The dual-action formula of Roundup Ready-To-Use Extended Control Weed & Grass Killer Plus Weed Preventer II refill kills existing weeds and prevents new ones from growing for up to 4 months and it kills them down to the root. Plus the Roundup Extended Control can be used on driveways sidewalks patios along fences curbs retaining walls and edges of lawns as well as on decorative rock or gravel areas. This is the easy and ecoNomical way to refill any Roundup Extended Control Ready-to-Use applicator.