Roundup Extended Control Weed and Grass Killer Plus Weed Preventer II Dual-action formula kills weeds to the root and pretreats weed prone areas such as driveways and sidewalks. Also ideal for use around patios, fences, foundations, curbs, retaining walls and lawn edge. Rain-proof in 10 minutes. Visible results in 3 hours. Prevents weeds from emerging for up to 4 months.