Roundup, a contact herbacide will not affect the shrubs unless you make contact with the spray. The chemical is not active in the soil. Period.
However, even Horsetail can withstand Roundup. They are not true plants, but a pre-historic fern and chemical makeup is much different and resistant too most herbacides. The problem is there are very few that WILL kill it. Your best bet would be to contact your local weed board and ask what you should use. Oregon State University suggests Casoron as a pre-emergant and MCPA for vegatative stages. However, it doesn't say whether available to homeowners or only licenced applicators.

Vera

Here is a link that might be useful: Oregon State U and Equistem arvense