Crabgrass is a particularly invasive type of grass. It can overpower any and all other grasses in your yard, including Bermuda grass, smothering them and completely covering a lawn in a single season. Young crabgrass plants are easier to kill than older, well-established clumps. Unless you want to patiently dig up every bit of crabgrass on your lawn (and are prepared to start digging all over again as soon as you've finished), then the best way to kill crabgrass in a Bermuda lawn is by using a very selective weed killer.
Purchase a tank-type sprayer. A 2-gallon sprayer should be large enough for most home weed problems.
Buy a weed killer that is specifically designed to kill crabgrass. Many such weed killers contain quinclorac, although this is not the only weed killer that specifically kills crabgrass. Read the label to make certain that you are purchasing a crabgrass-selective weed killer and not a nonselective weed killer. A crabgrass-selective weed killer is harmless to Bermuda grass, unless the average temperature each day is above 90 degrees Fahrenheit, which weakens Bermuda grass.
Water your lawn thoroughly to encourage the growth of any crabgrass. Put at least 1 inch of water on your lawn. Wait 24 hours after watering to apply your crabgrass herbicide.
Choose a nonwindy day when the temperature is lower than 90 degrees Fahrenheit and when rain is not predicted for at least 24 hours. Wear gloves and a breathing mask when mixing your herbicide. Mix your crabgrass-selective herbicide in your tank sprayer at the concentration recommended by the manufacturer. Do not mix a stronger concentration.
Spray your yard thoroughly, making certain that the leaves of all of the crabgrass are thoroughly soaked by the spray. Again, wear gloves and a breathing mask when spraying. Do not worry about any spray that lands on your Bermuda grass, as a crabgrass-selective herbicide will not harm it, provided that temperatures are below 90 degrees Fahrenheit.
Water your lawn thoroughly after the herbicide has had at least 24 hours to work its way through the leaves and into the roots. Keep your lawn damp, but not soaking wet, for seven days. Then, spray your yard a second time with the crabgrass-selective herbicide, mixing it per the manufacturer's instructions. Do not spray a third time during the same growing season.