2009.08.08: Austria, Vienna XXII. district, 155 m AMSL, growing on badly damaged Populus sp.(near creek - Hausgraben
). Of course mistletoe isn't the main or primary reason for trees dying but they help the process along. My guess would be that this poplar won't last very long, probably a couple of years. The tree could be either Populus nigra or one of its hybrids, P. × canescens and - as suggested below by Sciadopitys - P. × canadensis, especially as it is
true that the hybrid P. × canadensis is particularly often host of Viscum - however, I've also seen plenty of P. nigra bearing V. album. Both species are common. German name: Laubholz-Mistel.