We have the same problem. We hand weed them as some as they creep out. It is on a steep hill so is a pain but what do you do!!!

Is that area well mulched?

What can be sprayed on that will kill the crap growing and not harm the junipers ?? We tried Preen this year and it is like the Preen was just seeds !!! Now it is worse than ever.

Bump

You don't specify what weeds you have but if you haven't done so yet, you should have them correctly identified before you try any herbicide on them. You won't know their life cycles and weak points until you get them identified.

Are they crawling all over the junipers - touching them - or growing straight up like a grass?

One method for weeds growing above grouncovers is to use the "glove of death". Put a rubber glove on your hand and put a cotton glove over it. Then dip your hand in the herbicide solution (in liquid form) and lovingly caress the weeds to death. This works great for grasses and other upright weeds, but would be tricky for vining, crawling ones.

Sometimes with the vining ones(like bindweed)you can place bamboo posts in the beds and trick the vines to grow around the posts. Then use your glove and run your hand up the posts.

It's important to follow label rates on your herbicide. More is not better and puts more chemicals into the environment than necessary to kill off your target. Sometimes a stronger solution actually burns the plants back so fast that the herbicide does not have time to work its way throughout the root system.

Good luck and I hope this helps.