Can You Apply Pre-Emergent Weed Killer in Fall? (Here’s When It Works Best)

As the temperatures begin to cool once again, you might wonder, "Can you apply pre-emergent in the fall?" The answer is yes. In fact, it’s one of the best strategies for preventing winter weeds like Poa annua, chickweed, and henbit from invading your lawn. Fall pre-emergent stops weed seeds before they sprout, giving you a cleaner lawn in late winter and early spring. The key is timing your application when soil temperatures reach 70°F and start falling.

In this guide, we’ll cover exactly when and why to apply a fall pre-emergent, the best products for the job, and how it fits into your overall fall lawn care weed control strategy. 

So if you’re serious about keeping your lawn weed-free heading into next spring, keep reading.

Why Fall Is Prime Time for Pre-Emergent Herbicide

Many homeowners think pre-emergent herbicides are just a spring thing. But if you only apply in spring, you’re missing half the battle.

Fall pre-emergent applications are crucial for controlling winter weeds, like Poa annua (annual bluegrass), chickweed, and henbit, which germinate in cooler weather. If these weeds get a foothold in fall, they’ll pop up to ruin your lawn’s look in late winter and early spring.

So, if you’re asking, "Is fall too late for pre-emergent?" The answer depends on timing and conditions, not the calendar.

 

Related: The Ultimate Guide to Fall Weed Control 

 

Common Weeds Controlled by Fall Pre-Emergent Applications:

1. Poa Annua (Annual Bluegrass)

• One of the most notorious lawn weeds.

• Germinates in fall and becomes visible in late winter/early spring.

• Forms unsightly clumps that disrupt uniform turf appearance.

Read more>> How to Get Rid of Poa Annua in Your Lawn

 

2. Chickweed

• Low-growing, mat-forming weed.

• Thrives in cool, moist fall and winter conditions.

• Can spread rapidly if not controlled early.
  
  

3. Henbit

• Member of the mint family with purple flowers.

• Germinates in fall and grows aggressively in early spring.

• Common in thin or stressed lawn areas.

 

Read more>> How to Get Rid of Henbit

 

4. Carolina Geranium (Wild Geranium)

• A cool-season annual that germinates in fall.

• Produces small, pink flowers and can overtake bare spots.

 

Read more>> Lawn Weeds with Pink Flowers 

 

5. Mustard Weeds (Field Mustard, Shepherd’s Purse)

• Broadleaf weeds that germinate in fall.

• Often overlooked until they flower and seed in spring.
  
  

6. Annual Ryegrass (Volunteer Ryegrass)

• Unwanted grassy weed that competes with desirable turf.

• Germinates in fall and disrupts uniform grass texture.

 

Read more>> What Types of Weeds Look Like Grass? 

 

7. Corn Speedwell

• Small, sprawling weed with tiny purple-blue flowers.

• Difficult to control once established; fall pre-emergent prevents germination.

 

Read more>> Which Lawn Weeds Have Purple Flowers? 

 

8. Cressleaf Groundsel (Butterweed)

• Germinates in fall, forms large rosettes.
  Bolts in spring, producing yellow flowers.

 

Related: Which Lawn Weeds Have Yellow Flowers? 

 

When to Apply Pre-Emergent Herbicide in Fall

The soil temperature is your true indicator for fall pre-emergent application, not just flipping the calendar to September.

The Magic Number: 70°F and Falling

You want to apply your pre-emergent when soil temperatures consistently drop to around 70°F and are on a downward trend. This is typically late August through early October, depending on where you live.

Why 70°F? Because that’s when weed seeds start to think about germinating. You want your pre-emergent barrier in place before they get any funny ideas.

 

Related: What are Pre-emergent Herbicides and When Should You Apply Them? 

 

Best Pre-Emergent for Fall Applications

When it comes to fall lawn herbicides, Prodiamine and Dithiopyr are the top dogs. Both provide excellent pre-emergent weed control, but they have different strengths:

1. Prodiamine 0-0-7 Pre-Emergent with Fertilizer

• Great for long-lasting control

• Safe for most warm-season grasses

• Also feeds your lawn while preventing weeds

 

prodiamine-38-pre-emergent-herbicide-with-fertilizer-0-0-7-50lb

 

2. Dimension (Dithiopyr) 0-0-7 Pre-Emergent with Fertilizer

• Slightly shorter residual than Prodiamine, but has early post-emergent control for young weeds

• Excellent choice if you’re slightly late on application.

 

dimension-15-pre-emergent-herbicide-with-fertilizer-0-0-7

 

If you're only doing one fall pre-emergent application, Prodiamine is your go-to. But if you're running a little behind schedule, Dimension can catch early germinators slipping through.

No-Fertilizer Pre-Emergent Options

If you’ve already fertilized and just want pre-emergent protection without extra nutrients, Specticle® FLO Pre-Emergent Herbicide and Prodiamine 65 WDG are top-tier choices.

Specticle® FLO Pre-Emergent Herbicide (For Warm-Season Lawns Only)

 

specticle-flo-pre-emergent-herbicide

 

What Is It?

Specticle® FLO is a liquid pre-emergent herbicide containing Indaziflam (7.4%). It is designed specifically for warm-season grasses like Bermuda, Zoysia, Centipede, and St. Augustine.

You apply it as a spray — no fertilizer included — making it a clean, high-performance option for fall weed prevention.

Why It’s Ideal if You Don’t Want Fertilizer

Specticle® FLO contains no nitrogen, phosphorus, or potassium, so it won’t interfere with any fertilizer you’ve already applied. It’s pure, targeted weed control with no nutrient overlap.

What It Controls

Specticle® FLO provides broad-spectrum control of over 60 grassy and broadleaf weeds, including:

• Poa annua (annual bluegrass)
  
  

• Chickweed
  
  

• Henbit
  
  

• Goosegrass
  
  

• Crabgrass (including early post-emergent control)
  
  

• Spurge, oxalis, cudweed, and more

It’s especially effective against Poa annua, making it one of the strongest fall pre-emergents for warm-season lawns.

How to Apply It (Fall Timing)

• Mix with water and apply using a backpack or battery-powered sprayer.
  
  

• Apply in late summer to early fall, when soil temps begin dropping below 70°F.
  
  

• Be precise — Specticle® FLO is powerful and requires accurate rate calibration.

• 0.15 to 0.225 fl oz per 1,000 sq ft, depending on turf type and desired length of control. One 18 oz bottle covers up to ~130,000 sq ft.

• Water in with 0.25 to 0.5 inches of irrigation or rainfall within 24–48 hours to activate the barrier.

Prodiamine 65 WDG (Brand Alternative to Barricade®)

 

prodiamine-65-wdg-brand-alternative-barricade%C2%AE-65wdg

What Is It?

• This is a water-dispersible granule (WDG) formulation containing 65% Prodiamine.
  
  

• You mix it with water and spray it — no need for additional fertilizer. It’s purely pre-emergent.

Why It’s Ideal if You Don’t Want Fertilizer

• Contains no nitrogen or phosphorus — just the active ingredient — so it won’t interfere with your existing fertilization plan.

What It Controls

• Targets both grass and broadleaf annual weeds: Poa annua (annual bluegrass), henbit, chickweed, knotweed, foxtail, goosegrass, and more.

How to Apply It (Fall Timing)

• Mix in a backpack or battery sprayer — heavy agitation is needed to keep the product suspended.
  
  

• Apply 5.2 g per 1,000 sq ft in early fall (when soil temperatures are dropping below ~70°F), offering about three months of protection.
  
  

• Water in with up to ½″ of irrigation or rain within 24–48 hours to activate the barrier.

 

Fall Pre-Emergent Application Guide (Step-by-Step)

Alright, let’s get into the how-to of fall pre-emergent application:

Step 1: Check Soil Temperature (Not Air Temperature)

Before you grab your spreader, you need to know if the soil is ready. Weed seeds don’t care what the calendar says; they germinate based on soil temperatures.

• Target Soil Temp: 70°F and falling. This is the sweet spot when weeds like Poa annua start to germinate.
  
  

• Don’t Rely on Air Temperatures: Air temperatures fluctuate wildly and don’t reflect the conditions underground. Soil temperatures matter.

How to Check Soil Temperature:

• Use a soil thermometer (probe 2-4 inches into the soil for accuracy).
  
  

• You can track soil temperatures online using soil temperature maps specific to your zip code.

Pro Tip: Start monitoring soil temps in late August. Be ready to apply when you see 70°F soil temps for 3-5 consecutive days.

Step 2: Mow Your Lawn Before Application

Mowing right before application ensures your pre-emergent granules can reach the soil surface, where they need to form a barrier.

• Mowing Height: Trim your lawn to about 1/3 of its normal height.
  
  

• Why It Matters: Tall grass can block granules from reaching the soil, weakening your weed control.

Pro Tip: Bag or rake up cuttings after mowing. You don’t want excessive debris interfering with the application.

Step 3: Apply Pre-Emergent Granules with a Broadcast Spreader

This is the step where precision pays off.

• Equipment: Use a quality broadcast spreader for even coverage.
  
  

• Application Rate: Follow the product label, but most fall pre-emergents recommend 2.5 to 4 lbs per 1,000 sq ft.
  
  

• Prodiamine 0-0-7: Around 3 lbs per 1,000 sq ft.
  
  

• Dimension 0-0-7: Similar rates, with flexibility for light post-emergent needs.

Application Tips:

• Walk at a consistent pace to avoid overapplying or missing spots.
  
  

• Use a criss-cross pattern (apply half the rate north-south, half east-west) for thorough coverage.

Pro Tip: Load the spreader on a driveway or tarp to catch spills and avoid wasting product on unintended areas.

Step 4: Water It in to Activate the Barrier

Pre-emergent herbicides need water to move into the top layer of soil and create that invisible weed barrier.

• Irrigation amount: Apply 0.25 to 0.5 inches of water after spreading.
  
  

• Light irrigation ensures the granules dissolve and bind to soil particles.
  
  

• Natural rainfall: If rain is forecast (within 48 hours), you can let Mother Nature handle it — but make sure it’s light to moderate rain, not a downpour.

Pro Tip: Avoid overwatering. Heavy watering can push the herbicide too deep, where it becomes ineffective.

Step 5: Avoid Disturbing the Soil Post-Application

Once your pre-emergent is in place, you want that barrier to stay intact.

• No core aeration or dethatching: Aerating or dethatching after applying pre-emergent will punch holes in the barrier, allowing weeds to sneak through.
  
  

• Minimize raking and foot traffic: Heavy raking, aggressive weeding, or even frequent foot traffic can disrupt the protective layer.
  
  

Pro Tip: If you plan to aerate your lawn, do it before applying pre-emergent. Always protect the barrier once it's established.

What About Fall Weed Spraying (Post-Emergent)?

Pre-emergent handles seeds. But what if weeds are already popping up?

That’s where post-emergent herbicides come in.

Recommended Post-Emergents for Fall:

1. Celsius and Certainty Herbicide Kit

• Safe for all warm-season grasses other than Bahia

• Controls over 180 grassy and broadleaf weeds

• Kills all sedges (nutsedge, kyllinga, annual, and globe)

• Effective against Poa annua (annual bluegrass)

• Safe to apply over a broad temperature range

• Kit covers 72,000-130,000 square feet

• Kit includes two herbicides, plus a surfactant and marker dye.

 

celsius-and-certainty-herbicide-kit-with-surfactant-and-dye

 

2. Tenacity and Sedgehammer Herbicide Kit (For cool-season lawns) 

• Safe for Kentucky Bluegrass, Perennial Ryegrass, Tall and Fine Fescues, and Centipede grass

• Controls over 50 grassy and broadleaf weeds

• Kills sedges (nutsedge, kyllinga, annua,l and globe)

• Kit covers 43,000-87,000 square feet.

• Kit includes two herbicides, plus a surfactant and marker dye.

 

tenacity-and-sedgehammer-herbicide-kit-with-surfactant-and-dye-cool-season-grass

 

If you don’t want to buy a full kit, we have several options for post-emergent herbicides in our store. Just be sure to check the label to ensure it’s safe to use on your turf type and will work against the weed you are tackling.

Post-emergents are best applied when weeds are actively growing. Fall spraying can knock back existing weeds before they go to seed, reducing weed pressure next year.

Fall Lawn Treatment for Weeds: A Seasonal Strategy

Here’s a simple fall weed control calendar to keep you on track:

Common Mistakes to Avoid with Fall Pre-Emergents

1. Waiting too long — If you apply after weeds germinate, pre-emergents won’t help.

2. Not watering it in — Activation requires water. Skipping this step renders it useless.

3. Disturbing the soil barrier — Heavy raking or aerating after application will break the barrier.

4. Using the wrong product for your grass type — Always ensure herbicide compatibility with your lawn type.

 

Related: The Best Spurge Weed Killers That Won't Harm Your Lawn

 

FAQs About Fall Pre-Emergent Application

Can you apply pre-emergent in the fall and spring?

Absolutely! A two-pass strategy (spring + fall) gives you year-round weed control.

Can I apply fall pre-emergent if I recently overseeded my lawn?

If you’ve recently overseeded, avoid applying pre-emergent until the new grass is fully established (usually 6-8 weeks). Pre-emergents prevent all seed germination, including your desired grass seed.

Do I need to apply a fall pre-emergent every year?

Yes, for consistent weed control, annual fall pre-emergent applications are recommended. Skipping a year can allow winter weeds to take over.

How long does fall pre-emergent last?

Prodiamine can provide up to 4 months of residual control, depending on rate and weather.

Should I aerate before or after applying pre-emergent?

Always aerate before applying pre-emergent. Aerating after application will break the weed barrier.

How much rain is too much after applying pre-emergent in fall?

A light rainfall or irrigation of 0.25 to 0.5 inches is ideal. Heavy downpours (1 inch or more) within 24 hours of application can dilute or wash away the barrier, reducing effectiveness. So, check the weather forecast before you apply.

Can I apply pre-emergent to bare soil areas in the fall?

Yes, but be cautious. Pre-emergents will prevent any seeds from germinating, so don’t apply in spots where you plan to seed or repair turf soon after.

Will fall pre-emergent help with crabgrass?

Fall pre-emergent primarily targets cool-season weeds like Poa annua, but it also lays a foundation that can reduce early spring crabgrass outbreaks, especially in milder climates. For more information on how to combat crabgrass, read our blog: The Best Crabgrass Weed Killers That Won't Kill Turfgrass. 

Can I use fall pre-emergent on a newly sodded lawn?

You should wait until the new sod is well-rooted (typically 6-8 weeks) before applying pre-emergent. Applying too soon can stress or damage young turf.

Does applying more pre-emergent in fall give longer weed control?

Not necessarily. Stick to label rates. Overapplying can harm your lawn and is not more effective. For extended control, a split application (early fall + late fall) at labeled rates is better than a heavy single dose.

Should I combine fall pre-emergent with fertilizer applications?

Absolutely. Many products, like Prodiamine 0-0-7 and Dimension 0-0-7, already include fertilizer, making it easy to combine weed control with fall feeding.