5 Best Weed Killers for St Augustine Grass

Planted in the right areas, St. Augustine grass is an unsurpassed choice for lawns in several southern states including Texas, Florida, California, and Hawaii. 

As much as I like St. Augustine’s grass and have planted it twice, mainly as an alternative to a Bermudagrass lawn, it is one of the few grass types that can crowd out weeds, but not all of them including chickweed, poa annua, and crabgrass. 

If weeds have plagued your St. Augustine partial or entire lawn, there’s no need to break a sweat just yet because here are the best weed killers for weed control in a St. Augustine grass lawn including pre-emergent products, post-emergent herbicides, and natural treatments for weeds. 

Best Weed Killers for St Augustine Grass
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5 Best Weed Killers for St. Augustine Grass

1. Natural Armor Weed and Grass Killer All-Natural Concentrated Formula – Best Organic Weed Killer for St. Augustine Grass

Natural Armor Weed and Grass Killer All

The Natural Armor weed killer is a glyphosate-free formula that kills over 250 weeds and grasses when used under the right conditions. 

  • Liquid vs. Granular – Liquid 
  • Pre-emergent vs. Post-emergent – Post-emergent to control weeds
  • Selective vs. Non-Selective – Non-selective 
  • Organic and Natural? – Natural 
  • Kills Weeds Within? – Hours 
  • Safe for St. Augustine – Yes 

If you prefer using natural methods to eliminate weeds growing above and below the soil in St. Augustine grass turfs, the Natural Armor weed killer is a great option. Unlike other similar products that take weeks or more to showcase results, the Natural Armor weed killer works quickly within just 24 hours after application. 

Adding to this, it doesn’t contain any harmful chemicals, making it safe to use for people, pets, and the environment. With the Natural Armor organic weed killer, there’s no messy mixing or diluting required but simply use the included trigger spray or fill up a pump sprayer and apply the solution to the targeted area on a calm sunny day. 

Pros:

  • Can be used in several areas including flower beds, edging, and fencing lines 
  • Visible results in just 24 hours 
  • Safe for use around humans and pets 
  • Kills 250+ types of weeds and grass 
  • Doesn’t contain any harmful chemicals 

Cons:

  • Non-selective – will kill all plants it comes in contact with 

Personal Verdict:

If you’d like to steer clear of a chemical pre emergent herbicide, and a broad-spectrum herbicide, the Natural Armor weed killer is hard to beat, especially against broadleaf and grassy weeds. I used it briefly to spot-treat crabgrass weed and around grass blades in my St. Augustine lawn and the results were quite impressive. 

Natural Armor Weed and Grass Killer All-Natural Concentrated...
5,444 Reviews
Natural Armor Weed and Grass Killer All-Natural Concentrated...
  • CONTAINS NO GLYPHOSATE - Natural, Concentrated Formula For Making 250+ Types of Weeds and Grasses Stop Right in Their Tracks. Weeds and Grass Will Look Like You Took A Torch To Them.
  • EASY TO USE - People & Pet Friendly. Ready To Use, Just Spray and Go. No Messy Mixing or Diluting.
  • PLACES TO USE - Use Anywhere You Don't Want Weeds and Grass Growing Such As, Around Flower Beds, Shrubs and Trees, Barns, Driveways, Edging, Fence Lines, Foundations, Gravel Areas, Mulch Beds, Overgrown Weed Areas, Parking Areas, Patios, Pavers, Pool Areas, Rock Walls and Pathways, Walkways, Wells & Water Systems. Any Location Where No Vegetation is Wanted

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2. Spectracide Weed & Grass Killer – Best Chemical Herbicide for St. Augustine Grass 

Spectracide Weed & Grass Killer

Spectracide is one of the best weed killers for a variety of grass weeds growing in St. Augustine lawns for several good reasons, starting with its ability to kill weeds and grasses down to the roots.

  • Liquid vs. Granular – Liquid to effectively eliminate weeds
  • Pre-emergent vs. Post-emergent – Post-emergent
  • Selective vs. Non-Selective – Non-selective
  • Organic and Natural or Chemical? – Chemical 
  • Kills Weeds Within? – 3 Hours
  • Safe for St. Augustine – Yes

Spectracide is one of my go-to weed killers for St. Augustine and many other types of turfgrass including warm-season grass like centipede grass and annual grass. This non-selective herbicide kills pesky weeds and grasses and is rainproof in just 15 minutes after the initial application. 

This powerful formula is ready to use right out of the bottle with no mixing required with water and delivers great results within three hours. Best of all, Spectracide kills weeds down to the roots, a feature that’s missing in most homemade weed-killer solutions including vinegar and dish soaps or boiling water. 

Pros:

  • Kills weeds down to the roots 
  • No mixing is required 
  • Kills weeds in grass lawn within 3 hours after application
  • Can be used around driveways, walkways, and fences  

Cons:

  • Application equipment not included

Personal Verdict:

Spctracide kills weeds down to the roots so all you have to apply the product and clean up the mess in a few days. What’s even better is it is rainproof in just 15 minutes after application.

Spectracide Weed & Grass Killer + AccuShot Sprayer
  • Kills weeds, grasses and the roots; visible results in as little as 3 hours. Use on driveways, walkways and around fences, trees, flower beds, shrubs.
  • Includes continuous power AccuShot Sprayer with extendable wand for precise application.
  • Rainproof - rainfall or watering 15 minutes after application will not wash away effectiveness.

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3. Ortho WeedClear Weed Killer – Best Weed Killer that Won’t Kill St. Augustine Grass 

Ortho WeedClear Weed Killer

Ortho WeedClear, brought to you by The Scotts Company LLC, is a unique formulation that kills over 250 common broadleaf weeds in St. Augustine lawns but won’t harm your grass when used according to the manufacturer’s application instructions.

  • Liquid vs. Granular – Liquid
  • Pre-emergent vs. Post-emergent – Post-emergent
  • Selective vs. Non-Selective – Selective
  • Organic and Natural or Chemical? – Chemical
  • Kills Weeds Within? – Quick
  • Safe for St. Augustine – Yes

The list of weeds Ortho WeedClear can tackle includes dandelions, chickweed, clover, and poison ivy. Ortho WeedClear is rainproof within an hour after application, after which people and pets can enter the treated area. 

This selective herbicide shows results within hours and is easy to use with the included comfort wand or trigger spray. 

Pros:

  • Rainproof in an hour 
  • Works quickly to kill targeted weeds and control weed growth
  • One of the effective methods to kill weeds and not grass 
  • Can be used in acidic soil and alkaline soils 
  • Comes with a comfort wand 

Cons:

  • The quality of the comfort wand needs improvement 

Personal Verdict: 

I’ve used Ortho WeedClear to wipe out lawns and for spot treatments in specific areas of my turf. In both instances, this selective herbicide proved to be an effective method of weed control and showed impressive results within a few hours instead of a couple of weeks or more with other herbicides. 

Ortho WeedClear Weed Killer for Lawns: Refill, Won't Harm Grass...
4 Reviews
Ortho WeedClear Weed Killer for Lawns: Refill, Won't Harm Grass...
  • The information below is per-pack only
  • Use Ortho WeedClear Weed Killer for Lawns refill to kill weeds down to the root, without harming your lawn (when used as directed); you'll see visible results in hours
  • KILLS WEEDS: This lawn weed killer kills over 250 common weeds, including dandelions, clover, poison ivy, chickweed, and dollarweed (see product label for complete weed list)

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4. Roundup Max Control 365 

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Whether you’re a novice or a seasoned gardener, you’ve probably heard about Roundup at some point – the killer (literally) non-selective herbicide that can be used on driveways, sidewalks, and gravel areas. 

  • Liquid vs. Granular – Liquid
  • Pre-emergent vs. Post-emergent – Post-emergent
  • Selective vs. Non-Selective – Non-selective
  • Organic and Natural or Chemical? – Chemical
  • Kills Weeds Within? – 12 hours 
  • Safe for St. Augustine – Yes

Roundup Max Control 365 is the latest launch from the company and delivers much better results than its previous iterations. It not only kills and prevents weeds for up to 12 months but kills most types of weeds right down to their roots. 

Max Control 365 can be used in several different areas of your property and is rainproof in 30 minutes. Weeds usually die completely within a couple of days after treatment, making it easy to start the recovery process to achieve a lush, green lawn. 

Pros:

  • Kills most common types of weeds 
  • Prevents growth of weeds up to 12 months
  • Can be used almost everywhere on your property
  • Rainproof in 30 minutes 
  • Kills weeds down to the roots for a healthy lawn 

Cons:

  • Another round of application is needed for tough weeds 

Personal Verdict: 

Roundup works exactly as agreed, killing weeds and preventing them from cropping up for up to a year. The included wand is a nice touch so you can get started as soon as you receive the product. 

Ortho Weed B Gon Weed Killer for Lawns Ready-To-Use2 with Comfort...
1,972 Reviews
Ortho Weed B Gon Weed Killer for Lawns Ready-To-Use2 with Comfort...
  • Lawn-friendly weed control
  • Won’t harm the lawn (when used as directed)
  • Kills weeds to the root

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5. Southern Ag Amine 2

Southern Ag Amine 2

Slotting in at the #5 position on this list of best weed killers for St. Augustine lawns is none other than the Southern Ag Amine 2 herbicide. Southern Ag’s weed killer is formulated to control several broadleaf weeds and woody plants and can be used safely on southern grasses like St. Augustine. 

  • Liquid vs. Granular – Liquid
  • Pre-emergent vs. Post-emergent – Post-emergent weed control
  • Selective vs. Non-Selective – Non-selective
  • Organic and Natural or Chemical? – Chemical
  • Kills Weeds Within? – A few days to a week following treatment
  • Safe for St. Augustine – Yes

Southern Ag Amine 2 is no newcomer to the chemical herbicide space but has been used extensively for residential as well as commercial applications around the country. 

It features an economical use rate of just 1 to 4 pints per acre and comes in a in a low volatile amine form. This is a concentrated formula that must be mixed at the rate of 3 – 5 gallons of water to cover 1,000 sq. ft.

Pros:

  • Controls many broadleaf weeds and woody plants 
  • Economical application at 1 to 4 pints per acre
  • Low volatile amine form.
  • Can be used for residential and commercial applications
  • Kills weeds within a few days to a week following treatment

Cons:

  • Can’t be used in original condition/should be diluted with wat
Southern Ag Amine 2,4-D WEED KILLER, 32oz - Quart
6,578 Reviews
Southern Ag Amine 2,4-D WEED KILLER, 32oz - Quart
  • Low, economical use rate of 1 to 4 pints per acre
  • Controls many broadleaf weeds & woody plants
  • Use in turf, pastures, rangeland, ditch banks, fences…

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Best Weed Killer for St. Augustine Grass Buying Guide 

Buying the best weed killer for St. Augustine grass requires careful consideration because applying the wrong product can be detrimental to your lawn’s health. Regardless of the weed killer you choose, it’s important to follow the instructions on the product label for proper application. 

How I Chose the Best Weed Killer for St. Augustine Grass? 

Choosing the best weed killer for St. Augustine lawns was pretty easy for me because I’ve dealt with the exact same issue on several occasions and hence used myriad different weed killers. 

I chose the 5 weed killers on this list based on two factors – effectiveness and number of weeds the product can kill. 

Should I Use a Pre-Emergent Weed Killer or a Post-Emergent Weed Killer for St. Augustine Grass?

Just like the name suggests, pre-emergent herbicides prevent weeds from germinating in the first place and post-emergents kill weeds that are already on your lawn. 

I ideally apply a pre-emergent in the early spring before the weeds grow and late spring or early summer for grassy weeds. Rule of thumb- to effectively kill weeds, apply a pre-emergent or post-emergent 30 minutes to an hour before it rains or else the herbicide may be washed away. 

Should I Choose Liquid or Granular Weed Killer for St. Augustine Grass? 

Liquid weed killers are generally a great option as they work quickly and provide consistent results compared to granular form. 


Final Thoughts

When shopping for the best weed killer for St. Augustine grass, there are plenty of options to choose from. But the 5 products mentioned on this list work quickly and are effective at killing a variety of weeds that affect St. Augustine grass lawns including crabgrass. 

You may prefer to pick a fertilizer and weed killer combo. In this case, check out the best fertilizer for St. Augustine grass.

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