The dual-action formula of Roundup Ready-To-Use Extended Control Weed & Grass Killer Plus Weed Preventer II kills existing weeds down to the root and prevents new ones from growing for up to 4 months. 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. Rainproof in 10 minutes with visible results in 3 hours.