St. Augustine grass is a warm-season turf popular in southern regions for its lush appearance and shade tolerance. However, it can be sensitive to certain herbicides. That’s why choosing the best post emergent weed killer for St. Augustine is essential to eliminate unwanted weeds without damaging your lawn.
Post emergent weed killers are applied after weeds have sprouted. These products are designed to kill existing broadleaf and grassy weeds while preserving the health of your established turf. In this guide, we review the top-rated post emergent herbicides that are safe for St. Augustine grass.
We evaluate product performance, active ingredients, application methods, and weed spectrum. Whether you’re targeting crabgrass, clover, or dollarweed, these options provide effective, lawn-safe control. Let’s explore the best post emergent herbicides formulated for St. Augustine lawns.
Top 10 Best Post Emergent Weed Killers for St. Augustine Grass
1. Southern Ag 2,4-D Amine Weed Killer
This selective herbicide controls broadleaf weeds without harming St. Augustine. It’s highly effective on clover, chickweed, and dandelion. Use with care during hot weather.
Mixes easily and covers large areas. Apply with a sprayer for even coverage. Affordable and widely available solution for home use.
Recommended for spring and early summer. Works quickly on contact. One of the most trusted products for Southern lawns.
- Fast-acting
- Cost-effective
- Broad coverage
- Easy to mix
- Safe formula
- Trusted brand
- Effective results
- Strong odor
- Weather sensitive
- Needs dilution
2. Spectracide Weed Stop for Lawns
This ready-to-spray option targets over 200 types of weeds. It’s formulated for Southern grasses, including St. Augustine. Convenient hose-end attachment simplifies application.
Kills weeds down to the root within hours. Safe when used as directed. Great for large lawns with a variety of weeds.
Visible results appear fast. No mixing required. Excellent for beginner gardeners.
- Easy use
- Quick results
- No dilution
- Broad coverage
- Southern-safe
- Large area
- Convenient design
- Plastic nozzle
- Single-use sprayer
- Strong smell
3. Ortho Weed B Gon Chickweed, Clover & Oxalis Killer
Specially designed to eliminate stubborn broadleaf weeds. Safe for use on St. Augustine and other southern turfs. Visible results appear in 1–2 days.
Best applied during active weed growth. Covers wide area efficiently. Won’t harm your lawn when used correctly.
Available in different sizes. Consistent results reported. Great choice for spot treatments.
- Fast action
- Multi-use
- Large coverage
- St. Augustine safe
- Easy to use
- Trusted brand
- Targeted formula
- May require repeat
- Limited availability
- Strong chemical
4. Hi-Yield Atrazine Weed Killer
A trusted formula for post emergent control of tough weeds. Atrazine is safe on St. Augustine when used at label rates. Controls dollarweed and poa annua effectively.
Apply using a pump or hose sprayer. Ideal for spring and early summer application. Can also prevent new weed growth.
Effective in shady areas. Long-lasting control. Use cautiously in high temperatures.
- Long-lasting
- Wide spectrum
- Prevention too
- Easy application
- St. Augustine safe
- Highly rated
- Best for spring
- Can stain
- Strict timing
- Requires care
5. Fertilome Weed-Out Lawn Weed Killer
Offers broad control with three active ingredients. Selective and gentle on St. Augustine. Works well against dandelions, plantains, and chickweed.
Apply on calm, dry days for best results. Economical choice with concentrated formula. Great for treating visible weed patches.
Mixes easily in sprayers. Can be stored safely. Works on warm-season grasses.
- Triple action
- Safe formula
- Cost effective
- Easy mixing
- Visible results
- Targeted control
- Large coverage
- Needs weather care
- Slow on some
- Mixing needed
6. BioAdvanced Southern Weed Killer for Lawns
Formulated especially for Southern grasses like St. Augustine and Centipede. Controls clover, dollarweed, and oxalis. Rainproof in just 1 hour.
Easy to use with ready-to-spray packaging. Starts working on contact. Trusted brand for weed control in sensitive lawns.
Perfect for warm climates. Won’t harm turf. Affordable and accessible.
- Rainproof fast
- Easy spray
- Safe formula
- Brand trust
- Good coverage
- Southern turf safe
- Visible results
- Plastic sprayer
- Short shelf life
- Less effective cold
7. Roundup for Lawns (Southern Formula)
This Roundup version is safe for St. Augustine and Southern grasses. Controls 90+ weeds including crabgrass and nutsedge. Won’t harm your lawn when applied correctly.
Easy-to-use trigger or hose-end sprayers available. Fast results in as little as 3 hours. Good choice for broad-spectrum control.
Provides long-lasting weed management. Ideal for Southern homeowners. Versatile application methods.
- Quick effect
- Broad spectrum
- Trusted brand
- Sprayer options
- Southern safe
- Long lasting
- Multi-use
- Costly
- Not organic
- Can irritate skin
8. Bonide Weed Beater Southern Lawns
Effective against broadleaf and grassy weeds common in Southern lawns. Designed for use on St. Augustine, Bahia, and Bermuda. Works in cool and warm weather.
Rainproof shortly after application. Best used during early weed growth stages. Provides visible results in under a week.
Compact bottle is easy to store. Coverage is efficient per ounce. Best used with sprayer.
- Quick rainproof
- Cool weather use
- Efficient coverage
- Safe on Southern
- Fast results
- Works on many
- Easy storage
- Strong smell
- Some weeds resist
- Needs follow-up
9. Gordon’s SpeedZone Southern Herbicide
A professional-grade solution with fast-acting formula. Safe for use on Southern turf varieties like St. Augustine. Controls over 100 weed types.
Ideal for warm and transitional zones. Starts showing results within 24 hours. Requires careful mixing for best results.
Works well for large areas. Common among landscapers. Recommended for thick infestations.
- Pro-level strength
- Quick result
- Wide spectrum
- Southern turf safe
- Ideal for pros
- Great coverage
- Efficient mix
- Mix carefully
- Pricey
- Can overapply
10. Image Herbicide for St. Augustine Grass
Specially developed for tough weeds in St. Augustine lawns. Controls sedge, dollarweed, and more. Safe to use during most of the growing season.
Apply with a sprayer and water in lightly. Avoid using during extreme heat. Provides long-lasting weed suppression.
Effective on sedges. Trusted by Southern homeowners. Best used early in season.
- Sedge control
- Season-long use
- Southern safe
- Trusted brand
- Easy to apply
- Long-lasting
- Good coverage
- Heat sensitive
- Slow results
- Not all weeds
7 Best Post Emergent Weed Killer For St Augustine FAQs
1. Will post emergent herbicides kill my St. Augustine grass?
Only if you use the wrong kind. Choose herbicides labeled safe for St. Augustine to avoid damage.
2. When is the best time to apply post emergent weed killer?
Apply when weeds are actively growing, typically spring through early fall. Avoid extreme heat and drought.
3. How long should I wait to mow after application?
Wait at least 2–3 days after treatment before mowing. This allows the herbicide to fully absorb.
4. Can I use a post emergent on newly seeded lawns?
No—wait at least 6–8 weeks after seeding before applying any herbicide.
5. What weeds are controlled?
Products vary, but most control clover, chickweed, dollarweed, crabgrass, and dandelion. Read the label carefully.
6. Do I need to reapply?
Some weeds require multiple treatments. Follow label directions for timing and frequency.
7. Should I water after applying?
Some products need to be watered in; others should dry on the leaf surface. Check instructions for specifics.
Conclusion
Finding the best post emergent weed killer for St. Augustine grass ensures effective control without harming your lawn. Choose a product specifically labeled for use on Southern turfgrass.
The Southern Ag 2,4-D Amine Weed Killer is the best overall due to its affordability and effectiveness on common weeds. The Spectracide Weed Stop for Lawns is a strong runner-up for its ease of use and broad-spectrum performance.
Apply at the right time and follow all label directions for the best results. Protect your St. Augustine lawn while eliminating unsightly weeds. With the right product, your grass will thrive weed-free all season long.