Best Weed Killer for St Augustine Grass

What is the Best Weed Killer for St. Augustine Grass?

A warm season grass that grows in tropical and subtropical climates, St. Augustine grass will give you a thick green lawn when given the right moisture and nutrients, plus it has great weed control. There are times though when it is necessary to apply a herbicide to control the unwanted weeds in your St. Augustine lawn, so it is important to know how to remove weeds from St Augustine grass so that you don’t also kill your lawn. Here are a few tips on what to look for in the best weed killer for St. Augustine grass and a few reviews to help you start shopping to get the best lawn care St. Augustine grass.

Post or Pre-Emergent Herbicides

You are probably familiar with the two main options for weed killers, either pre or post-emergent herbicides. Pre-emergent herbicides prevent weeds from growing while post-emergent herbicides will actively attack the weeds that are growing in your St. Augustine grass.

To best control the weeds before they even start to grow, the pre-emergent herbicide should be placed on your grass when the average temperature is 65 to 70° F during the day for 4 consecutive days which for most St. Augustine grass areas which is usually in February or March. For controlling other weeds and winter annuals, treatment in the fall is usually in September when the average nighttime lows are between 55 and 60° F for four consecutive days.

Of the two, the pre-emergent herbicide is the best weed killer for St. Augustine grass to prevent weed germination. How do you apply weed killer? Here is a quick video tutorial to show you how to properly apply weed killer: 

Read the Label

Always read the label before applying any type of herbicide. Some herbicides only target certain plants and weeds so you need to identify weeds in St. Augustine grass to make sure the product you are choosing is right for your situation. St. Augustine grass can also be sensitive to specific herbicides that contain 2,4-dichlorophenoxyacetic acid, or 2,4-D.

This type of herbicide is used a lot for controlling broadleaf weeds and as a regulator of plant growth. Make sure to read your product label to see if the product you are choosing is safe and lists it as a use for St. Augustine grass.

Other Choices

Unhealthy lawns tend to be where weeds flourish the best, so having a healthy lawn is the perfect way to start to have a weed-free yard. When your St. Augustine grass has become damaged from pests or cultural problems, weeds start to take over so it is important to incorporate proper lawn management practices to keep weeds away that include mowing, watering, and proper fertilization.

It is recommended to mow your frequently at a low height between 2 1/2 to 3 inches, water only when it needs it, and fertilize it every eight weeks with a pound of water-soluble nitrogen for every 1,000 square feet. Interested in learning more about St. Augustine Lawn Care? Here is a video with professional lawn care tips: 

What is Atrazine for St Augustine?

Part of the triazine class, atrazine is an herbicide that is used to stop broadleaf weeds from growing in corn crops and turfs like residential lawns and golf courses. So, how long does it take for atrazine to work? When using atrazine, you should expect about 3 to 4 weeks to kill off the weeds in your yard.

If you are using this herbicide, how to apply atrazine to St. Augustine grass can be very specific with two applications throughout the year in November and January to control both broadleaf weeds as well as annual grasses. Interested in learning more about atrazine? Here is a helpful video that will give you the scoop on this popular weed killer: 

Types of Weeds

Broadleaf Weeds

In the spring after your lawn greens up, it is important to treat your St. Augustine grass with a herbicide that specifically treats broadleaf weeds like dandelions. Do not use herbicides that use 2,4-D, mecoprop, or dicamba to prevent damage but look for products that contain atrazine for St. Augustine grass.

Cool-Season Grasses

Look for a pre-emergent herbicide that contains dithiopyr control to treat cool-season grasses like crabgrass, bluegrass, and fescue as well as small-seeded broadleaf weeds. This type of herbicide can interrupt the growth process when applied correctly but do not use a pre-emergent herbicide on lawns that are over-seeded with annual ryegrass.

Perennials

Trying to manage hard to control broadleaf weeds and perennial grasses with a post-emergent herbicide that can kill any plant it touches can also damage your St. Augustine lawn if you aren’t careful. Instead of a broad application, you will want to use a thin stream of spray or apply the herbicide with a brush to certain grasses and weeds to lessen the potential damage to the surrounding St. Augustine grass.

Best Weed Killer for St. Augustine Grass Reviews 2018

When you are looking to kill and prevent tough weeds in your St. Augustine grass, the Image Herbicide for St. Augustine Grass is an easy-to-use concentrate that will starve your weeds to death. This is a selective herbicide designed to take on grassy weed control by targeting tough, broadleaf weeds. Using 4% atrazine, Image Herbicide Concentrate is effective for controlling weeds in Centipedegrass and St. Augustine grass.

With a concentrated formula, Image Herbicide has an easy and fast application that kills bothersome weeds on contact and will cover over 3,000 square feet. It is effective at controlling spurweed, sandspur, and dollarweed as well as bluegrass and Florida betony. 

PROS

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    Hard to find a good product like this for St. Augustine grass
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    Weeds start dying after a few weeks but grass is fine
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    According to Image herbicide reviews, this product can really take care of out of control weeds, great value for a good product

CONS

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    Can be spotty for some users only working in patches
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    Fine line with too little or too much, have to be very careful with amounts

One of the best weed killers available for St. Augustine Grass, Ortho Weed-B-Gone Weed Killer will easily kill more than 200 weeds without damaging your yard. Outfitted with a ready-to-use spray bottle, this is an easy-to-use product that gives you application control over large areas. With Ortho Weed B Gon Weed Killer, you get a guaranteed product that will kill your weeds down to their roots.

This easy-to-use product is rainproof in about an hour and will not wash away. Ortho Weed-B-Gone includes a nozzle that is easy to attach your hose to that includes a washer to lock the nozzle in place. It also features a three-way switch that allows you to run water through the nozzle to rinse it out. 

PROS

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    Easy to connect the bottle to a hose
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    Great for use on broad areas of lawn
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    Dependable product that water won’t wash away

CONS

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    Takes a few weeks and a couple of rains to get the weeds to die
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    Doesn’t come with directions


Merging both pre and post-emergent herbicide, Bayer Advanced Weed & Feed both prevent weeds from germinating for up to six months. Bayer Advanced also strengthen your lawn with an incredible fertilizer and is perfect for use on St. Augustine grass, Bermuda Grass, Zoysia Grass, and Centipede Grass.

With just a single application of Bayer Advanced Weed and Feed, you will prevent new weeds from growing and kill existing weeds in your lawn including crabgrass for as long as six months. This weed and feed will also strengthen, feed, and green your lawn giving you thick and healthy green grass with weed control all season-long. This is a simple and easy product to use that won’t harm your lawn when you use it as directed, plus there is no need for consistent reapplications.

This innovative weed and feed is effective in killing existing weeds like clover, dandelion, and dollar weed. Plus, one bag can treat up to 5,000 square feet of lawn. This is a simple and effective solution for any homeowner that wants to create a green lawn that is weed free all year long. 

PROS

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    Grass is kept in great condition and gets thicker
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    Grass is kept in great condition and gets thicker
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    Gives you the best results when compared to its competitors

CONS

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    Can damage your lawn if you aren’t careful
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    Great as a fertilizer, not so great on weeds

When your grass and weed are actively growing, using Scotts Turf Builder Bonus S Southern Weed & Feed will help to get rid of existing weeds while creating a thicker law that will crowd out the growth of future weeds. Consistently feeding your lawn with Scotts Turf Builder will give it the nutrients it needs to look its best while also helps it to withstand the stress of weeds. This is also a great product to use during harsh weather conditions like drought and heat and works well on clover and dollar-weeds.

Scotts Turf Builder is a safe product to use on St. Augustine grass, Centipedegrass, Zoysia grass, and Carpet grass. This is a specifically designed formula for southern lawns that can cover up to 5,000 square feet and is sold in certain Southern States. 

PROS

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    Effective on dollar weeds
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    Great fertilizer, helps to build back your yard
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    Works great on lawns that are a mix of grass types

CONS

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    Can’t use it under shrubs or trees
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    Slow to work

Ideal for use with Centipede Grass and St. Augustine Grass, Southern Ag Atrazine Weed Killer takes on several types of broadleaf weeds and will also suppress crabgrass. This is both a pre-emergent and post-emergent product that is able to control already emerged weeds and take down weeds before they grow.

With the ability to control many common grass weeds, Southern Ag Atrazine contains 4% atrazine and can over 1,000 square feet. This is an effective form of weed killer for St. Augustine Grass that is good for both broad applications and spot treatments. 

PROS

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    More effective than other weed killers and doesn’t kill your grass
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    Also good for spot treatments
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    One application takes care of most of the weeds

CONS

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    Tedious application system
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    A hose end sprayer would work better for applying the product

Conclusion

The winner of the Best Weed Killer for St. Augustine Grass roundup is Image Herbicide. Using Atrazine, Image Herbicide is tough on your weeds preventing and killing controlling weeds that grow in Centipedegrass and St. Augustine grass. This selective herbicide was created to take on tough, broadleaf weeds with an easy-to-use concentrate that is designed to starve weeds to death.

Image Herbicide uses a fast and easy application that kills weeds on contact covering over 3,000 square feet. It targets spurweed, sandspur, and dollarweed as well as bluegrass and Florida betony. The definite winner of the Best Weed Killer for St Augustine Grass roundup is Image Herbicide for St. Augustine & Centipede grass hands down.

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