Experts and BHG readers answer.
Thanks for writing. At this point, the only really good way of dealing with the crabgrass you have is to pull it out by hand. There really aren't any herbicides that will affect crabgrass but not lawn grasses.
On the bright side, though, crabgrass is an annual weed. So you can use a pre-emergence herbicide several times in early spring to stop most of the crabgrass seeds from ever sprouting. The ideal time to use many of these crabgrass preventers is about the time forysthia shrubs bloom in your area. Check the instructions on the packaging to know how much and how often to reapply the product.
---Justin, Senior Garden Editor, BHG.com