The effect of a biocontrol fungus Chondrostereum purpureum on sprouting of rowan (Sorbus aucuparia) at different application times

In Southern Finland, rowan (Sorbus aucuparia L.) forms local thickets in young forests where it competes with more valuable conifers. Therefore, these thickets are regularly cut to provide more growing space for conifers. This has been inefficient at preventing excessive sprouting and therefore, new alternatives have been investigated. One of the potential options is to utilize a decay fungus Chondrostereum purpureum (Pers. ex Fr.) Pouzar for controlling sprouting. Spreading mycelia of this fungal species on freshly cut stumps starts a decay process in exposed wood and thus prevents sprouting. In this study, the ability of rowan to sprout after the fungal treatment was investigated at different application times from early spring to late autumn. Three years after the treatment, stump mortality was highest (ca. 40%) among stumps treated in summer and lowest in stumps treated in early spring or late autumn (ca. 20%). Furthermore, sprouts were significantly reduced in stumps treated in summer than in early spring or late autumn. The results indicate that rowan is capable of tolerating fungal infection better in early spring and late autumn than in summer, possibly because in early spring and late autumn resources available for regrowth are in belowground parts of a tree, unlike in summer when nutrients are transported within the stem to leaves and inflorescences. Thus, in rowan, the best sprout control efficacy can be achieved when performed in summer.