One of the most annoying parts of lawn maintenance is keeping it from being invaded by weeds. Weeds need water, sunlight and contact with the soil in order to survive. Given that these three requirements are the same things St. Augustine grass needs, weeds become an unavoidable part of lawn care.
St. Augustine has a very thick lateral growth habit—in fact, certain varieties like Palmetto® and CitraBlue® St. Augustine form an even thicker canopy than other St. Augustines. A dense carpet of grass is welcomed, not only because it looks good, but because it chokes out weeds and competes for space against them.
Even still—weeds may show up any time of the year in St. Augustine home lawns. Some of the most common ones in St. Augustine include chickweed, Poa annua and crabgrass. It’s always a good idea to know which types of weeds are growing in your grass. It can tell you a lot about your soil since certain weeds prefer specific soil conditions, and it allows you to come up with a treatment strategy designed for the types of weed you may be experiencing.
Read on to learn about common St. Augustine grass weeds, non-chemical control methods, preventative solutions and treatment strategies.
Common Weed in St. Augustine Grass Lawns
In addition to chickweed, Poa annua and crabgrass, there are actually an abundance of weeds that like to grow in St. Augustine. First, it is good to know that there is a difference between broadleaf and grassy weeds. Oftentimes, you’ll find broad-spectrum herbicides labeled to treat broadleaf weeds as opposed to grassy weeds. Broadleaf weeds, as the name suggests are weeds with thicker leaves like dollar weed. Grassy weeds are more difficult to spot because they resemble grass blades and blend in with your lawn.
The most common broadleaf weeds in St. Augustine grass are chickweed, henbit, clover and dollar weed.
Pictured above from left to right: chickweed, henbit, clover and dollar weed.
Some of the grassy weeds that are frequently spotted in St. Augustine grass are Poa annua, crabgrass, dallisgrass and bermudagrass.
Pictured above from left to right: poa annua, crabgrass, dallisgrass and bermudagrass.
If you are able to identify the weed you are seeing at home, you can make a more informed choice of which products to use by reading their labels. Be sure to read the product labels thoroughly so that you know if the chemical can be applied to your lawn without damaging the grass. Follow the product label’s instructions upon application. For more information, read Identifying Common Lawn Weeds. It is important to know that there are a few cultural, non-chemical control methods for weed control you can use as well.
Cultural Methods of Weed Control in St. Augustine Grass Lawns
Having a healthy lawn is the first and most important step to weed control. Performing regular maintenance practices like mowing, fertilizing and irrigation helps promote healthy growth. Mowing at the right times and at an appropriate height of 2–4 inches is ideal.
Mowing reduces the opportunity for weeds to sprout seed heads and spread. It also gives you the chance to walk every part of your lawn regularly so you can keep an eye out on other potential weeds. Be sure to bag up the grass clippings. Although spreading bag clippings on your lawn can serve as vital nutrition for your lawn, it also places any seed heads you just mowed right back into your grass. Sometimes mowing your own lawn in place of paying someone else to do it helps because they won’t be bringing over leftover grass clippings on the blades of the mower. These leftover grass clippings and seed heads can find their way into your lawn and create weeds. This is especially prevalent with leftover bermuda grass seed heads on mower blades.
Secondly, a regular fertilizer schedule will really contribute to your lawn’s thickness. Although fertilizer may seem counterproductive for weed control because its nutrients that promote growth, it helps your grass form a dense, thick layer above the surface of the soil and in the root zone so that weeds have to compete for space. Apply fertilizer regularly to help your St. Augustine grass stay lush and healthy. Sod University recommends the Lawnifi® Fertilizer Program. For those who prefer traditional granular fertilizers, Lawnifi also offers Foundation, a granular fertilizer that can be used anytime during the active growing season. Read Why Use Lawnifi Fertilizer? for more information.
Lastly, if there is a small amount of weeds present in your St. Augustine lawn, simply hand pull them. This can be ineffective when a large amount of weeds are present though. For more information, read our Weed Control in Your Lawn & Garden blog and check out our St. Augustine Homeowner Maintenance Guide.
Pre-Emergent Weed Control in St. Augustine Grass Lawns
Pre-emergent and post-emergent herbicides differ from each other. A pre-emergent herbicide, as it’s name implies, prevents weeds before they emerge from the soil’s surface. A post-emergent treats any current weeds you may see. If you know your St. Augustine is plagued by crabgrass in the spring and summer season, applying a pre-emergent in the spring as temperatures start to warm up prevents it from sprouting. This can reduce time, money and backache spent on removing the weeds.
Check out some of our top recommendations for pre-emergent herbicides for St. Augustine grass below.
- Coverage: 50 lbs. covers about 12,500 sq. ft.
- Active Ingredient(s): Prodiamine 0.37%.
- Ease of Use: Requires granular drop or broadcast spreader for application.
- Best Used On/For: Established warm and cool season turfgrass before weeds appear.
Prodiamine 65 WDG$109.95
- Coverage: 5 lbs. covers between 50,000–80,000 sq. ft.
- Active Ingredient(s): Prodiamine 65%.
- Ease of Use: Requires tank mixing and application with a sprayer.
- Best Used On/For: Established turfgrass before weeds appear.
Dimension 2 EW – 1/2 Gallon$149.95
- Coverage: 0.5 gallon covers between 87,000–228,000 sq. ft.
- Active Ingredient(s): Dithiopyr 24%.
- Ease of Use: Requires tank mixing and application with a sprayer.
- Best Used On/For: Established turfgrass before broadleaf weeds appear.
Post-Emergent Weed Control in St. Augustine Grass Lawns
Post-emergent weed control for currently existing weeds in St. Augustine grass is completely different than that of most other grasses. St. Augustine, as well as centipede grass, are sensitive to certain chemicals found in popular herbicides such as 2,4-D, dicamba, MCPP and MSMA. These active ingredients will actually damage your St. Augustine grass lawn.
When looking for a post-emergent herbicide that treats current weeds after they’ve “emerged” from the soil’s surface, you should select an herbicide with the active ingredient, Atrazine. When applied properly, Atrazine will control weeds without damaging your St. Augustine grass lawn. Take a look at some of our Atrazine products below.
Hi-Yield Atrazine Weed Killer$16.95 – $19.95
When using control products, be sure to read the product labels thoroughly so that you know if the chemical can be applied to your lawn without damaging the grass. Follow the product label’s instructions upon application. Lastly, if you enjoyed reading this information, a few other recommended Sod University articles for St. Augustine is How to Use Spectracide Weed Stop for Lawns for St. Augustine and Centipede and All About St. Augustine Sod.