Crabgrass Treatment for a New Lawn

Preemergents

• Never use most preemergent herbicides when planting your lawn. They provide excellent control for crabgrass, when timed correctly, but also prevent lawn seeds from germinating. Their effects may last from five weeks to six months, depending on the herbicide. The exception is siduron, a preemergent safe for new fescue and bluegrass lawns.

Postemergents

• Don't apply granular postemergent crabgrass killers until your new lawn grows strong enough to metabolize the herbicide. A rule-of-thumb is to wait until you have mowed the lawn at least two to three times. Until then, spot-treat crabgrass with a wide-spectrum herbicide. Repeat treatment to crabgrass plants with three or more branches.

Timing

• Crabgrass is a warm-season annual, while most lawn grasses are cool-season perennials. This means that fall planting is ideal for fescue and bluegrass lawns. The cool temperatures prevent crabgrass from gaining a strong foothold and keep young, tender lawns out of summer's heat. For extra control, treat your lawn bed with a preemergent in early spring, allowing time for the herbicide to dissipate before fall planting.