Roundup, 1/2 Gallon, Concentrate Plus. Take control of your outdoor space with Roundup Weed and Grass Killer Concentrate. It kills tough weeds and grasses to the root, including dandelion, large crabgrass, poison ivy, clover (red and white), spotted spurge, and other broadleaf weeds. It is rainproof in as fast as 30 minutes, produces visible results in hours, and allows you to plant 1 to 30 days after application