Preen Lawn Crabgrass Preventer prevents crabgrass and other grassy and broadleaf weeds for up to 4 months when applied prior to their germination in lawns and ornamental turfgrasses. It also provides post-emergence control of seedlings crabgrass for up to 4 weeks after it germinates. Don"t choose between killing and preventing - get both! Preen Lawn Crabgrass Preventer provides season-long control for some of the toughest weeds including crabgrass, bluegrass, chickweed, henbit, yellow foxtail and spurge. Use it on many types of cool and warm season grasses like Bentgrass, Fescues, Kentucky Bluegrass, Ryegrass, Bermudagrass, Carpetgrass, St. Augustinegrass and Zoysiagrass. Preen Lawn Crabgrass Preventer should be applied to lawns and ornamental turfgrasses that are well-established. When used according to the directions, it will not harm nearby established ornamentals. 17 lb bag.