Invasive vine on boxwoods

I have a big, beautiful 70-year-old boxwood hedge. The only problem is that an invasive vine keeps growing up over the bushes. This vine has the tinsel strength of steel cable and seems to grow about 3 feet a night. Looks a little like wild clematis and behaves like kudzu. I’ve pulled it off the bushes and sprayed the base with round-up, but it comes back. I’ve also mulched the base of the boxwoods. Is there any “over the top” weed killer that is safe to use? Any suggestions before it starts again this spring?

I was attracted by your name. My grandmother was a Cherokee Indian and was born in Oklahoma. Her name was Hattie Bell and I have never seen any one with that name before. Her last name was Augerhole. I can't id your vine but good luck. Some one will come along and do that for you. Elaine

Then you might be interested to know there is a japanese morning glory named "Hattie Bell".
http://davesgarden.com/guides/pf/go/69512/

It might help if you could get a picture of the vine--some plants respond better to herbicides than others, so without knowing what you have it's hard to make a recommendation. Anything that will kill the vine will also kill your boxwood though, so you'll need to go at it with a paintbrush or something so you don't get anything on the boxwood leaves. If the vine's coming up every year from seed then you could use corn gluten or another pre-emergent to keep it from germinating (and that won't hurt the boxwood) but if it's coming back from its roots every year then that won't do any good.

it sounds like field bindweed. does it have arrowhead shaped leaves? they get flowers for a short time i think in the spring.

Could be bindweed. Certainly can bind up some big boxwoods. Pre-emergent won't work, I guess, because the vine isn't from seed. So much for easy. Will try to catch it early (again), but most likely I'll be posting vine photos by mid-summer. Thanks for the info