Canadian Forest Service Publications
Comparisons of B.t.k. aerial spraying strategies against the eastern spruce budworm, based on protection timing and intensity during a complete outbreak episode. 2018. Dupont, A.; Bauce, É.; Fuentealba, A., Hébert, C.; Berthiaume, R. In SERG International 2018 Workshop Proceedings. pp. 291-300.
Issued by: Laurentian Forestry Centre
Catalog ID: 39077
Availability: PDF (download)
Large-scale aerial spraying operations against the spruce budworm (Choristoneura fumiferana Clem.) with the biological insecticide Bacillus thuringiensis subsp. kurstaki (Btk), aims at maintaining trees alive during outbreak episodes. This objective is achieved when ≥ 50% of current-year foliage in balsam fir [Abies balsamea (L.) Mill.] stands is preserved. However, it is unknown if this standard approach used in Quebec province is always justified, or if less frequent interventions can provide similar results at lower cost. We conducted between 2010 and 2017 field experiments in Quebec's North Shore region to determine the efficacy of five different protection scenarios in protecting balsam fir, white spruce [Picea glauca (Moench) Voss], and black spruce [Picea mariana (Mill.) BSP] mixed stands. We hypothesized that less frequent Btk applications can provide an adequate level of protection. After nine years of defoliation, our results show a clear effect of protection scenarios on host tree species mortality caused by the spruce budworm. As the protection intensity decreases, the volume of balsam fir mortality increases (0% to 25%). Moreover, balsam fir mortality remains higher then spruce trees, but dead volumes are similar between white and black spruce species. At this stage of the outbreak, our observations suggest that balsam fir stands could be treated every 2 years, and white spruce every 3 years without significant mortality level (< 4%). Based on this study, it is possible to apply the required protection level at lower cost or on a greater forested area at a comparable cost.