"David E. Ross" wrote:

If you really want to kill the ivy, apply Roundup to the foliage with a
sponge or brush, which will avoid damaging the tree on which it is
growing.

That's much too risky. The ivy will quickly draw the Roundup deep
into it's roots where it will be deposited in close proximity to the
tree roots, whereby it will severely damage if not kill the tree. I
strongly suggest removing the ivy roots mechanically (digging). In
most instances it's just not possible to eliminate established vines
without major excavation which will destroy desirable plants nearby as
well, then all one can do is constantly prune away what vines appear.
I constantly prune away all kinds of vines from hedgerows, forest
perimeters, and those that just pop up under trees/shrubs just sitting
out in a field... from seeds that birds drop... that how those vines
arrived at that plum tree, from birds eating vine berries and pooping
the seeds... there is no way to prevent that from reoccuring except by
removing that tree, which is precisely what applying Roundup nearby
will achieve... even is one is lucky enough to yank all those vines
brand new ones will soon appear... birds eat berries, perch in trees,
and poop... since the beginning of time.