Wood composites are rapidly being adapted for use in exterior applications. The incorporation of a preservative system to prevent fungus and insect attack is necessary with most exterior composites. Research studies were reviewed pertaining to organic preservative systems based on Lentrek* insecticide wood treatment which contains the active ingredient chlorpyrifos alone and in combination with tebuconazole and propiconazole (fungicides) for use as a combination treatment preservative system for solid wood and wood composites. Effective retentions for chlorpyrifos for protection of wood from termite and beetle attack was determined to be 0.2 kg/m3 set by the high retentions needed for field control of Coptotermes formosanus. In addition, this retention also provides effective control of the termites; Coptotermes lacteus, Reticulitermes flavipes, and Nasutitermes exitiosus, and the Lyctiid powderpost beetle, Lyctus brunneus. Retentions needed for control of Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot) were determined to be 0.11 kg/m3 and 0.06 kg/m3 for tebuconazole and propiconazole, respectively. Discussions with the manufacturers of tebuconazole and propiconazole indicated that the two fungicides work best together when in a 1:1 ratio. Given the need for the 1:1 ratio then, retentions needed for the tebuconazole and the propiconazole for treatment of wood composites are therefore 0.1 and 0.1 kg/m3, respectively, using tebuconazole as the benchmark. Tebuconazole and propiconazole retentions of 0.08 and 0.08 kg/m3, respectively, afforded moderate stain and mold protection of treated wood with a 64% reduction in stain and mold coverage by 3 weeks; thereafter, protection diminishes with time to a 40% reduction in coverage by 8 weeks. Overall, the retentions needed for a mixture of tebuconazole/propiconazole/chlorpyrifos (T/P/C) for use in wood composites are 0.1/0.1/0.2 kg/m3, respectively, to protect the wood from attack by insects and decay fungi while at the same time providing some moderate reduction of stain/mold coverage. Also, in order to compensate for the anticipated long term degradation of the two fungicides under field conditions, the fungicide retentions were increased by 50% thereby resulting in final recommended retentions for use of T/P/C in wood composites as 0.15/0.15/0.2 kg/m3, respectively.

Download document (184 kb)
free for the members of IRG. Available if purchased.

Purchase this document