A: The chemical we know as 2,4-D may be “smart” enough to tell the difference between a grassy plant and a broadleafed plant but it can’t tell the difference between vinca and vetch. All weedkillers that are labeled for control of broadleafed weeds like dandelion, clover and chickweed will ruthlessly kill ornamental plants as well. There are a few exceptions but these chemicals are difficult to find and use. Wait for a warm day to get out and pull up all of the vetch. To control vetch and chickweed, consider using a broadleaf weed preventer in September each year.