Roundup Dual Action Weed & Grass Killer + 4 Month Preventer 1 GAL RTU Trigger. Dual Action formula kills existing weeds & prevents landscape and hardscape weeds from growing. Spray directly to kill weeds and grass down to the roots. Spray in weed prone areas to create an invisible weed barrier for up to 4 months. Use in driveways, sidewalks, and patios; along fences, foundations, curbs, retaining walls, and edge lawns; as well as on decorative rock or gravel areas.