2009.08.08: Austria, Vienna XXII. district, 155 m AMSL, growing on badly damaged Populus nigra.
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 P. nigra won't last very long, probably a couple of years.
Both species are common.
German name: Laubholz-Mistel.