Roundup For Lawns kills the toughest weeds down to the root. For fast control on tough weeds like dollarweed dandelion clover and yellow nutsedge. It can be used on Southern grasses including Centipede St. Augustine and Floratam. Roundup For Lawns is a tough weed killer for use on Southern grasses that kills weeds not the lawn (when used as directed). Rainproof in 4 hours. Roundup For Lawns kills the root so weeds won’t come back. The best time for broadleaf weed applications is when weeds are young actively growing and soil moisture is adequate. Weeds typically twist curl or yellow within a few days of application while weed death can occur within 14 to 28 days. Roundup For Lawns is a simple step for home lawn care. No weeds. No worry.