Crabgrass is an annual grassy weed that sets seed and dies in the autumn of each year, and often is found in lawns that have poorly maintained soil and turf, according to the Cornell Cooperative Extension. Crabgrass weed begins germinating when the soil is 60 degrees F for three to four days at the quarter-inch level of topsoil. It spreads seeds in July before dying off in the fall. Early cultivation and chemical control of the weed is essential to prevent new crabgrass in the next year.
Mow the lawn to a height of 2-1/2 to 3 inches, never removing more than one-third of the blade at a time.
Water the lawn to wet the soil to the depth of rooting, which depends on the main grass variety in the lawn. In turf grass, the lawn will turn bluish gray and footprints will appear when walked on if not watered enough.
Apply 2 to 4 lbs. of fertilizer per 1,000 square feet per year, once in September and again in November. Avoid applying nitrogen fertilizer to the lawn during the summer as this makes crabgrass more resistant to control.
Apply a pre-emergent herbicide such as bensulide or pendimethalin around the last three weeks of April or the beginning of March to kill crabgrass seed. Apply according to the directions on the label.
Spray a post-emergent herbicide such as MSMA or quinclorac to crabgrass on rain-free, no-wind days. Apply directly to the crabgrass area to prevent spraying desirable plants.