Is it relevant to treat against marginal spore infections of Heterobasidion spp. on birch?

Despite being one of the most economically important forest diseases in the Northern Hemisphere, the dynamics of Heterobasidion root rot in birch ( Betula pendula ) following thinning remain poorly understood. Assessing infection risk is becoming more relevant as birch gains importance in Fennoscandian forest management. This study examined (1) the incidence and severity of primary Heterobasidion infection of birch stumps following thinning across six stands in southern Sweden, (2) the efficacy of two biological stump treatments, Rotstop®S ( Phlebiopsis gigantea ) and Basinox® ( Pseudomonas protegens ), in reducing infection, and prompted by the high colonization of birch stump discs by Ophiostoma quercus , (3) in vitro interactions between O. quercus and Heterobasidion spp. on agar, and among O. quercus , P. gigantea , P. protegens and Heterobasidion spp. on wood. Overall, Heterobasidion incidence was low (0–6%), occurring exclusively on untreated control stumps; no infections were observed in treated stumps. While O. quercus was frequently detected, it did not exhibit consistent antagonistic effects against Heterobasidion spp. on agar, and responses on colonized wood pairings were variable. In contrast, P. gigantea consistently prevented Heterobasidion establishment on colonized wood, while P. protegens also reduced Heterobasidion growth in most cases, although less consistently. These findings indicate that primary Heterobasidion infection on birch following thinning is infrequent and limited in extent. Biological stump treatments were effective under the conditions tested, and given the low treatment cost, a proactive management approach may seem prudent.