AbstractCeratocystis fimbriata, the cause of “target canker” in aspen,Populus trenuloidesMichx. In North America, is reported associated with similar cankers on some poplar hybrids (Papulus maximowiczii × P. x. berolinensis) of the so‐called “black balsam” group (Aigeiros × Tacamaliaca) in Poland.A short description of disease symptoms and the peritheeial and conidial stages of the fungus is given.The presence of bacterial canker caused byAplanobacter populiRidé has not been demonstrated in Poland by isolation from nat