Evaluating the Pathogenicity of Chondrostereum purpureum and Fungi Obtained from Dying Buckthorn on Common and Glossy Buckthorn

Common buckthorn (Rhamnus cathartica) and glossy buckthorn (Frangula alnus) are large shrubs that are invasive to Eastern North America. Currently available removal techniques, such as uprooting and systemic herbicides, can be too laborious to conduct over broad acreage or have the potential to cause harm to non-target organisms. A mycoherbicide to control buckthorn would provide a new management tool. In greenhouse experiments, we screened 44 putatively pathogenic fungi that were acquired from a collection of fungi derived from dying buckthorn in Minnesota and Wisconsin. Ten of these fungi caused cankers when inoculated into the stems of common buckthorn saplings, including: Cylindrobasidium evolvens, Fusarium sambucinum, F. sporotrichioides, F. graminearum, F. brachygibbosum, Mycoleptodiscus terrestris, Neocucurbitaria rhamni, Pezicula frangulae subsp. frangulae, Ramularia robusta, and Xylaria polymorpha. In field experiments, three of these fungi, F. sambucinum, F. sporotrichioides, and P. frangulae subsp. frangulae, plus a local isolate of Chondrostereum purpureum, caused cankers on both glossy buckthorn and common buckthorn stems. In an additional field study, 90% and 100% of common buckthorn stumps inoculated with C. purpureum were dead after 12 and 23 months, respectively. Future research should focus on developing a scalable and effective method for applying fungi as mycoherbicides to buckthorn.