How To Kill Weeds in St. Augustine Grass

Can you kill weeds in St. Augustine grass without killing the grass?  Do you have weeds in your St. Augustine grass lawn?  In this video, Houston Grass Owner Michael Romine talks about how to kill weeds in St. Augustine grass without damaging your lawn. Call us at 281-431-7441 for grass sod with quality second to none in the Houston area, and at very competitive prices too.

Summary of How to Kill Weeds in St. Augustine Grass

Since this video was recorded, we’ve updated our recommendations for using herbicides to kill weeds in your lawn.  You can download our Established Grass Tip Sheet to print a copy.  The Tip Sheet care instructions are what we currently recommend and the following recommendations on the use of herbicides are from our Tip Sheet. 

Herbicides – never apply on grass less than one year old

  • January – March — Suggest mowing when winter weeds appear as opposed to treating with chemicals. Apply Nitro-Phos Barricade Pre-emergent herbicide in February.
  • April — If a weed and feed is needed for a St. Augustine lawn, we recommend Nitro-Phos 15-5-10 with Atrazine. We do not recommend that you use Atrazine repeatedly on your lawn. If a weed and feed is needed for a Bermuda, Zoysia or St. Augustine lawn, we recommend Nitro-Phos 15-5-10 with Trimec. CAUTION: these chemicals will kill plants & ornamental flowers, be careful when applying! Do not apply weed and feeds with Atrazine to Bermuda grass or Zoysia grass lawns.
  • May – September — Nitro-Phos Barricade Pre-emergent herbicide in May.
  • October – November — Nitro-Phos Barricade Pre-emergent herbicide.
  • December — Suggest mowing when winter weeds appear as opposed to treating with chemicals.

Transcription of the “How to Kill Weeds in St. Augustine Grass” Video

How to kill weeds in St. Augustine? There are lots of different kinds of weeds. Some easier to kill than others.

Going into springtime you get lots of clovers. We just classify them as the winter weeds and in my own yard, I put out Scotts Bonus S. It’s a fertilizer that’s been impregnated with a chemical that is a fairly, good weed killer as well and if you put that out there, just like you do fertilizer, follow the directions on the bag and you put it out with your push fertilizer spreader. That is one way to clean up a lot of the winter weeds.  I now use and recommend Nitro-Phos Weed & Feed with Atrazine to control broadleaf weeds in St. Augustine grass.

You get into some of the hardier weeds,  pre-emergent herbicide I guess is probably the best way to control weeds. You put that out right before we go into springtime, right before the temperature warms up. Most of those pre-emergent herbicides are controlled and you have to have a chemical applicators’ license to apply them.  So a TruGreen, or a Greenup or somebody with a chemical applicator’s license has to come out and put those out.  I now recommend  Nitro-Phos Barricade Pre-Emergent Herbicide.

Basically, they put those chemicals out in a liquid form and they form a barrier on top of the soil.  Then any seeds of weeds already there or landing there they can’t germinate because of this layer of pre-emergent herbicide. When weeds never exist obviously is the easiest thing.

The Atrazine impregnated fertilizer can be used for St. Augustine in the springtime (we carry Nitro Phos St. Augustine Weed & Feed w/Atrazine 15-5-10).  For the hardier weeds like Dallas Grass, Roundup weed killer is usually the only thing that can do the job, especially once the weeds get very mature.

You can use Roundup with just spot spraying. Roundup is a non-selective herbicide, meaning anything it touches it kills. So you would want to apply something like that on a day that’s not windy at all.  A hotter day is better than a cool day because the weed will soak up the Roundup better on a hot day.

Killing Bermuda Grass in St. Augustine Is Hard

The biggest problem in St. Augustine is Bermuda grass. If you’ve got Bermuda grass in St. Augustine, there is no selective herbicide that will kill Bermuda grass out of your St. Augustine, without killing the St. Augustine. So when you have Bermuda grass in your St. Augustine grass and it bothers you that you’ve got a mix of grasses out there, the only way to get rid of it is to get Roundup and follow the directions on the packaging.

We provide that service as well.  We use Roundup to spray every square inch of the area you’re trying to get rid of and wait about ten days for the weeds to die.  Then we come in with either a weed eater or sod cutter, cut that area out, haul that off and then plant the new St. Augustine.

It’s a very laborious task and an expensive task to do well, but it is unfortunately the only way to really clean the Bermuda Grass out of your St. Augustine. If you neglect to spray that Bermuda grass with Roundup before you take it out with that sod cutter, the Bermuda grass roots would stay in the soil.  In six months to a year, the Bermuda grass is going to reappear from those remaining roots even if you totally clean the Bermuda grass above ground. So Bermuda grass is a tough one to get rid of but we’ve had lots of success with doing it by that method.

Texas A&M has a world-class turfgrass research program and that Aggie Turfgrass website has extensive information to help you identify the weeds and the insects that may impact your Texas lawn.  Please check this website for in-depth information about weeds and lawn insects.

Houston Grass Can Help You Kill Weeds in St. Augustine Grass

Houston Grass has the proven Nitro-Phos products you need to prevent weeds from emerging in your lawn in the springtime and kill any weeds that do take root.  We also deliver high quality grass sod grown on the family farm in Bay City, TX.  We’re located just off Highway 6, on McKeever Road in Arcola, and we’re just a few miles east of Sienna Plantation.

You can pick up your grass at our office or we can deliver it to your project site.  We can also arrange for installation services.

You can pick up your grass sod at our office or we can arrange delivery.  Please contact us at 281-431-7441 for more information and a quote for your sod.