First Report of a Powdery Mildew‐like Disease caused by <i>Teratoramularia rumicicola</i> on <scp> <i>Rumex obtusifolius</i> </scp> in Korea

ABSTRACT Rumex obtusifolius , a perennial plant native to Europe, has become an aggressive invasive weed across temperate regions worldwide. Rumex obtusifolius poses a significant threat to agricultural ecosystems, highlighting the need for effective management strategies. During the summer of 2022, powdery mildew‐like symptoms were observed on the leaves of R. obtusifolius at four locations in Korea. The causal agent was identified as Teratoramularia rumicicola through morphological characterization and phylogenetic analysis based on the ITS and LSU genes of the rDNA. Artificial inoculation of healthy R. obtusifolius leaves with an isolate obtained from this pathogen led to symptom development after 6 days, thereby fulfilling Koch's postulates. This study is the first global report of R. obtusifolius infected with T. rumicicola .