Stop two of the most common yet aggravating weeds pesky dandelion and large crabgrass weeds before they start with SCOTTS TURF BUILDER WEED PREVENT CORN GLUTEN MEAL. Contains 100% corn gluten meal, a natural, pre-emergent weed seed preventer. For best results, apply before weeds appear, usually in early Spring and again in late Summer or early fall. Ideal for established perennial ryegrass and Kentucky bluegrass lawns. Not for use on newly seeded lawns or when over-seeding or re-sodding.