I tested five products I rely on to control weeds around St. Augustine lawns — from ready-to-spray weed & feed to surfactants and a spray dye that keeps me precise. Here’s what I use, when I use it, and which options to避
I manage several yards with St. Augustine grass and know how easy it is for broadleaf weeds and fungal issues to take hold. Over multiple seasons I tested a mix of treatments and add-ons so I could recommend practical combos that actually work in that turf.
My approach: avoid anything labeled unsafe for St. Augustine, use selective herbicides or spot treatments when needed, and add a surfactant or spray indicator to improve accuracy. Below I walk through the products I kept returning to, and how I use each one.
I organized these picks by role: products that directly treat weeds, those that boost spray performance, and tools that prevent over-application. Keep in mind: some popular "weed and feed" granules are explicitly not for St. Augustine, so I call that out where relevant and recommend alternatives or safe uses based on what I saw in the field.
1. Scotts Turf Builder Weed & Feed – Best Dual-Action (Not for St. Augustine)
I like this weed-and-feed for thickening and broadleaf control on compatible grasses, but I do not use it on St. Augustine because the label warns against it.
Why I picked it: It combines lawn food with broadleaf control for lawns it’s labeled for.
Best for: Homeowners with non‑St. Augustine turf who want one-step feed and weed control.
Good coverage per bag for the cost; applied with a broadcast spreader.
Pros
- Feeds while killing a range of weeds
- Targets 50+ listed broadleaf weeds
- Covers a large area per bag
- Easy to apply with a spreader
Cons
- Not safe for St. Augustinegrass
- Only apply when grass is wet and 60–90°F
- Limited to two applications per year
My take
I used this product on a bermuda lawn and saw the expected thickening and decline in clover and dandelion after following the spreader settings. The granules stick best to damp grass, so I either work with morning dew or lightly water before application.
Because the label explicitly forbids use on St. Augustine, I never apply this on the turf this roundup focuses on. For lawns that are listed as compatible (bahiagrass, bermuda, zoysia, etc.), the dual-action formula saved me time by delivering fertilizer and weed control in one pass.
Application timing matters: I stop watering for 24 hours after treatment and avoid applying if rain is expected. When used on the appropriate grass types, the product gave noticeable results within a few weeks and reduced the need for spot spraying later in the season.
2. Southern Ag Non-Ionic Surfactant – Best Spray Adjuvant
I add this non‑ionic surfactant to selective herbicide mixes to improve coverage and penetration on broadleaf weeds without changing the herbicide itself.
Why I picked it: It reduces surface tension so herbicides spread and stick better.
Best for: Anyone mixing herbicides for targeted spot treatment or lawn-wide sprays.
A concentrated pint that lasts through multiple treatments.
Pros
- Improves spray coverage and penetration
- Compatible with many herbicides
- Concentrated — multiple uses per bottle
Cons
- Not a herbicide on its own
- Always confirm compatibility on your herbicide label
My take
I keep this pint on the shelf whenever I’m spraying selective herbicides near my St. Augustine stands. Adding the recommended rate made my spray mix cling to leaf surfaces and improved knockdown on broadleaf targets.
Because it’s non‑ionic, I found it easy to mix with 2,4‑D formulations and other tank mixes I use for spot work. The product’s main value for me is that it increases consistency — less beading, more even contact.
I always check the primary herbicide label before adding a surfactant. When used correctly, this adjuvant reduced the need to reapply in areas where spray coverage had been uneven.
3. Liquid Harvest Lazer Blue Spray Indicator – Best Spray Pattern Indicator
I add this concentrated blue dye to my spray tank to see exactly where I’ve applied herbicide and to avoid double‑spraying St. Augustine turf.
Why I picked it: Makes spray lines and drift visible so I can be precise.
Best for: Anyone spraying liquid herbicides who wants to avoid overlap and drift.
A little concentrate goes a long way; economical for repeated use.
Pros
- Makes sprayed areas easy to see
- Helps prevent over-application
- Mixes easily into sprayers
Cons
- Can stain if spilled
- Bottle measurement can be awkward
My take
I never spray herbicide without a pattern indicator now. The vivid blue shows up on grass and bare ground, which makes it simple to identify missed strips or places I’ve already covered.
On bright green St. Augustine I can still spot the dye, especially when I look from a distance or wear polarized sunglasses. That visibility saved me from double-applying in several tight areas around flower beds.
Be careful when pouring and mixing — the dye will spread if you spill, and some bottle styles make measuring fiddly. Despite that, the time and product savings from avoiding overlap make it worth having in my kit.
4. Scotts DiseaseEx Lawn Fungicide – Best for Lawn Disease
I reach for this fungicide when brown patch or other turf diseases threaten my St. Augustine; it acts quickly and provides several weeks of control.
Why I picked it: Controls many lawn diseases and starts working fast.
Best for: Lawns showing early fungal symptoms or at risk from disease.
A bit more investment but treats a substantial area per bag.
Pros
- Controls 26 named lawn diseases
- Begins working within 24 hours
- Provides up to four weeks control
Cons
- May need repeat treatments
- Not a weed control product
My take
When I first saw brown patch developing in a shady corner of my St. Augustine, I applied this product per the preventative/curative spreader settings. Within a couple of weeks the patch stopped expanding and new grass began to fill in at the edges.
I followed a schedule of repeat applications at 14–28 day intervals where needed, and the lawn improved noticeably over a month. This product is a good tool in my disease‑management rotation — just don’t expect it to kill weeds.
Application timing is key: I start treatments when conditions favor disease rather than waiting until the problem is severe. Used as directed, it gives me confidence the turf is protected during hot, humid stretches.
5. Spectracide Weed & Feed Ready-to-Spray – Best Ready-to-Spray
I rely on this hose-end ready-to-spray when I want a fast, no-fuss application that feeds the lawn while tackling many common broadleaf weeds.
Why I picked it: Very easy to apply with a hose-end sprayer for large areas.
Best for: Homeowners who prefer a quick, spray-and-go solution.
Convenient ready-to-spray format offers solid value for big yards.
Pros
- QuickFlip hose-end sprayer
- Feeds lawn while addressing broadleaf weeds
- Treats large areas per bottle
Cons
- Some stubborn weeds require repeat treatments
- Effects take several weeks to appear
My take
I hooked this up and covered a mid-sized yard in a single session — the QuickFlip sprayer made the job easy and fast. I developed a spray pattern and worked methodically to avoid missed strips.
The fertilizer effect showed up after a couple weeks and helped the turf look greener, while many common broadleaf weeds began to bleach and die over the following month. For very stubborn species I followed up with spot treatments.
If you want convenience and decent coverage without mixing, this is the easiest route. Just be patient: these formulas take time to show the full effect.
How I Choose Products for St. Augustine Lawns
Safety for St. Augustine Grass
I always read the label specifically for St. Augustine warnings before buying a weed product. Some broad-spectrum "weed and feed" granules explicitly say not to use on St. Augustine, and I won’t risk it.
When a product is labeled safe for St. Augustine, I still test a small area first if the lawn is new or stressed.
- Look for explicit label approval for St. Augustine or Floratam.
- Avoid products that list St. Augustine in the "Do not use on" section.
- Spot-test a small area if you’re unsure or treating an older, stressed turf.
Selective Herbicide vs. Blanket Treatments
I prefer spot treatment with selective herbicides for patches of broadleaf weeds in St. Augustine and reserve blanket treatments for clearly compatible lawns. This minimizes turf stress.
When broad infestation is present and the product is safe for St. Augustine, a lawn-wide approach can be efficient — otherwise, I combine spot sprays with mechanical removal.
- Use spot sprays for isolated infestations.
- Save blanket weed-and-feed for compatible grass species only.
- Combine cultural practices (mowing, fertilizing correctly) to reduce weed pressure.
Timing and Conditions I Follow
I apply herbicides when weeds are actively growing and when temperatures and humidity fall within the recommended range. For many granules that means daytime temps in the 60–90°F band.
Avoid applying before rain and don’t water for 24 hours after granular treatments that require dry settling.
- Apply when weeds are actively growing for best uptake.
- Avoid application before rain; follow re-entry and watering restrictions.
- For spray mixes, add a non‑ionic surfactant when the label permits to improve contact.
Tools and Add‑ons I Use
A spray pattern indicator dye and a surfactant are the two small items that routinely improve my accuracy and efficacy when spraying around St. Augustine.
A reliable spreader or hose‑end sprayer is worth buying once so you get even coverage and predictable results.
- Pattern indicator dye to avoid overlap and gaps.
- Non‑ionic surfactant to improve herbicide performance where allowed.
- Use the manufacturer’s spreader settings for granules.
Frequently Asked Questions
Can I use weed-and-feed products on St. Augustine grass?
I check labels first: several weed-and-feed granules explicitly forbid use on St. Augustine. If the product label lists St. Augustine in the "Do not use on" section, I do not apply it. For St. Augustine I favor selective spot treatments or products labeled safe for that turf.
Should I add a surfactant when spraying weeds in St. Augustine lawns?
I add a non‑ionic surfactant when the herbicide label permits it. It improves spray coverage and uptake, which is especially helpful for spot applications. I never add it blindly—always confirm compatibility on the herbicide label.
How do I avoid damaging my St. Augustine while spraying?
I use a spray pattern indicator to see exactly where I’ve applied product and work from the outside in on target patches. I also use selective herbicides approved for St. Augustine and avoid blanket treatments with products that list St. Augustine as a restricted grass.
When is the best time to treat weeds or disease in St. Augustine?
I treat weeds when they’re actively growing and when temperatures match product guidance. For disease, I apply preventatively when conditions favor fungal outbreaks, and I follow up with repeat applications per the fungicide directions if needed.
Final Take
Managing weeds in St. Augustine turf is mostly about picking the right tools and applying them carefully. I avoid products that explicitly list St. Augustine as a no‑go and instead rely on selective herbicides plus a surfactant and a spray indicator for precision.
Between targeted herbicide work, disease control where necessary, and a few well-chosen add‑ons, I keep my St. Augustine lawns healthy without overapplying chemicals. Start small, follow the labels, and build a seasonal plan that minimizes stress on the turf.
