Fast acting weed and grass killer formula kill weeds and unwanted grasses, with results you can start to see in 15 minutes. This weed killer controls weeds like chickweed, algae, dandelion, ragweed, shepherd's purse, moss, mustards, oxalis, and others (as listed). It also controls grasses including crabgrass (large), bluegrass (annual), onion (wild), and perennial ryegrass. Apply this landscape weed control at any time of the year when weeds are small (3 In. tall or wide) and actively growing. Treatments can be made to walkways, driveways, landscape beds, and under trees. Weeds will turn from green to brown within 1 to 2 hours.