Cuttings of Populus hybrid clone NE-388 (Populusmaximowiczii Henry × Populustrichocarpa Torr & Gray) were inoculated with mycelium of Septoriamusiva Peck at three potential infection courts. Cankers resulting from inoculations at stipule – petiole excision wounds and bud excision wounds developed within 17–30 and 18–22 days, respectively. Only one canker resulted from 30 nonwound lenticel inoculations. Young trees (15 and 16 weeks from planting date) developed more cankers than older trees (18 weeks from planting date). Trees atomized with conidia of S. musiva did not develop cankers; however, leaf spots developed 18–23 days after inoculation.