Key Takeaways
- Different weeds, different treatments: Crabgrass is annual (dies in winter). Quackgrass is perennial (survives year-round). Using the wrong herbicide wastes money and time.
- The rhizome test: Pull up the plant. White underground runners = quackgrass. Shallow fibrous roots only = crabgrass. This 30-second test is definitive.
- Pre-emergent only works on crabgrass: It prevents seeds from germinating. Quackgrass spreads via rhizomes, not seeds, so pre-emergent does nothing.
- Quackgrass is harder to kill: No selective herbicide exists. Options are spot-treating with glyphosate or lawn renovation.
- Timing matters: Crabgrass appears in late spring/summer heat. Quackgrass is visible year-round, especially noticeable in spring when it greens up before your lawn.
Crabgrass vs Quackgrass
How to Tell Them Apart & Why It Matters
These two grassy weeds get confused constantly, and it costs homeowners real money. Apply pre-emergent for quackgrass? Wasted product. Spray crabgrass killer on quackgrass? Nothing happens. Pull quackgrass thinking it's crabgrass? You just made it spread. Getting the ID right is the first step to actually solving the problem.
Quick Comparison at a Glance
| Characteristic | Crabgrass | Quackgrass |
|---|---|---|
| Scientific Name | Digitaria spp. | Elymus repens |
| Life Cycle | Annual (dies each winter) | Perennial (lives for years) |
| Root System | Shallow, fibrous roots | Deep rhizomes (underground runners) |
| Growth Habit | Low, spreading, crab-like | Upright, aggressive clumps |
| Leaf Width | Wide (1/4" - 1/3") | Narrow to medium (1/8" - 1/4") |
| Leaf Color | Light green to yellow-green | Blue-green to gray-green |
| Peak Season | Summer (June-September) | Year-round (most visible spring) |
| Seed Heads | Finger-like spikes (3-7) | Wheat-like spike |
| Pre-emergent Works? | Yes | No |
| Selective Herbicide? | Yes (quinclorac, fenoxaprop) | No (glyphosate only) |
| Control Difficulty | Moderate | Very Difficult |
| Hand Pulling? | Effective if done before seeding | Makes it worse (spreads rhizomes) |
Why Does Correct Identification Matter?
Crabgrass and quackgrass require completely different control strategies. The wrong treatment wastes money and allows the weed to spread while you wait for results that never come.
Last summer, a homeowner called me frustrated. He'd applied pre-emergent religiously for three years, yet "crabgrass" kept coming back. One look at his lawn told the story: quackgrass. Three years of wasted pre-emergent, hundreds of dollars, and the problem was actually getting worse because the quackgrass had three years to spread its rhizome network unchallenged.
Wrong ID = Wasted Effort
- Pre-emergent on quackgrass = $0 benefit
- Quinclorac on quackgrass = nothing happens
- Pulling quackgrass = spreads it faster
- Waiting for quackgrass to "die in winter" = it won't
Correct ID = Effective Treatment
- Pre-emergent prevents 95%+ of crabgrass
- Quinclorac kills emerged crabgrass selectively
- Glyphosate spot-treatment kills quackgrass
- Proper timing for each weed's lifecycle
How Do You Visually Tell Them Apart?
Crabgrass grows low and spreads outward like a crab. Quackgrass grows upright in clumps. Crabgrass has wide, light-green blades. Quackgrass has narrower, blue-green blades with clasping auricles.
Images: Wikimedia Commons
Crabgrass Appearance
- Growth: Flat, spreading outward from center (crab-like)
- Blades: Wide (1/4" to 1/3"), pointed tips
- Color: Light green to yellow-green, lighter than lawn
- Texture: Coarse, may have fine hairs
- Seed heads: 3-7 finger-like spikes radiating from stem tip
- Height: Stays low (2-6") unless unmowed
Quackgrass Appearance
- Growth: Upright, forms aggressive clumps
- Blades: Narrower (1/8" to 1/4"), tapered tips
- Color: Blue-green to gray-green, duller than lawn
- Texture: Rough on upper surface, smooth below
- Seed heads: Single wheat-like spike
- Height: Grows tall quickly (often first to need mowing)
- Auricles: Small claw-like projections clasp the stem at leaf base
What's the Definitive Root Test?
Dig up a suspect plant with a trowel. Crabgrass has shallow fibrous roots. Quackgrass has thick, white, underground rhizomes that spread horizontally. This test is 100% accurate.
When visual ID leaves doubt, the root test settles it. This takes 30 seconds and is completely definitive.
Dig Around the Plant
Use a trowel or knife to cut a circle around the weed, about 3-4 inches from the center. Go at least 4 inches deep.
Lift and Examine
Lift the soil plug and shake off loose dirt. Look at what's attached to the plant below the surface.
Check for Rhizomes
Quackgrass has thick (1/8" diameter), white, fleshy underground stems running horizontally. They look like white roots but are actually stems with visible nodes. Crabgrass has only thin, fibrous roots with no horizontal runners.
Crabgrass Roots
- Shallow, fibrous root system
- No underground runners
- Roots at stem nodes where touching soil
- Easy to pull up entirely
- Tan/brown colored roots
Quackgrass Roots/Rhizomes
- Deep, extensive rhizome network
- White, fleshy horizontal stems underground
- Sharp, pointed growing tips
- Can spread 3-5 feet per season
- Breaking rhizomes creates new plants
How Do You Control Crabgrass?
Prevention with pre-emergent herbicide in early spring is 95%+ effective. For emerged crabgrass, post-emergent herbicides containing quinclorac or fenoxaprop kill it without harming lawn grass.
Crabgrass control is straightforward once you know you actually have crabgrass. The annual lifecycle is the key weakness to exploit.
Prevention (Best Approach)
Pre-emergent herbicide creates a chemical barrier in soil that kills crabgrass seedlings as they germinate.
- Timing: Apply when soil reaches 55°F for 3-5 days (forsythia bloom)
- Products: Prodiamine (Barricade), Dithiopyr (Dimension), Pendimethalin
- Duration: One application lasts 3-4 months; split apps extend coverage
- Success rate: 95%+ when timed correctly
For complete pre-emergent guidance, see our crabgrass control guide.
Post-Emergent Treatment
For crabgrass that's already growing, selective herbicides kill the weed without harming desirable grass.
- Quinclorac: (Drive XLR8) Most effective, works on young and mature crabgrass
- Fenoxaprop: (Acclaim Extra) Professional product, excellent results
- Timing: Best when crabgrass has 1-4 tillers (before it spreads wide)
- Multiple apps: Mature crabgrass may need 2-3 treatments
Cultural Control
- Mow high: 3-4" grass height shades soil, preventing germination
- Thick lawn: Dense turf leaves no room for crabgrass
- Hand pulling: Effective for small patches before seed heads form
- Let it die: First frost kills all crabgrass; prevent next year's crop
How Do You Control Quackgrass?
No selective herbicide kills quackgrass in lawns. Options are spot-treating with glyphosate (kills grass too), repeated mowing stress, or full lawn renovation. Complete elimination is difficult.
Here's the hard truth about quackgrass: it's one of the most difficult lawn weeds to eliminate. No product kills quackgrass while leaving your lawn grass alive. Your options range from "manage it" to "start over."
Glyphosate Spot Treatment
Non-selective herbicide (Roundup) kills quackgrass but also kills any grass it touches.
- Method: Paint or carefully spray individual clumps
- Timing: Fall is best (plant moving nutrients to roots)
- Wait time: 7-14 days until completely dead
- Follow-up: Reseed or sod the dead spots
- Repeat: New shoots from missed rhizomes need retreatment
Lawn Renovation
For severe infestations, starting over is sometimes the most practical option.
- Kill everything: Broadcast glyphosate over entire area
- Wait: 2 weeks for complete kill
- Till or remove: Optional, but helps remove rhizome mass
- Wait again: Let any surviving rhizomes sprout, treat again
- Reseed or sod: Start fresh with clean soil
Suppression (Not Elimination)
If you can't eliminate it, you can slow it down:
- Frequent mowing: Weakens plants over time by depleting reserves
- Thick lawn: Healthy grass competes better
- Never pull: Broken rhizomes multiply the problem
- Solarization: Black plastic over patches in summer (6-8 weeks)
What Mistakes Make These Weeds Worse?
The biggest mistake is misidentification leading to wrong treatment. Second is pulling quackgrass (spreads rhizomes). Third is expecting pre-emergent to work on established perennial weeds.
Pulling Quackgrass
Every broken rhizome piece becomes a new plant. A single pull can create 5-10 new plants from rhizome fragments left behind.
Pre-Emergent for Quackgrass
Pre-emergent prevents seed germination. Quackgrass spreads primarily via rhizomes, not seeds. Complete waste of product.
Crabgrass Killer on Quackgrass
Products like quinclorac are specifically designed for crabgrass. They have zero effect on quackgrass. Different plant, different chemistry.
Waiting for Winter to Kill Quackgrass
Quackgrass is perennial. It goes dormant in winter but survives underground. It will green up again in spring, often before your lawn does.
Tilling Quackgrass Areas
Tilling chops rhizomes into pieces, and each piece grows. Tilling can turn a patch into a field-wide infestation.
Letting Crabgrass Go to Seed
One crabgrass plant produces up to 150,000 seeds. Letting it seed replenishes the soil seed bank for years of future problems.
Quick Decision Guide
Frequently Asked Questions
Can I use the same herbicide for crabgrass and quackgrass?
No. Crabgrass and quackgrass require completely different herbicides. Pre-emergents work on crabgrass but not quackgrass. Post-emergent crabgrass killers (quinclorac) don't affect quackgrass. Quackgrass requires glyphosate spot treatment or renovation.
Why did pre-emergent fail to stop my grassy weed?
If your grassy weed returned despite pre-emergent, you likely have quackgrass, not crabgrass. Quackgrass is perennial and spreads via underground rhizomes. Pre-emergent only prevents seed germination, so it has no effect on established quackgrass.
Which is worse for lawns, crabgrass or quackgrass?
Quackgrass is harder to eliminate because it's perennial and spreads underground. Crabgrass dies each winter, so consistent pre-emergent use can eliminate it in 2-3 years. Quackgrass persists indefinitely and often requires lawn renovation to fully remove.
Can I pull crabgrass and quackgrass by hand?
Pulling works for crabgrass if you get the whole plant before it seeds. Pulling quackgrass is counterproductive. Every broken rhizome fragment left in soil grows into a new plant. Pulling quackgrass typically makes infestations worse.
What's the fastest way to identify which weed I have?
Dig up a plant and check the roots. Crabgrass has shallow, fibrous roots with no runners. Quackgrass has white, fleshy underground rhizomes that spread horizontally. The rhizome test is definitive and takes 30 seconds.
Do crabgrass and quackgrass grow in the same areas?
They can coexist but prefer different conditions. Crabgrass thrives in thin, hot, sunny areas and dies in winter. Quackgrass tolerates shade better, survives winter, and often invades from field edges or neglected areas.