Yes roundup can be used within a couple inches of the trunks of shrubs. Use extreme caution and use as little product as possible to get the job done. Do it when the wind is calm.
Bill Hill

A trick I learned to reduce drift is I took a gallon milk jug and cut off the bottom. Then I stuck the end of the wand of my sprayer into the top and taped it. That way you can completely surround the weed with the milk jug and spray the daylights out of it without worrying about drift.

There are also products out there that will kill grassy weeds without harming most ornamentals. The most popular is fusilade. It is under many trade names and found in garden centers and such. Look for the active ingredient fluazifop-p-butyl.

Good idea denverdude. Might try that one. I've wiped out more than one shrub by spraying RU. Seemed like every time I got out there to spray the wind would come up...was still as could be before. Geeeshhh!!!