Biological control of intolerant hardwood competition: Silvicultural efficacy of Chondrostereum purpureum and worker productivity in conifer plantations

The vigorous vegetative reproduction of intolerant deciduous competition limits the efficacy of mechanical release operations in young softwood plantations. Applying bioherbicides such as the fungus Chondrostereum purpureum (Pers. ex Fr.) Pouzar could improve the effectiveness of release by reducing stump sprouting while gaining public acceptance. A field experiment was conducted in Québec (Canada) in two white spruce (Picea glauca [Moench] Voss) plantations invaded by intolerant hardwoods. This study compared four-year response of traditional mechanical release and mechanical release with an application of C. purpureum under the commercial formulation Myco-Tech™. The general objective of the project was to measure the silvicultural efficacy and worker productivity related to applying C. purpureum to control intolerant hardwoods in young white spruce plantations.The potential of C. purpureum was somewhat expressed four years after treatment by reducing paper birch (Betula papyrifera Marsh.) competition. However, because of the slight effect of the treatment on pin cherry (Prunus pensylvanica L.f.), red maple (Acer rubrum L.) and trembling aspen (Populus tremuloïdes Michx.), the addition of the biological treatment did not significantly improve light availability and morphological parameters (height, diameter) of white spruce seedlings. A 2.6-fold reduction in worker productivity compared to traditional mechanical release was caused by the additional operations and weight of the equipment used for the application of the Myco-Tech™ paste. The conditions that facilitate the operational application and effectiveness of C. purpureum applied in the form of the Myco-Tech™ paste do not seem to be present in young conifer plantations with a high density of intolerant hardwood competition.