6 Best Pre Emergent Weed Killers For St. Augustine & When To Apply

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Jun 20, 2023

Around the globe, landscapes with moderate climates are often covered with St. Augustine lawns. This broad-leaved grass is highly prized for its propensity to flourish in various soil conditions, including full sun, shade, and both. It’s not impenetrable, however. Especially while fighting weeds.

The most prevalent weed species on this grass thrive in comparable conditions. For many St. Augustine lawn aficionados, chickweed, henbit, clover, and dollar weed have been the devil’s advocate for ages. The urge to get rid of them follows. I’ve done all the work to save you from going through several pages of reviews and purchasing something that doesn’t function. My list of the top six pre-emergent weed killers for St. Augustine grass has been trimmed down after many testing seasons.

Among the Best Pre-Emergency Weed Killers For St. Augustine

Here are my suggestions for granular and liquid pre-emergents if you’re in a hurry. They are professional-grade items that will satisfy you and regularly deliver a strong performance.

Best For Broadcasting

The Andersons Barricade

Pre-emergent granular of expert grade. With any broadcaster or spreader ready to use. s 5,800 square feet

Best Pre-Emergent Spray

Quali-Pro Prodiamine

Pre-emergent that is very effective and water-soluble, made for herbicide sprayers. s 48,000 square feet

How To Choose Pre-Emergent For St. Augustine Lawns

So what features does the finest pre-emergent possess? How does it work? Well, it depends on several variables. Are you attempting to eradicate current weeds, prevent new ones from sprouting, or both? What degree of infection is there? Either there aren’t many, or there are many of them.

Some that I examined use active substances to eradicate weeds at the seedling stage. Others destroy weeds at the cellular level to stop their development after the seeds have sprouted. Meanwhile, they are designed to eliminate weeds without damaging your lawn.

Common Weeds In St. Augustine Grass

As previously indicated, several weed species are often strewn across St. Augustine grass. Each plant has a distinctive appearance, with some having broad-leafed structures and others being grassy. However, they all disembark similarly, scattering their seeds toward your manicured grass. Let’s examine a few of them:

Broadleaf Weeds

Due to the stark differences between broadleaf weeds and healthy grass structures, they are simple to recognize. Rapidly succeeding single or clustered blooms release hundreds of seeds at once. The appropriate pre-emergent will suppress these common kinds.


This winter annual forms clumps and has a single, central stem with several flat, broad leaves growing along it. The color of this weed is significantly lighter than St. Augustine grass. It also produces tiny, white blossoms between March and November that quickly develop into unfavorable seeds.


Each form of this plant has low-growing flowers with a recognizable three-petal shape and blooms from early spring to late autumn. Its shallow root structure makes it simpler to get rid of inside the grass. It is hence often planted as a ground cover in controlled environments.

Dollar Weed

This common plant, also known as pennywort, is a warm-season perennial and is distinguishable by its “silver dollar”-shaped leaves. Dollar weed grows in soil that doesn’t drain well, has too much moisture, and has shallow-rooted lawns.

Grassy Weeds

These grassy annuals also grow in clusters like the broadleaf type, but their blades are solitary and arise from a central crown. They often throw forth either yellow or white multi-petaled blooms after the life cycle’s conclusion, a profusion of seeds.

Bermuda Grass

Bermuda grass seeds may invade other lawns and swiftly take over, despite being often cultivated as landscaping turf. Although Bermuda grass can withstand extreme heat and dryness, some people want a uniform spread of one particular variety of grass, in which case a herbicide may be necessary for Bermuda grass.


On the other side, crabgrass does nothing for the health of your lawn. Clumps that proliferate make your grass compete with them for water and nutrients and give your green landscape a blotchy look. The easiest way to avoid this is to remove crabgrass as soon as it emerges.

Poa Annua

The Poa Annua cultivar has survived the longest because it has evolved to thrive in many soils and temperatures. However, generally speaking, it favors moist, shaded areas. Discovering the finest pre-emergent for St. Augustine grass is the way to go since this short grass can withstand being cut to less than 1″.

Can preventive herbicides kill St. Augustine?

Pre-emergent weed killer should only be used on existing lawns since it will almost surely damage newly reseeded St. Augustine or freshly laid sod. This is because most selective herbicides are intended to prevent seeds from sprouting, and new root systems may not be strong enough to withstand them, possibly causing lethal harm.

A weed killer carefully prepared to target the different biology of weeds without substantially impacting established lawns is the appropriate preventive weed killer for St. Augustine grass.

Review Of The Top Pre-Emergent Weed Killers For St. Augustine

After discussing the many weeds you may need to remove, it’s time to decide what would work best for your lawn and look at some preventive treatments I’ve tried over the years.

I used performance, cost-efficiency, customer happiness, and the ingredients and efficacy of the items as my selection criterion. Continue reading to learn all you need to know about selecting the product that best meets your requirements.

1. The Andersons Barricade Pre-Emergent Weed Control


  • Effective against henbit, goosegrass, crabgrass, and poa annua
  • Weed killer that is good for lawns and garden borders
  • When applied around border plants, it has little influence


  • Water must be used to activate it.

Removing weeds from your valued St. Augustine lawn and the borders of your gardens without injuring the majority of ornamentals is an excellent benefit of Anderson’s Barricade. And after reading the “protected plant list” on the bag, I decided to try this.

This one does need watering since it only kills weeds that come into touch with the granules and water. But it’s okay since I would be watering anyway.

I applied Anderson’s granules to my beds after the last spring frost while wearing protective gear to avoid skin sensitivity. This specific herbicide was created to target the biology of weeds, and it is powered by prodiamine. I was pleased to see unattractive weeds fading off after a week, leaving my perennials untouched. For more on Anderson’s Barricade Pre-Emergent Weed Control, click.

The only downside was that I should have brushed the grains into my borders before watering, leaving stains behind. It’s also crucial to remember that when these granules are watered in and given time to dry, your grass will be secure for use by both humans and animals.

2. The pre-emergent herbicide Quali-Pro Prodiamine


  • 5lb bottle suitable for numerous applications or up to 44,000 sq feet
  • Great value for the money
  • Prevents a variety of weeds’ seeds from germinating


  • For use only on newly planted weeds.

This alternative has to be watered in and may be used on lawns and decorative beds. I appreciated the extensive list of weeds it controls and that one 5-pound container can treat up to 44,000 square feet when sprayed with a sprayer. If you have a smaller area to treat, you may use numerous treatments for the exact cost. View the pricing for Quali-Pro Pre Emergent here.

Remember that this one was designed to stop seed germination. On sprouting seedlings, it has little impact. I experimented with it in the spring and autumn on a small lawn and perennial borders. It took some time before I could fully capture the effect of this product since it continues to function for up to 6 months. But with time, I did see a lot fewer weed seedlings.

Lawns and gardens are safe for everyone after being soaked in the solution and allowed to dry, despite the fact that first skin contact may produce irritation or a rash.

3. Pre-emergent Crab-Grass Control For Lawn Bonide DuraTurf


  • Blocks a variety of weeds’ root development.
  • We need just a straightforward application for the whole season.
  • Does not leave paving stones or sidewalks stained


  • For more significant tasks, more than one bag can be necessary.

This Bonide weed killer also handles many weeds in garden beds and lawns. Using the active component Dithiopyr prevents weed growth at the root level in both seedlings and existing weeds. Although it covers less surface area than comparable products, the straightforward application process was unquestionably a bonus.

While wearing safety gear, I put this on my front lawn and flower beds at the suggested period (early spring). The Dithiopyr stops future root development by preventing cell division and expansion after weed seeds germinate and produce roots. Up to four months might pass between applications. From Amazon.com, get Bonide Crabgrass Pre-Emergent by clicking here.

In addition, it doesn’t discolor border stones or pavement. The only drawback is that more than one bag can be required, depending on how bad your weed infestation is. Additionally, waiting a day or two before spending time in the targeted regions is advised owing to the dust created during the treatment.

4. Southern Ag’s St. Augustine Grass Weed Killer with Atrazine


  • Includes a long list of weeds
  • Removes firmly entrenched weeds
  • Stops seeds from germination


  • For more extensive regions, more than one bottle could be required.

This potent pre-emergent herbicide is designed especially for St. Augustine grass. Using this product in garden borders is not advised since it is not selective. The second-widest variety of weeds on my list includes Poa annua, chickweed, woodsorrel, and knotweed.

Atrazine, the active component, operates differently. It is taken by weed roots that are already well-established, spreads via stems and leaves, and then prevents photosynthesis (which is required for growth and seed production). Additionally, it prevents seed germination.

On my backyard grass, where I experimented with it, all those unsightly, light green areas started to fade after two weeks. My St. Augustine grass filled those spaces up at the end of the season, giving it a more even look. Here are the costs for Southern Ag’s Atrazine St. Augustine Grass Weed Killer.

The only drawback is that a pump sprayer is required for application. If you want to apply it to broad areas, you may need a bigger sprayer and more than one bottle. But considering its effectiveness, it’s worthwhile!

5. High-Yield Fertilome Turf and Ornamental Grass Stopper


  • Easy to use
  • Stops roots from spreading and developing
  • Prevents the germination of seeds


  • To be used effectively, it must be done so at precise times.

Next up is a selection from Fertilome. Since it wasn’t explicitly designed for St. Augustine grass, I wanted to evaluate its efficacy using a small quantity per square foot. I used it in my perennial beds and a small area of weed-infested grass. Any implanted weed seeds will become free and rise to the soil’s surface if initially tilled. Once again, read the “protected plants” list on the packaging.

To make this work, water must be added. Additionally, the giant bag is more cost-effective since this should be used in the spring and autumn. Click here to see Fertilome Weed & Grass Stopper.

Dithiopyr, the active component, stops roots from developing when they emerge from the seed. Wearing protective clothes when applying with your spreader is also advisable. I did see some browning areas on the grass after a few days, but generally, not too horrible. My perennial flowerbeds were spotless as new!

6. Granules from Spectracide Weed Stop Plus Crabgrass Preventer


  • Includes more than 200 different species of weed
  • Quick results
  • Spraying in the spring and autumn prevents weeds from growing on lawns.


  • Water supplies and untargeted plants might be negatively impacted.

The last item I chose is from Spectracide. The broadest selection of weed species on my list, this potent herbicide and crabgrass preventer for St. Augustine grass uses three active chemicals to destroy over 200 distinct weed varieties. This should only be used on grass due to its aggressive weed-eliminating approach. Or next to any body of water.

I tried this on a large area of grass that was somewhat overrun with various weeds while using a lot of protective gear (and cleaning my hands afterward). When the temperature was about 13C in the spring and the autumn, I used a backpack sprayer to apply an even application. For Spectracide Weed Stop Granules, click here.

I tried it dry, and it went a bit heavier since there were so many weeds, even though the label recommends applying it on wet grass. The combination of active substances worked well and promptly provided effects. I saw weeds beginning to brown and wither by day’s end.

Pre-Emergency Use in St. Augustine

The active component in the pre-emergent product you chose and how it functions will determine the optimal timing to administer it. However, the best application seasons are often in the early spring and autumn. To succeed, one must always be one step ahead of the competition, which is the case when weeds are actively generating seeds or when those seeds are just beginning to germinate.

How to Submit a Pre-Emergent Request in St. Augustine

When the outdoor temperature is approximately 13C/55F, pre-emergents work best. Any lower and active components risk becoming inactive. If you raise the mixture over that, your grass might be burned.

Your choice of product will determine the appropriate application method. A push spreader may be more effective when applying a granular one over a big grass area. Applying water-soluble ones using a backpack or handheld sprayer is simpler.

Can weeds be eliminated without putting St. Augustine at risk?

Make sure the herbicide you choose is the best pre-emergent for St. Augustine grass by carefully reading the label. This will guarantee the health of your lawn. For this grass kind, all of the choices I tried performed well. So feel free to click the links for a secure purchase to save time.


Best Weed Killer

The result is in after many thorough experiments! All six of my suggestions have successfully weeded St. Augustine grass to varied degrees. Many active substances and application techniques are utilized to address this from various directions. This lets you choose a solution that meets your demands and end objectives.

You now have a choice, therefore. Will it be Anderson’s Pre-Emergent Weed Control, a granular mixture that may be applied in borders to prevent weeds from encroaching on your precious lawn?

Or you would like the simplicity of a Quali-Pro water-soluble choice. Although it is applied using a sprayer, it provides weed protection for your grass and your borders.

Alternatively, are you seeking Bonide | DuraTurf Crab-Grass Pre-Emergent Control for Lawn? This may be used on northern and southern lawns, such as St. Augustine, and is wildly successful in eliminating crabgrass over the long run.

Maintaining a healthy and beautiful St. Augustine grass lawn is achievable with a well-timed application of the best pre-emergent weed killers. These weed killers are efficient in preventing the growth of both broadleaf and grassy weeds, ensuring you have a weed-free lawn to enjoy. Remember, the best weed killers not only control weeds before they emerge but also kill weeds that have already sprouted.

Post-emergent weed control becomes necessary when weeds have already established in your lawn. Though they require a different approach, choosing the best post-emergent weed killer is equally important to maintain the aesthetic appeal of your St. Augustine grass lawn. Therefore, a combination of pre-emergent and post-emergent strategies can provide comprehensive weed control.

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