Two species of crabgrass are widely spread throughout the United States: smooth crabgrass and hairy crabgrass. Both species were introduced from Eurasia. It grows in turfgrasses (usually smooth crabgrass--Digitaria ischaemum) and in ornamental landscapes (hairy crabgrass--D. sanguinalis). Crabgrass is also known as crowfoot grass or summer grass.
Create healthy turf that is dense and competes well with crabgrass, forcing it to move out. Dense turf also prevents crabgrass from establishing itself. Mow the turf at 2 1/2 to 3 inches in height. If you mow shorter, the crabgrass gets more sun and populations increase.
Water the lawn deeply once a week. If you water daily and do not give the lawn enough water at one time, you promote shallow root growth. Watering with an inch of water once a week allows the water to soak deeply into the soil, promoting deeper root growth and healthier turf.
Fertilize the yard with 2 to 4 lbs. of nitrogen per 1,000 square feet of lawn (once yearly in the spring). The fertilizer helps to create dense lawns. You can also apply about 60 percent nitrogen in September, then again in November after the final mowing. Do not use nitrogen-based fertilizer during the summer.
Spray the yard with preemergence herbicides in the early spring, preferably combined with the spring fertilizer. Preemergence herbicides kill crabgrass before it emerges. Common names of some preemergence herbicides include Oxadiazon and Pendimethalin.
Apply postemergence herbicides if you notice crabgrass in the yard and natural methods are not controlling the weed. Be sure to follow all instructions on the postemergence herbicide you choose, so you do not damage your turf. Postemergence herbicides include Monosodium methyl arsonate (MSMA), Dithiopyr and Fenoxaprop.