Larry,
Unfortunately, there is not a magical herbicide you can apply to prevent BOTH grass and broadleaf weed germination without harming young seedlings or your money crop, ginseng. Ginseng is classified as a broadleaf and therefore is susceptible to any pre-emergent or post-emergent broadleaf herbicide. If you want to use an herbicide program, then you will have to apply herbicides prior to establishing your ginseng patch.
Sorry, manual weed removal is your only "guaranteed" option for controlling grass and broadleaves in a woods-grown ginseng patch.
Jay