Effects of tree stump treatments for reducing <i>Armillaria</i> root disease within conifer plantations of southeastern British Columbia

Root disease caused by the fungal pathogen, Armillaria solidipes, is commonly managed for in tree plantations of southeastern British Columbia by removing stumps before planting trees. The potential biocontrol, Hypholoma fasciculare, has been applied less commonly. We summarize the effects of mechanical stump removal and Hypholoma treatments on the development of 13 experimental conifer plantations aged 13–43 years consisting primarily of Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco), lodgepole pine ( Pinus contorta Douglas ex Loudon), and western larch ( Larix occidentalis Nutt.). Generalized additive models were used in the Akaike information criterion model selection with response variables chronologized for each treatment unit: Armillaria incidence, survivorship, basal diameter, diameter at breast height, height, and basal area index. Stump removals reduced Armillaria incidence in the oldest stands from 3.3% to 1.1%, increased survivorship from 30.3% to 69.7%, and produced 1.72 times greater basal area index. Armillaria reduction with stump removals was greater on Douglas-fir and western larch. At year 21, Hypholoma reduced Armillaria occurrence by 2.1 percentage points, whereas stump removals decreased Armillaria by 1.7 percentage points. Treatment decisions need to weigh silvicultural gains with financial and environmental costs, while Hypholoma treatments warrant expanded research.