Does your beautiful St. Augustine lawn look more like a weed parade lately? You’ve nurtured your grass, but those pesky invaders keep popping up, stealing the spotlight. It’s frustrating when you want that perfect, carpet-like lawn, but stubborn weeds fight back. Finding the right post-emergent herbicide is tricky because St. Augustine grass is sensitive. Use the wrong product, and you might end up with brown patches instead of green perfection.
Choosing the wrong weed killer can damage your prized turf, wasting your time and money. Many gardeners feel overwhelmed by chemical labels and confusing instructions. How do you zap the weeds without harming your St. Augustine grass? Don’t worry; we have the answers you need to win the war against lawn invaders.
This guide cuts through the confusion. We will show you exactly which post-emergent herbicides work safely and effectively on St. Augustine grass. By the end of this post, you will know how to confidently select and apply the right product for a lush, weed-free yard. Let’s dive into the best strategies for maintaining your vibrant St. Augustine lawn!
Top Post Emergent Herbicide For St Augustine Grass Recommendations
- NUTSEDGE KILLER FOR LAWNS — KILLS TUBERS BELOW THE SOIL. Most nutsedge sprays only scorch the leaf you can see, leaving the underground tuber to resprout in 7–10 days. Aethon Herbicide SL is powered by Vexis Technology — a dual-active blend of Penoxsulam 1.24% + Pyrimisulfan 1.24% that reaches the reproductive structures and breaks the regrowth cycle. Yellow nutsedge, purple nutsedge, annual sedge, and kyllinga rhizomes are destroyed at the root, not just burned at the surface.
- 26,000 SQ FT PER QUART — PROFESSIONAL POST-EMERGENT TURF HERBICIDE. Mix just 1.2–1.7 fl oz per 1,000 sq ft and treat up to 26,000 sq ft from a single 32 oz bottle — roughly a third of an acre. That works out to less per square foot than common single-active sedge killers. This concentrate replaces messy granular nutsedge products (WDG) with cleaner, more accurate liquid application — no clogged spreaders, no uneven coverage, no waste
- SELECTIVE WEED KILLER SAFE FOR YOUR LAWN — PET FRIENDLY ONCE DRY. A true selective post-emergent herbicide: it kills weeds, not your grass. Labeled for established Southern warm-season lawns including St. Augustine (Floratam and Bitterblue varieties), Bermudagrass, Zoysiagrass, and Centipedegrass. Children and pets can re-enter the treated area as soon as the spray has dried — no fencing off the yard for the weekend, no waiting days like with non-selective products.
- KILLS DOLLARWEED, DANDELION, DOVEWEED, VIRGINIA BUTTONWEED & 45+ MORE. University greenhouse trials confirm 100+ days of broadleaf control on the toughest Southern weeds — dollarweed (pennywort), dandelion, doveweed, Virginia buttonweed, white clover, ground ivy, wild violet, and plantain. One application of this concentrate replaces multiple rounds of generic weed-and-grass killers — fewer trips with the sprayer, longer-lasting lawn.
- LIQUID CONCENTRATE WITH NO MAXIMUM TEMPERATURE LIMIT. Engineered for Southern heat where ordinary herbicides scorch turf above 85°F. The Soluble Liquid (SL) formulation stays uniformly suspended in the spray tank — no settling, no clogged nozzles, consistent dosing from first gallon to last. Apply from late spring through fall and reseed in 2 weeks. From PBI-Gordon — the professional turfgrass brand trusted by golf courses, sod farms, and lawn care operators across the South.
- BROAD-SPECTRUM WEED CONTROL: Tenacity herbicide is a liquid lawn weed control solution labeled to control 46 broadleaf weed and grass species, including crabgrass, goosegrass, clover, dandelion, ground ivy, yellow foxtail, oxalis, yellow nutsedge and unwanted creeping bentgrass.
- APPLICATIONS AT SEEDING: Unlike most herbicides, Tenacity can be applied anytime you are seeding, including bare ground seeding or overseeding of established turf. View the label for the complete listing of tolerant turfgrass species.
- SELECTIVE PRE- AND POST-EMERGENT CONTROL: Based on a naturally occurring compound produced by the bottlebrush plant, Tenacity prevents new weeds from emerging while precisely targeting existing weeds, leaving your lawn and desired grass unharmed.
- EASY TO MEASURE AND POUR: No more lost syringes. Simply squeeze the bottle to place the precise amount of Tenacity needed in the dispensing chamber. Pour 1 tsp. per 2 gal. of water.
- TRUSTED ORIGINAL: Tenacity is the original leading herbicide brand containing the active ingredient mesotrione, which the manufacturer innovated more than 20 years ago. 94% of lawn care operators said Tenacity exceeded their expectations.
- Effective control of a variety of broadleaf weeds
- Combination of three powerful selective herbicides
- Flexible Application Rates – higher rates for problem areas, lower rates for turf maintenance
- Ideal for cool or warm season turf
- Labeled for sod farm usage
- Fast Acting Broadleaf Weed Control
- Professional Strength
- Kills most Broadleaf Weeds
- Easy to use
- 32-Count St Augustine ProVista SodPods: Includes 4 trays of 8 pods each (32 total). Each individual pod measures 3" x 3".
- Coverage Area: Once fully matured, each 32-count pack covers 72-sq ft when plugs are planted 18 inches apart (on center).
- Premium Texture: Broad, lush blades with uniform dense growth and vibrant green color
- Sunlight Needs: Performs well in full sun and moderate shade
- Seasonal Color: Rich green color that stays vibrant throughout the growing season
- 64-Count St Augustine ProVista SodPods: Includes 8 trays of 8 pods each (64 total). Each individual pod measures 3" x 3".
- Coverage Area: Once fully matured, each 64-count pack covers 144-sq ft when plugs are planted 18 inches apart (on center).
- Premium Texture: Broad, lush blades with uniform dense growth and vibrant green color
- Sunlight Needs: Performs well in full sun and moderate shade
- Seasonal Color: Rich green color that stays vibrant throughout the growing season
- Tenacity is a systemic pre-emergence and post-emergence herbicide for the selective contact and residual control of weeds in turfgrasses.
- When applied as a pre-emergent, weeds absorb Tenacity during emergence from the soil.
- Target pests: Barnyardgrass, Carpetweed, Chickweed, Clover, Crabgrass (large & smooth), Dandelion, Foxtail, Goosegrass, Henbit, Yellow Nutsedge, Purslane, Thistle, Wild Carrot and others
- Active Ingredient: Mesotrione 40%
- Date printed on bottle is Manufacture Date, not expiration. Shelf Life: 5-8 years from date of manufacture when properly stored. Keep out of direct sunlight and extreme temperatures
Choosing the Right Post-Emergent Herbicide for Your St. Augustine Lawn
St. Augustine grass makes a beautiful, thick lawn. But weeds love to invade it! Post-emergent herbicides kill weeds that have already popped up. Selecting the right one is key to keeping your turf healthy. This guide helps you make the best choice.
Key Features to Look For
When shopping for a herbicide, check the label closely. You need products made specifically for St. Augustine grass.
- **St. Augustine Safety:** This is the most important feature. Many strong weed killers will damage or kill St. Augustine grass. Look for labels that clearly state “Safe for use on St. Augustine Grass.”
- **Targeted Weed Control:** Does it kill the weeds you see most often? Common lawn invaders include dollarweed, clover, and broadleaf weeds. Ensure the herbicide lists your target weeds.
- **Speed of Action:** How fast does it work? Some herbicides kill visible weeds in just a few days. Others take longer.
- **Systemic vs. Contact:** Systemic herbicides travel through the entire weed, killing the roots. Contact killers only burn the parts they touch. Systemic options usually offer better long-term control.
Important Materials and Ingredients
The active ingredients determine what the product kills and how safe it is for your grass.
Read the ingredient list. Common safe active ingredients for St. Augustine grass include **2,4-D**, **Dicamba**, and sometimes **Quinclorac** (use Quinclorac carefully and check the label for St. Augustine tolerance).
Avoid products containing **Atrazine** or high concentrations of **2,4-DP** unless they are specifically formulated for your grass type. These ingredients often harm St. Augustine.
Factors That Improve or Reduce Quality
The quality of the herbicide depends on how well it works without hurting your lawn.
Factors that Improve Quality: High-quality products often contain a mix of several active ingredients. This broadens the range of weeds they control. Also, liquid concentrates generally offer more precise mixing and better coverage than granular products.
Factors that Reduce Quality: Poor quality shows up in two ways. First, if the product burns your St. Augustine grass, it’s too strong or not meant for your lawn. Second, if it only kills the top of the weed but the roots survive, the weed comes right back. Always use the recommended mixing ratios. Over-concentrating the mix reduces quality by damaging your turf.
User Experience and Use Cases
How easy is the product to use? Good user experience means simple mixing and clear application instructions.
Easy Application: Ready-to-spray containers are often best for beginners. They skip the measuring step. For large lawns, you might prefer concentrates mixed in a large sprayer.
Timing is Everything: The best use case for these products is when weeds are actively growing. Apply herbicides when temperatures are mild, usually between 60°F and 85°F. Applying when it is too hot (over 90°F) or too cold reduces effectiveness and increases the risk of grass injury.
Post-Rain Waiting Period: Wait a few days after rain before applying. The herbicide needs dry leaves to stick to and absorb properly.
10 Frequently Asked Questions (FAQ) About Post-Emergent Herbicides for St. Augustine Grass
Q: Can I use any weed killer on my St. Augustine grass?
A: No. St. Augustine grass is sensitive. You must use products labeled as “safe” or specifically for St. Augustine turf.
Q: How soon after I mow can I apply the herbicide?
A: Wait at least two days after mowing. Mowing stresses the grass, and applying chemicals right after can cause burn spots.
Q: Will this kill my beautiful St. Augustine grass if I mix it wrong?
A: Yes. If you use too much product (over-apply), you risk significant chemical burn or death to your lawn. Always measure carefully.
Q: What is the best temperature to spray post-emergent herbicide?
A: The ideal temperature range is usually 65°F to 85°F. Avoid spraying if temperatures are expected to go over 90°F that day.
Q: Do I need to water the lawn before or after applying the herbicide?
A: The lawn should be slightly moist, but not soaking wet, before application. Do not water for at least 24 hours after spraying so the chemicals can soak in.
Q: How long until I see the weeds dying?
A: Depending on the product and the weed type, you should see visible yellowing or wilting within 3 to 7 days.
Q: Is it better to use a liquid or a granular herbicide?
A: Liquids often provide better, more even coverage, especially for tough, broadleaf weeds. Granules are easier for beginners but need even spreading to avoid streaks.
Q: What if the product only lists “Centipede Grass” but not “St. Augustine Grass”?
A: Do not use it. If St. Augustine is not listed as safe, assume it will harm your lawn. Stick to clearly labeled products.
Q: Can I apply fertilizer and herbicide on the same day?
A: It is generally safer to separate these applications by about one week. This reduces stress on the grass.
Q: How often can I safely apply this type of herbicide?
A: Follow the label instructions strictly. Most products recommend waiting 3 to 4 weeks between treatments to allow the grass time to recover fully.