Canadian Forest Service Publications
Heat disinfestation of mountain pine beetle-affected wood. 2007. Uzunovic, A.; Khadempour, L. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, B.C. Mountain Pine Beetle Initiative Working Paper 2007-14. 23 p.
Issued by: Pacific Forestry Centre
Catalog ID: 26792
Exporters of lumber and logs are obligated by Canadian law to apply approved treatments for phytosanitary purposes. Heating to 56oC for at least 30 minutes in a kiln or heating chamber (56/30) is the most common treatment used for lumber and is also an internationally accepted method to treat wood packaging in order to eradicate pests of concern. This time/temperature combination was originally developed to eradicate pinewood nematodes and their insect vectors. Questions have arisen in the marketplace about the efficacy of such treatment against fungal pests, and recently for those associated with mountain pine beetle-affected lodgepole pine. This project looked into the effectiveness of several time/temperature combinations, in particular whether 56/30 kills a selection of mountain pine beetle associated fungi including bluestain fungi (nine isolates), Ambrosiella fungi (three isolates) and sap-rot fungi (six isolates). Each isolate was replicated 6 times at all time-temperature combinations. In parallel we tested naturally infested lodgepole pine wood that was confirmed to be colonized with a mixture of bluestain, decay and mold fungi. The heat treatment protocol was developed through international collaboration and used heated water baths where test wood or glass vials (agar slants) with grown fungi were immersed and kept for a specified time after which the revival of fungi was attempted. Additionally, this project determined to what extent air-drying and wood aging reduced the viability of embedded fungi and if slow drying rendered the fungi more heat tolerant.
Leaving wood to air dry up to 4 months (to 15 % EMC.) was insufficient to eradicate fungi present in the wood and cannot be considered a fungal pest-eradication method. Some replicates have shown less heat tolerance if tested on agar slants so wood should be used to do such tests as it better represents a real-life situation. The data showed that 56/30 killed a majority of inoculated fungi grown on agar, inside wood test pieces, and those naturally found in substrate attacked by mountain pine beetle. None of the mixed bluestain fungi and decay fungi present in sapwood of naturally infested mountain pine beetle-affected trees survived 56/30; however, some survived when tested as pure cultures. All isolates and replicates of five of the species tested were killed at 56/30; however a sap-rot fungus Phellinus chrysoloma and a few replicates of bluestain fungus O. montium survived 56/30 (4 out of 12). All O. montium was killed by 56/60 and P. chrysoloma was killed at 61/30. These results should be considered to be worst case since the temperature was rapidly raised to the target and dropped rapidly after the target time period. In commercial heat treatments, the inherent tendency of kiln schedules to overshoot the target temperature and the insulating properties of wood will result in higher than target temperatures and the temperature being maintained much longer.
Heat treatment following prior wood air-drying showed some fungi developed heat tolerance when they were allowed to slowly desiccate; however, the evidence for this was limited. In pure cultures 19.0% (8 replicates out of tested 42) survived 56/30 after being air-dried for 90 days. This compares to 0% survival for immediate heat treatment and heat treatment after 15 and 40 days of air-drying. For the naturally infested wood no decay or stain fungi survived 56/30, regardless of prior air-drying; however some aggressive common molds e.g., Trichoderma spp showed a significant increase in heat tolerance and resource capture capability, preventing successful isolation of other fungi. We suggest that in a real-life situation where 56/30 will eradicate most of the fungi, these aggressive saprophytic molds (which are also commonly used a biocontrol agents) will most likely outcompete the weakened surviving bluestain or decay fungi, thus minimizing chances of their possible survival and threat of establishment in an importing country.