Control of Heterobasidion in Norway Spruce Stands: The Impact of Stump Cover on Efficacy of Urea and Phlebiopsis gigantea and Implications for Forest Management

This study investigated the efficacy of Rotstop, a native Latvian Phlebiopsis gigantea strain and 35% urea solution in combination with a stump cover treatment to control against natural spore infection by Heterobasidion spp. upon precommercial thinning of Norway spruce in three stands growing on former agricultural lands. The major findings were that (i) infection rates of Heterobasidion spp. on stumps treated with the native P. gigantea strain, Rotstop or urea are similar when stumps are uncovered, and (ii) stump cover promotes stump colonization by the Latvian P. gigantea strain and Rotstop, leading to a significantly smaller relative area colonized by Heterobasidion spp., as well greater efficiency against Heterobasidion in comparison with urea. Covering of stumps appears beneficial for controlling Heterobasidion stump colonization and may be valuable to forest owners if used in small-scale operations, but it is impractical in automatized thinnings, where managers should consider using regular Rotstop without covering the stumps.