuring 12.5 × 3.75 × 2.5 cm of the sapwood of southern pine (Pinus sp.) and cottonwood (Populus sp.) were impregnated via vacuum pressure with individual heartwood species extract, linseed oil, or a combination of both. For comparison, solid heartwood stakes and blocks of the wood species used to obtain extracts were also included in the tests. All samples were exposed to decay and termites for eight years at a test site in southern Mississippi using ground contact (AWPA E7) and ground proximity (AWPA E26) tests. Results showed that combining heartwood extract and linseed oil resulted in greater resistance to termites and decay in cottonwood and southern pine compared to using only linseed oil or the individual heartwood species extract in both tests. However, most of the samples that were treated with the combination treatment failed and, in either test, these treatments were not as effective as commercially used wood preservatives, such as copper naphthenate (CuN) or disodium octaborate tetrahydrate (DOT). Additionally, solid heartwood P. roxburghii stakes and blocks decayed completely and failed due to termite attack after eight years in the field in both tests. After eight years in the field, C. deodara and D. sissoo stakes were severely attacked by decay and moderately to severely attacked by termites. Blocks of these two species exposed in a covered ground proximity exposure showed slight attack by termites and decay fungi. Tectona grandis stakes showed moderate decay damage and slight termite attack in the ground contact test. Blocks of T. grandis showed slight damage from fungi and termites in the ground proximity test after eight years in the field.