Fall Pre-Emergent: Which Pre-Emergent Is Best for Fall? (Warm-Season & Cool-Season Lawns)
Hey y’all —
Every Yard Mastery program generally recommends pre-emergent weed control in both spring and fall, unless you’re seeding. That means our warm-season programs and a lot of you cool-season folks who aren’t seeding this fall get the fall pre-emergent recommendation.
Which Pre-Emergent is Best for Fall?
It depends on your grass type. Warm-season lawns get two applications: Prodiamine first, then Dimension a few weeks later. Cool-season lawns that aren’t seeding get one application of Dimension.
Fall Pre-Emergent in a Nutshell
- What we’re stopping: Poa annua (annual bluegrass) is the big one, along with other fall-germinating weeds like spurge, hairy bittercress, chickweed, and henbit.
- When: These weeds start germinating as soil temps fall to around 70°F. Get your pre-emergent down before that. Early is fine. Late is not ideal.
- Warm-season lawns (Bermuda, St. Augustine, Zoysia, Centipede, Bahia): 2 fall applications. Fall 1 is Prodiamine. Fall 2 is Dimension, a few weeks later.
- Cool-season lawns that are NOT seeding (tall fescue, Kentucky bluegrass, ryegrass): 1 fall application of Dimension, on the same day as your fertilizer.
- Seeding this fall? Skip pre-emergent. It stops grass seed too.
👉 Shop every option in one place: Pre-Emergents
Why Fall Pre-Emergent Matters: Poa Annua and Winter Weeds
The weed everyone fights in fall is Poa annua. You won’t even notice it at first. It germinates in fall, hides out small, and shows up as those bright green clumps around January or February. Then it rages into spring and drops its seed when the heat shows up, which sets you up for the same fight next year.
It doesn’t come alone. Spurge, hairy bittercress, chickweed, and henbit all germinate in this same window. On a cool-season lawn, you may not see any of them until next spring, but they’re already in the soil waiting.
A pre-emergent works by stopping these seeds before they germinate. It won’t do anything to a weed that’s already growing, which is why timing is everything.
When to Apply Pre-Emergent in Fall
These weeds start germinating as soil temperatures fall to around 70°F coming out of summer. Your pre-emergent needs to be down before that happens.
- Early is fine.
- Late is not ideal. Once they germinate, a pre-emergent can’t stop them.
Don’t guess at soil temps. The Yard Mastery App tracks soil temps for your zip code and tells you when to throw’er down.
Warm-Season Lawns: Two Fall Pre-Emergent Applications
Bermuda, St. Augustine, Zoysia, Centipede, and Bahia get two fall pre-emergent applications. Think of it as two coats of paint.
Fall Pre-Emergent #1: Prodiamine (Granular or WDG)
Your first fall app is Prodiamine, the same pre-emergent we use in spring. If you’ve got leftovers in the garage, use them up.
You’ve got two ways to put it down:
- Prodiamine granular (0-0-7): spread it with your broadcast or rotary spreader. The label rate is 3 lbs per 1,000 sq ft. The 18 lb bag covers 6,000 sq ft, and the 45 lb bag covers 15,000 sq ft.
- Prodiamine WDG Drop-N-Go Packs: our new WDG, or “water-dispersible granule”. It comes in pre-measured packets built for a 4-gallon backpack sprayer. Drop one packet into 4 gallons of water, and you’ve covered 4,000 sq ft. There’s no weighing and no measuring. (It’s for backpack or pump sprayers, not hose-end.)
Mixing a partial packet or using the 5 lb bottle? The step-by-step is here: How to Apply Prodiamine 65 WDG.
In the Yard Mastery App, Fall 1 on your warm-season plan pairs this with your fertilizer and Compaction Cure, so it’s one trip across the lawn. The full Fall 1 and Fall 2 program is in Warm Season Fall Lawn Care for Bermuda, Zoysia & St. Augustine.
Fall Pre-Emergent #2: Dimension (Dithiopyr), a Few Weeks Later
About 30 days after Fall 1, you’ll apply your second coat of pre-emergent: Dimension. Dimension is the brand name for the active ingredient dithiopyr, and ours is a granular. It stops the same weeds as Prodiamine but goes after them a little differently, especially Poa annua. That’s why we switch products for the second app instead of doubling up. It is also what we use when Prodiamine’s yearly max is used up.
Dimension goes down with a broadcast or rotary spreader on a dry lawn. The label rate is 3–4 lbs per 1,000 sq ft. The 18 lb bag covers up to 6,000 sq ft and the 45 lb bag up to 15,000 sq ft.
Cool-Season Lawns (Not Seeding): One Fall Pre-Emergent Application with Fertilizer
Tall fescue, Kentucky bluegrass, and ryegrass lawns get one fall pre-emergent app. Apply it on the same day as your fall fertilizer, Flagship 24-0-6 (or whatever fall fertilizer your Yard Mastery program recommends). Apply them separately, not mixed in your spreader, because you won’t get even coverage that way.
Get it down in early fall.
Important: this is ONLY for lawns that are not being seeded this fall. Pre-emergent stops grass seed from germinating, just like it stops weeds. If you’re seeding or overseeding, skip it and follow the seeding path in the app.
The full no-seed fall program is in Cool Season Fall Lawn Care Without Seeding.
Kentucky Bluegrass & Ryegrass: Dimension
We use Prodiamine in spring. The catch is that Prodiamine has a yearly maximum on the label, and for Kentucky bluegrass and ryegrass that max is usually used up by your spring apps. (The granular label caps KBG and perennial rye at 6.0 lbs per 1,000 sq ft per year, and our spring split app uses 3 lbs per 1,000 each time.)
So for fall, KBG and rye lawns switch to Dimension, spread on the same day as Flagship.
Tall Fescue: A Third Prodiamine Application or Dimension
Tall fescue gets more leeway on the Prodiamine label (up to 9.0 lbs per 1,000 sq ft per year on the granular), so you can make a 3rd Prodiamine application this fall if you have a 100% tall fescue lawn. Or you can apply Dimension in the fall at the higher rate of 4 lbs per 1,000 sq ft like KBG and rye lawns.
100% tall fescue lawns: choose 1 for the fall:
- Granular: Prodiamine 0-0-7, apply at 3 lbs per 1,000 sq ft with a spreader on the same day as your Flagship (or app-recommended fertilizer). Apply individually, not mixed in the spreader, to ensure even coverage.
- Granular: Dimension, apply at 4 lbs per 1,000 sq ft with a spreader on the same day as your Flagship (or app-recommended fertilizer). Apply individually, not mixed together in the spreader, to ensure even coverage.
- Liquid: Prodiamine WDG Drop-N-Go Packs. One packet in a 4-gallon backpack sprayer covers 4,000 sq ft. You can tank-mix Spoon Juice or Compaction Cure into the same sprayer, so you walk the lawn just once.
Pre-Measured Prodiamine Packets: See How It Works
In this video, I show you the pre-measured Prodiamine WDG packets: drop one in a 4-gallon backpack sprayer, and you’re ready to cover 4,000 sq ft.
Fall Pre-Emergent at a Glance
| Lawn | Fall apps | What to use | When | Goes down with |
|---|---|---|---|---|
| Warm-season (Bermuda, St. Augustine, Zoysia, Centipede, Bahia) | 2 | Fall 1: Prodiamine (granular or WDG). Fall 2: Dimension |
Fall 1: before soil temps fall to ~70°F. Fall 2: 30 days later. |
Fall 1: fertilizer + Compaction Cure, per your app plan |
| Kentucky bluegrass/ryegrass (NOT seeding) | 1 | Dimension | Early fall | Flagship, same day |
| Tall fescue (NOT seeding) | 1 | 3rd Prodiamine app (granular or WDG) or Dimension | Early fall | Flagship, same day. WDG can tank-mix with Compaction Cure. |
| Any lawn being seeded this fall | 0 | No pre-emergent | — | Follow the seeding path in the app |
Prodiamine vs. Dimension, the short version: both stop Poa annua and the other winter annuals before they germinate. Prodiamine is our spring and first-fall product, in granular or WDG. Dimension (dithiopyr) is granular, goes after the same weeds a little differently (especially Poa), and is what we use when Prodiamine’s yearly max is used up.
Shop Fall Pre-Emergents
- All Pre-Emergents
- Prodiamine WDG Drop-N-Go Packs (pre-measured, 4,000 sq ft per packet)
- Prodiamine 0-0-7 Granular
- Dimension (Dithiopyr) 0-0-7 Granular
- Flagship 24-0-6 Fertilizer (cool-season, same day as your pre-emergent)
- 4-Gallon Backpack Sprayer
Fall Pre-Emergent FAQ
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Wrapping Up
Fall pre-emergent is one of those jobs you’ll thank yourself for in February, when your neighbor’s lawn is polka-dotted with Poa, and yours isn’t. Warm-season folks: Prodiamine, then Dimension a few weeks later. Cool-season folks who aren’t seeding: one app on the same day as Flagship, with Dimension for KBG, fescue, and rye.
Not sure when to apply? Open the Yard Mastery App, check your calendar, and then throw’er down!
I’ll see you in the lawn,
Allyn, The Lawn Care Nut
