Killing Bahiagrass in St. Augustine (Herbicide)
Established bahiagrass is difficult to remove from St. Augustinegrass without harming the lawn because the grasses do not have a dependable selective post-emergence treatment for this job. A label-approved, carefully directed nonselective herbicide can kill the patch, but it can also kill St. Augustinegrass it touches. Treat only the target, then repair the dead area with compatible turf.
A bahiagrass patch in a St. Augustine lawn can make a homeowner feel stuck: leave it and it may spread, or spray it and risk a bare spot. The practical answer is to protect the St. Augustinegrass, not to look for a “safe” spray that selectively removes established bahiagrass. The product label and careful application matter more than a broad lawn-treatment recipe.
In my maintenance approach, I first check that the grass has been identified correctly and mark where the bahiagrass ends. Then I choose a treatment method that keeps spray off the surrounding lawn. This guide explains how to make that decision, apply a product only as its label allows, and plan the repair.
What herbicide can remove bahiagrass from St. Augustine?
A nonselective herbicide can kill bahiagrass, but it may also kill St. Augustinegrass that it contacts. There is no dependable selective post-emergence herbicide for removing established bahiagrass while leaving St. Augustine unharmed. This makes targeted application and turf repair part of the same job.
Glyphosate is nonselective. If it reaches the St. Augustinegrass, the desirable turf may be injured or killed. Do not broadcast-spray glyphosate over a St. Augustine lawn, and do not assume a product is suitable just because it contains glyphosate. Check that its label permits the site and intended use, then follow its directions for rate, mixing, application, and protective equipment.
There is no universal glyphosate mix ratio. Products can differ in concentration and directions, so a rate from a different container may be wrong. Atrazine may suppress some bahiagrass growth or seedlings, but it is not dependable control for established patches. Use it only when the specific label permits the turf species, site, and intended application.
If you are unsure whether the patch is bahiagrass, confirm the identification before spraying. Grass species can look similar, and a mistaken identification can lead to needless injury. A local extension office can help with identification and region-specific guidance.
Key takeaway: For established patches, plan on careful, label-compliant spot treatment followed by repair, not a broadcast application or a promise of selective control.
Prepare the patch and equipment safely
Preparation means confirming the target, reading the entire product label, and setting up an applicator that can direct spray onto the bahiagrass alone. Check nearby plants, wind, drains, water, and label restrictions before mixing. Keep people and pets away as the label directs, and do not apply when spray could drift or run off.
Before opening the container, mark the patch boundary and note the area to be treated. A small patch close to healthy St. Augustinegrass calls for more precise placement than a broad, isolated area. If the grass is mixed tightly together, consider whether hand removal or another nonchemical option is safer than spraying.
Use equipment compatible with the product label. Depending on its directions, that may mean a suitable sprayer and nozzle or a directed applicator with a shield. Do not assume that a shield makes drift impossible. Keep the spray pattern controlled, and avoid treating beyond the target foliage.
| Check before treatment | What to do |
|---|---|
| Product and site | Confirm the label permits the site, turf setting, and intended target use. |
| Rate and mix | Use only the directions for that product and application. Do not borrow a rate from another formulation. |
| Applicator | Use the sprayer, nozzle, and method allowed by the label. Direct spray onto bahiagrass. |
| Weather and surroundings | Check wind and nearby plants, water, drains, and runoff paths. Follow all label limits. |
| People and pets | Follow the label’s protective equipment and re-entry instructions. |
Wear the protective equipment listed on the label. The rainfast interval, meaning the time needed before rain may affect the application, is product-specific. So is the restricted-entry interval, or REI, which sets when people may enter the treated area. Do not replace either with a general rule.
Key takeaway: Read the whole label before mixing. If the product or conditions do not fit its directions, do not apply it.
Apply herbicide as a directed spot treatment
A spot treatment means applying herbicide only to the identified patch, rather than spraying the whole lawn. Directing a label-approved nonselective product onto bahiagrass can reduce, but cannot remove, the risk to nearby St. Augustinegrass. The aim is controlled coverage of the target foliage with no overspray or runoff.
- Prepare the application. Confirm the product, rate, and method against its label. Calibrate the sprayer as directed so you can apply the intended amount. If you cannot control the spray close to the St. Augustine boundary, do not proceed with that setup.
- Choose suitable conditions. Do not spray when wind or other conditions could carry product onto desirable turf, nearby plants, or water. Avoid conditions that risk runoff. Follow any weather and application limits on the label.
- Treat the foliage. Direct the product onto bahiagrass only, using the label’s coverage directions. Do not spray past the marked boundary or apply more than directed. Repeat only if, and when, the label allows it.
- Record the work. Note the product, date, treated area, and conditions. Keep the label available so you can check the required follow-up and any limits on repeat or seasonal use.
A common failure is trying to make a treatment “more certain” by spraying heavily. That can increase exposure to the St. Augustine without proving the bahiagrass will be controlled. Follow the product’s stated rate and coverage; more is not a substitute for accuracy.
Key takeaway: Treat only when you can keep the spray on the target. If the patch is woven through the lawn, pause and seek local guidance rather than risking a larger injury.
Assess control and repair the lawn
After treatment, wait for the time and symptoms described on the label. Browning is evidence of injury, but it does not by itself prove that every part of the plant is dead. Check the patch for surviving crowns or new growth before you repair it, and retreat only if the label permits.
Once the treated grass is dead and the label permits, remove dead material if needed. Repair the opening with compatible St. Augustinegrass plugs or sod, then water and care for the repair according to its establishment needs and local guidance. Match the grass type to the existing lawn where practical.
Do not rush the repair while live bahiagrass remains in the opening. New turf can be crowded by regrowth, leaving you with the same problem and another repair. On the other hand, leaving bare soil open can create space for unwanted plants. Check the area as the treatment develops, then make the repair when it is appropriate under the label.
Clean the applicator and manage rinsate and containers exactly as the product label and local rules direct. Do not reuse herbicide equipment for irrigation or other purposes. Store the product in its original labeled container, secured from children and pets, and follow label directions for storage, including protection from heat or freezing.
Key takeaway: Judge control by follow-up inspection, not color alone. Repair only after the treatment and label directions allow it.
Practical treatment scenarios
These are decision examples, not claims about a specific property or product. They show how patch size, proximity to healthy turf, and identification affect the next step. In each case, the label and local conditions still control whether an herbicide application is allowed.
A small, distinct patch in open turf: Confirm the grass, mark its edge, and check the label. If an approved product and directed applicator can keep spray on the bahiagrass, a spot treatment may be practical. Inspect later for regrowth, then repair the area when appropriate.
A patch mixed through St. Augustinegrass: Spraying is harder to control when the grasses overlap. A shield may help limit spray movement, but it does not make contact harmless. If you cannot isolate the target, stop and ask a local extension professional about identification and options.
A larger area near a bed, drain, or water: Check label restrictions and the risk of drift or runoff before deciding on any treatment. Nearby plants and water can change what is allowed or prudent. Do not apply just because the grass is easy to reach.
A patch that browns, then returns: Look for surviving crowns or fresh growth and review the product’s directions before considering another application. A repeat treatment is not automatic. Confirm that the label allows it and that the conditions are suitable.
Key takeaway: The safest choice depends on whether you can identify and isolate the target, not just on how much grass is present.
Prevent reinvasion and keep useful records
Follow-up means checking the treated area, maintaining a dense lawn, and keeping a record of each application. A healthy, established St. Augustine lawn leaves less bare soil for unwanted grass to occupy. Avoid scalping, and look for site conditions that leave thin or open areas instead of treating every new shoot without diagnosis.
Inspect the repair and nearby turf for surviving bahiagrass or seedlings. If growth returns, identify it before acting and follow the label for any additional treatment. Record the product, date, treated area, weather, and next check. These notes help you avoid accidental repeat applications that exceed label limits.
Store herbicide only as its label directs, in its original container with the label intact. Keep it secured from children and pets. Observe limits on annual applications and seasonal use, and follow local rules for disposal.
Key takeaway: A small follow-up check can catch regrowth early. Dense turf, careful repair, and accurate records reduce repeat work.
Frequently asked questions
Can I kill bahiagrass without harming St. Augustinegrass?
There is no dependable selective post-emergence herbicide for established bahiagrass in St. Augustinegrass. A nonselective product can injure or kill either grass it contacts, so targeted application and repair are important.
Will glyphosate kill St. Augustinegrass?
Yes. Glyphosate is nonselective and can injure or kill St. Augustinegrass if it contacts the foliage. Do not broadcast-spray it over a St. Augustine lawn.
What glyphosate rate should I use?
There is no universal rate or mix ratio. Follow the directions for the exact product, formulation, site, and application method. If the label does not allow the intended use, do not apply it.
Can atrazine remove an established bahiagrass patch?
Atrazine may suppress some bahiagrass growth or seedlings, but it is not dependable control for established patches. Use it only if the specific label permits the site, turf species, and intended application.
Can I spray when rain is expected?
Check the product’s label for its rainfast interval and weather limits. These vary by product. Do not use a generic waiting period in place of the label.
When can people and pets return to the lawn?
Follow the label’s re-entry instructions. The required interval is product-specific, so do not rely on a general estimate.
Should I repeat the application if the patch is still green?
Not automatically. Allow the label-directed time for symptoms and control, then inspect for surviving growth. Repeat only if the label allows it and its directions are met.
When should I plug or sod the treated area?
Wait until the bahiagrass is dead and the label permits repair. Then use compatible St. Augustinegrass and follow establishment guidance for watering and care.
What if spray reaches St. Augustinegrass?
Glyphosate can injure or kill turf it contacts. Follow the product label for any exposure guidance, then monitor the area. Avoid further applications until you have checked the label and assessed the damage.
How do I dispose of leftover spray or containers?
Follow the product label and local rules for rinsate and container disposal. Do not pour leftover product into a drain or reuse herbicide equipment for another purpose.
The reliable plan is straightforward: identify the grass, choose only a label-approved product and method, direct treatment onto bahiagrass, and inspect before repairing. Because the treatment can damage St. Augustinegrass, control depends on careful placement and follow-up, not on a blanket spray.
(This article was written by one of our staff writers, Victor Dempsey. Visit our Meet the Team page.)
