A day or two after a good rain is an excellent time to apply herbicides to the lawn to kill weeds.
One of our most despised weeds in the lawn is bahia grass. If given adequate moisture, bahia shoots up its ugly seed heads in only two or three days, making us have to mow the lawn more often than we wish.
If you know what bahia looks like in your lawn without seeing the seed heads, you should start controlling it as soon as possible.
Selective herbicides suppress the bahia in order to allow your desirable grass to take over.
By far the best herbicide for controlling bahia is a product containing metsulfuron. In the past this was sold strictly as highly concentrated, commercial products Manor or Blade, packaged in a small container that cost around $140. Fortunately the price has dropped. You can now find it in a few stores in the Augusta area in a 2-oz. size in the $50-$65 range. A 2-oz. bottle will treat approximately 4 acres. A couple of brand names are MSM and Mansion.
The great thing about metsulfuron is that it is safe for all four of our warm season grasses (centipede, zoysia, Bermuda and St. Augustine). Metsulfuron is also good for controlling other weeds, including one of our hardest-to-kill weeds, Virginia buttonweed.
Another herbicide that works pretty well on bahia, imazaquin (sold as Image), can also be used on all four of our lawn grasses. When using Image this time of year, you should make a second application in about six weeks. An immediate benefit you get from this herbicide is that even though it might not completely kill the bahia after the first application, it will prevent any seed heads from popping up for several weeks. Half the battle is then won.
If you have a centipede lawn, sethoxydim (sold as Poast, Vantage, Segment, or Post-Emergence Grass Killer, Over the Top Grassy Weed Killer) should be your second or third choice for control. Sethoxydim is rated fair in control of bahia. This product can be used only on centipede as it kills or suppresses all other grasses including crabgrass and Bermuda. If you have other undesirable lawn grasses in centipede, you can take them out with sethoxydim.
One final herbicide option to consider is spot treating with glyphosate (Roundup) or some similar nonselective herbicide. Naturally, this would kill your desirable grass if you got any on it, but you might be willing to deal with the dead spots while your permanent grass grows back in.
If you do not like to use herbicides or if you just have a few small areas, you can just dig up the bahia.