Crabgrass can be effectively controlled with post-emergence crabgrass herbicides. These herbicides can safely be spread on your lawn without harming most grass varieties, but be careful to read the label to make sure that the herbicide is listed as safe to use on the variety of grass in your lawn. Once this season's crabgrass has been killed by herbicide treatment, the best defense against repeated infestation is a thick-growing, well-cared-for lawn.
Water your lawn with two inches of water the day before you apply the herbicide. You should never chemically treat a drought-stressed lawn.
Spray your lawn with post-emergent crabgrass herbicide according to the manufacturer's instructions for application rates and methods. Different herbicides require different application methods (usually hose-end sprayers, pump sprayers or hand-held sprayers). Most require you to thoroughly coat the lawn with herbicide just before the point of run-off.
Refrain from watering or mowing your lawn for 24 hours after treating it with herbicide.
Re-spray the crabgrass if needed at the intervals dictated by the herbicide's manufacturer (usually within one week).