In 2006, a new canker was observed on trees of Populus × euramericana '74/76' and P. × euramericana 'Zhonglin 46' in the Henan and Shandong provinces of China. The disease, which is characterized by canker with white exudates dripping from the bark, occurred mainly in the summer. A particular gram-negative, rod-shaped bacterium was repeatedly isolated from the infected samples and proven to infect trees of P. × euramericana by Koch's postulates. Through a polyphasic taxonomic approach using sequence, DNA-DNA hybridization, chemotaxonomic, and phenotypic data, the poplar isolates were identified as Lonsdalea quercina subsp. populi, a subspecies very recently described based on isolates from oozing bark canker of poplar (P. × euramericana) trees in Hungary.