Roundup Extended Control Weed and Grass Killer Plus Weed Preventer II Ready-to-Use Comfort Wand Sprayer, 1.33-Gallon Dual-action formula kills existing weeds and prevents new ones from growing for up to 4 months Kills weeds to the root. Guaranteed! Use on driveways, sidewalks, and patios; along fences, foundations, curbs, retaining walls and edge of lawns, as well as on decorative rock or gravel areas Rainproof in 10 minutes Visible results in 3 hours