See results in 6 hours with the Roundup 16 oz. Concentrate Plus Weed and Grass Killer. The fast acting concentrate kills grass and weed roots and can be used in and around fences, trees, driveways, flower beds and for lawn renovations. The 16 oz. container treats up to 1,500 sq. ft. and is rainproof in 30 minutes so it won't wash away.