A lawn infiltrated with invasive and unwanted grasses is usually very frustrating. This is typically true of Bermuda grass that grows in a St. Augustine grass lawn. Fortunately, a few strong herbicides aree specifically formulated for killing Bermuda grass. Selecting the one appropriate for you depends on personal choice and your budget. Follow safety procedures when using these herbicides, especially if you have children or pets.
Walk through your lawn to determine where Bermuda grass is present. This grass is finer in texture than St. Augustine grass and does not tolerate shady spots well, which is why it grows in direct sun. Check whether the grass grows in patches along with your St. Augustine lawn grass, or is mixed throughout.
Mow your lawn as tall as the mower allows so St. Augustine grass shades Bermuda grass, which the Bermuda grass cannot tolerate. Mow your grass to your desired height after several weeks, once Bermuda grass dies of overcrowding.
Fill a spray pump with a liquid herbicide specifically formulated for killing Bermuda lawn grass. Check the product to make sure it lists the grasses it kills and does not kill. Follow the manufacturer's directions for pouring it in concentrated form or diluting it.
Spray the herbicide directly over obvious patches of Bermuda grass, or over the entire lawn if it is mixed in with St. Augustine grass. Spray an infested spot evenly so you cover it completely.
Pull the dead grass by hand, or rake large patches. Collect in a garbage bag and dispose.