How to Kill Weeds in St. Augustine Grass

Weeds can be a huge problem for St. Augustine grass lawns. No one wants to look at them, and they can spoil the look of a well-maintained lawn. But, it is difficult to eliminate these weeds from your lawn. They can compete with the grass for water, sunlight, and nutrients, leading to thinning or dying grass. In this guide, we will discuss how to kill weeds in St. Augustine grass lawns using both chemical and non-chemical methods.

What types of weeds can you find in St. Augustine grass?

There are two types of weeds that commonly grow in St. Augustine grass lawns: broadleaf and grassy.

Broadleaf weeds have a wider leaf (compared to the blade of grass) while the latter resembles the blades of St. Augustine grass’ leaves, but they can be distinguished by their darker color or faster growth rate than your turfgrass species.

Broadleaf weeds on St. Augustine grass lawn: How to recognize and control them?

  1. Dollarweed – it has round, silver dollar-like leaves with serrated edges & yellow flowers on stalks; control methods include applying pre-emergent & post-emergent herbicides such as dithiopyr (Dimension), flumioxazin (Broadstar), or prodiamine (Barricade)
  2. Henbit – has square, purplish leaves; can be controlled by applying post-emergent herbicides such as glyphosate
  3. Spurge – has narrow, green leaves with red veins and a milky sap when broken; control methods include using glyphosate or an ortho ester formulation of triclopyr.
  4. Clover – has round to oval-shaped, white flowers & three leaflets per leaf; can be controlled using pre-emergent herbicides such as pendimethalin (Pendulum) or isoxaben applied in late winter to early spring
  5. Purslane – has a reddish stem and paddle-shaped leaves; can be controlled using pre-emergent herbicides such as pendimethalin (Pendulum) applied in late winter to early spring or post-emergent herbicides such as glyphosate (Roundup).

 

Grassy Weeds

  1. Crabgrass – it is an annual grass that can grow up to 20 inches tall, its stems are light green and the seed heads are reddish-brown; control methods include using pre-emergent herbicides such as prodiamine (Barricade) or atrazine (AAtrex) applied in late winter to early spring.
  2. Bermudagrass – it is a perennial grass that can grow up to 24 inches tall, its stems are light green and the seed heads are purplish-brown; control methods include using post-emergent herbicides such as glyphosate (Roundup), glufosinate, or imazapyr + sulfometuron methyl.

 

How to kill weeds in St. Augustine Grass

 

Non-chemical methods:

There are a number of non-chemical methods that can be used to kill weeds in St. Augustine grass lawns. One of the most effective methods is hand pulling or hoeing the weeds out of the lawn.

Another method is mulching, which involves covering the bare soil with a thick layer of mulch to prevent sunlight from reaching weed seeds. This will eventually kill the weed plants.

Finally, you can also use a flame weeder to kill weeds in St. Augustine grass lawns. A flame weeder is a tool that uses heat to destroy weed plants. It is important to note that not all weeds are killed by using these methods; some of the tougher weeds may require the use of herbicides for complete control.

Chemical Method:

There are a number of herbicides that can be used to kill weeds on St. Augustine grass lawns. The most popular and effective herbicide for this purpose is glyphosate.

Other herbicides that can be used include dicamba, atrazine, and simazine. When using any of these herbicides, always read and follow the label instructions carefully.

Applying herbicides to kill weeds

There are many herbicides available to homeowners for controlling weeds in St. Augustine grass lawns. The most important factor to consider when using herbicides is the time of year that you are applying them.

Pre-emergent or post-emergent herbicides should be applied depending on the type of weed you are trying to control.

Pre-emergent herbicides

Pre-emergent herbicides should be applied prior to weed germination, which usually occurs in late winter or early spring. These herbicides work by inhibiting the weed seed from sprouting and growing. Some common pre-emergent herbicides used for killing weeds in St. Augustine grass include pendimethalin, prodiamine, and isoxaben.

Postemergent herbicides

Post-emergent herbicides are applied after the weed has germinated and started to grow. These herbicides work by killing the weed plant. Some common post-emergent herbicides used for killing weeds in St. Augustine grass include glyphosate, glufosinate, imazapyr + sulfometuron methyl, and dicamba + mecoprop + diclorprop.

Step-by-step process of getting rid of weeds without harming St. Augustine grass

St. Augustine grass, also known as Stenotaphrum secundatum, is a common lawn grass in the southern United States and California. While it is not cold-hardy, it has a deep root system that allows it to survive in hot climates where other grasses might not. It also has a tendency to spread, which can make weeding St. Augustine lawns difficult.

If you have a lawn with this type of grass, you can use different methods to kill weeds without harming the grass itself.

Step 1

Spray weeds with ready-to-use weed killers containing glyphosate for broadleaf weeds or dicamba for creeping and broadleaf weeds. You can buy these chemicals individually or in combination at any garden supply store. Follow the directions on the label for spraying individual plants using either method. The glyphosate or dicamba will kill the weeds without harming your St. Augustine grass.

Step 2

Apply a pre-emergent herbicide in the spring if you live in an area with warm winters. Apply it in early autumn if you live in an area where winters are cool but not freezing, such as Georgia or Texas. Pre-emergents prevent seeds from germinating so they don’t have a chance to grow.

Step 3

Apply post-emergent herbicide in the summer if you live in an area with warm winters. Apply it at any time of the year if you live in an area where winters are cool but not freezing. Post-emergents kill weeds that have already germinated and started to grow.

Regular mowing is also important for controlling weeds in St. Augustine grass lawns. Mow your lawn at least once a week, making sure to remove all the clippings from the lawn when you are done. This will help prevent weed seeds from being able to germinate and grow.

Herbicide application tips

While herbicides are very effective tools for controlling weeds in St. Augustine grass, they can also be dangerous if not used properly. Here are some tips for applying herbicides safely:

  • Always follow all instructions on the product’s label;
  • Never apply more than the recommended amount of any pesticide or mix different pesticides together unless directed by a qualified expert such as an extension agent.
  • When mixing pesticide concentrates, add water slowly into the spray tank instead of adding water directly onto concentrated pesticides; this will help prevent splashing, which could cause skin or eye irritation.
  • When applying herbicides, always wear long pants, a long-sleeved shirt, shoes, and socks. Also, wear gloves, a hat, and safety glasses to protect your skin, eyes, and head.
  • Avoid spraying herbicides in windy conditions or near desirable plants as the herbicide may drift onto them and damage or kill them.

 

Frequently Asked Questions

 

How do you kill weeds and not grass?

Weeds can be killed with herbicides, but it is important to select the correct type of herbicide for your lawn. Pre-emergent weed killers should be applied before weeds germinate, and post-emergent weed killers should be used after they have already started growing; otherwise, you may end up killing both weeds and grass.

How do I get rid of weeds in my yard without chemicals?

To kill weeds without using chemicals, you will need to either pull them out by hand or smother them with organic materials such as cardboard or newspapers.

How do I keep grass from growing in gravel?

To prevent a gravel driveway from becoming overgrown with grasses and other plants that might cause problems in areas where cars need to drive, use a herbicide such as glyphosate or dicamba. These chemicals will kill any plants that come into contact with them without harming the gravel itself.

Can I use weed killer on my vegetable garden?

Weed killers can be used in gardens to control weeds, but it is important to read the label of the product you are using to make sure it is safe for vegetables. Some products are specific to certain types of plants and should not be used on others.

Will St. Augustine choke out weeds?

No, St. Augustine will not choke out weeds; in fact, it is possible for weeds to grow in the same areas as St. Augustine grass. However, using herbicides can help control weed growth and keep your lawn looking neat and tidy.

Conclusion

The best way to kill weeds in St. Augustine grass is to not let them get started in the first place. Since their roots travel underground and spread far, it can be tricky to completely eradicate an unwanted weed type. The best thing you can do is to remove any that you find on your property. You can also use weed-suppressive soil or landscape cloth as a barrier between your St. Augustine grass and invasive plant species.