Quackgrass vs Crabgrass: How to Tell the Difference and Treat Each

Quackgrass and crabgrass look similar at a glance — both are coarse, light-green grasses that stand out in a tall fescue lawn — but they’re completely different weeds with completely different solutions. Crabgrass is a summer annual that dies with the first frost and can be prevented with pre-emergent. Quackgrass is a perennial that survives winter, spreads through underground rhizomes, and laughs at the pre-emergents that stop crabgrass cold. If you’ve been treating what you think is crabgrass and it keeps coming back stronger each year, you’re probably dealing with quackgrass — and everything you’ve been doing is wrong for it.

Quick Overview: The Critical Difference

	Crabgrass	Quackgrass
Life cycle	Summer annual — dies each winter	Perennial — survives year after year
When it appears	June through first frost	March through November
How it spreads	Seeds only (one plant = thousands of seeds)	Seeds + aggressive underground rhizomes
Pre-emergent works?	Yes — very effective	No — it’s already established, not germinating from seed
Post-emergent options	Yes — selective herbicides exist	Very limited — no selective herbicide kills quackgrass without killing desirable turf
Pulling it out	Easy — shallow roots, comes out clean	Difficult — rhizomes break off and regrow
Root system	Fibrous, shallow, annual	Deep, extensive rhizome network (perennial)

If you remember one thing from this guide, make it this: crabgrass can be prevented; quackgrass must be killed. They share a visual resemblance but require opposite treatment strategies.

How to Identify Crabgrass

Crabgrass (Digitaria species, primarily smooth crabgrass and large crabgrass in Missouri) is a warm-season annual that germinates in late spring when soil temperatures reach 55–60°F for several consecutive days. It grows rapidly through the summer and produces thousands of seeds before dying with the first hard frost in October or November.

Crabgrass Identification Checklist

• Germination timing: Emerges in May–June in Missouri, 3–4 weeks after soil temperatures reach 55°F at a 2-inch depth. You’ll notice crabgrass appearing after your spring pre-emergent has worn off or after dandelions have already flowered.
• Growth habit: Low, spreading, with stems that radiate outward from a central point like spokes on a wheel. Individual plants can reach 12–18 inches across in a single season if unmowed.
• Leaf appearance: Light green to yellowish-green, wider than desirable turf (¼ to ½ inch wide), with fine hairs visible on both the upper and lower leaf surfaces. Smooth crabgrass — the common type in St. Charles County — has only a few hairs near the leaf base. Large crabgrass is noticeably hairier.
• Seed heads: Appear in July–August as finger-like spikes radiating from the top of the stem — typically 3–5 spikes per stem, resembling a turkey foot. Each plant produces 150,000+ seeds.
• Stems: Flattened, often tinged with purple at the base, branching freely at the lower nodes where stems touch the soil.
• Roots: Shallow, fibrous, easy to pull. Crabgrass comes out with a satisfying “pop” when pulled by hand — the entire root ball releases from the soil.
• What it looks like at a distance: Thin, spreading patches of lighter green that seem to appear overnight in late spring. Often concentrated along driveway edges, sidewalk cracks, and thin areas of the lawn where grass cover is sparse.

When You’ll See Crabgrass

• May: First tiny seedlings emerge in thin or bare areas, especially near pavement where the soil warms faster
• June–July: Rapid growth and spread — this is when crabgrass becomes most visible
• August–September: Seed head production at full speed
• October–November: Plants die with the first hard frost, turning brown and collapsing

How to Identify Quackgrass

Quackgrass (Elymus repens, formerly Agropyron repens) is a cool-season perennial grass that looks like a coarser, uglier version of the desirable turf it invades. Unlike crabgrass, quackgrass survives Missouri winters and actually grows more aggressively in the cool, moist conditions of spring and fall — the same conditions that favor tall fescue.

Quackgrass Identification Checklist

• Emergence timing: Green and growing before crabgrass has even germinated. You’ll see quackgrass in March–April, often while the surrounding lawn is still waking up from winter. It also stays green later into fall than crabgrass, which dies with the first frost.
• Growth habit: Upright to slightly arching, forming distinct clumps that are noticeably taller than the surrounding turf. Does NOT sprawl outward like crabgrass on creeping stems. Plants reach 12–36 inches tall if unmowed.
• Leaf appearance: Blue-green to grayish-green, ¼ to ½ inch wide, with a rough, sandpapery texture when you run your fingers from tip to base (against the grain). Smooth when rubbed in the other direction. Leaves twist slightly at the tip.
• Auricles (the tell-tale sign): The most reliable identification feature — quackgrass has narrow, white, claw-like appendages (auricles) that wrap around the stem at the base of each leaf blade. Crabgrass has NO auricles. If you peel back a leaf blade and see small white claws gripping the stem, it’s quackgrass.
• Rhizomes (underground stems): Dig up a clump and examine the roots. Quackgrass has sharp-pointed, yellowish-white underground stems (rhizomes) that travel horizontally and send up new shoots at intervals — each rhizome tip is sharp enough to pierce through a potato, which is how quackgrass earned the nickname “witch grass.” Crabgrass has no rhizomes.
• Seed heads: Slender, upright spikes 2–6 inches long that appear May–July. The spikelets are arranged flat against the stem in two alternating rows — unlike crabgrass’s finger-like seed head arrangement.
• Roots: Deep, tenacious, and connected by the rhizome network. Pulling on a quackgrass clump often snaps the stem off at the base, leaving the rhizomes intact underground. Each broken rhizome fragment can produce a new plant.
• What it looks like at a distance: Taller, bluish-green clumps scattered throughout the lawn, often in patches that expand outward from the edges each year as the rhizome network spreads underground.

When You’ll See Quackgrass

• March–April: Quackgrass greens up early — often before the desirable turf — making it easy to spot. This is the best time to map infestations.
• May–July: Seed head production and continued rhizome spread
• August: Slows during summer heat but does NOT die — it just stops growing
• September–November: Resumes active growth in cool fall weather, may look green and healthy while crabgrass is dead
• December–February: Dormant but alive — the rhizomes survive underground

Side-by-Side Comparison Table

Identification Feature	Crabgrass	Quackgrass
When does it first appear?	Late May–June	March–April
When does it die?	First hard frost (Oct/Nov)	Doesn’t die — goes dormant in winter, regrows each spring
Growth direction	Flat, spreading, wheel-spoke pattern	Upright, clumping, taller than turf
Leaf color	Light green to yellowish-green	Blue-green to grayish-green
Leaf texture	Hairy or sparsely hairy, soft	Rough, sandpapery when rubbed backward
Leaf width	¼–½ inch	¼–½ inch
Auricles (claws at leaf base)	None	Present — white, claw-like
Rhizomes (underground stems)	None	Present — sharp-pointed, yellowish-white
Root depth	Shallow (2–4 inches)	Deep (6–12+ inches via rhizomes)
Pulls out easily?	Yes — shallow roots release cleanly	No — stem snaps, rhizomes remain and regrow
Seed head shape	Finger-like spikes (3–5 per stem)	Single slender spike with alternating rows
Seed head timing	July–August	May–July
Seeds per plant	150,000+	25–400 per seed head (fewer, but rhizome spread compensates)
Pre-emergent works?	Yes — very effective	No — it’s perennial, already established
Selective post-emergent exists?	Yes — quinclorac, fenoxaprop, mesotrione	No — nothing kills quackgrass without killing desirable cool-season turf
Mowing impact	Thrives under low mowing	Weakened but not killed by low mowing

The Simple Field Test

If you’re standing on your lawn looking at a patch of coarse, light-colored grass and you can’t tell which weed it is, do these three things in 30 seconds:

1. Check the calendar. If it’s March, April, or early May, and the weed is already full-size and growing, it’s quackgrass. Crabgrass hasn’t germinated yet.
2. Pull on it. Grab a clump near the base and pull steadily. If it slides out of the soil easily with a shallow root ball, it’s crabgrass. If the stem snaps off at ground level and you feel resistance from something still anchored below, it’s quackgrass.
3. Look for auricles. Peel back a leaf blade at its base where it meets the stem. If you see two small white claws gripping the stem, it’s quackgrass. No claws = crabgrass or another weed.

How to Control Crabgrass

Crabgrass is the more straightforward of the two weeds to control because it’s an annual that must start from seed each year — stop the seed from germinating, and you stop the weed.

Pre-Emergent Prevention (Primary Method)

Apply a pre-emergent herbicide in early spring, before crabgrass seeds germinate:

• Timing: When soil temperatures reach 50–55°F at a 2-inch depth for 3–5 consecutive days. In St. Charles County, this typically falls between mid-March and early April. Forsythia bloom is the old-fashioned phenological indicator — when the yellow flowers appear, crabgrass is about to germinate.
• Active ingredients: Prodiamine (Barricade), dithiopyr (Dimension), or pendimethalin (Pendulum). Dithiopyr provides the added benefit of early post-emergent activity on very young crabgrass seedlings.
• Duration: Most pre-emergents provide 3–5 months of control. For season-long protection in Missouri (where crabgrass can germinate through August), a split application — half in March and half in June — provides more consistent coverage than a single dose.
• Application: Apply evenly, water in with 0.25–0.5 inches of irrigation within 48 hours, and avoid disturbing the soil afterward (no aeration or aggressive raking).

Post-Emergent Treatment (If You Already Have It)

If crabgrass is already growing in your lawn:

• Young crabgrass (1–3 leaf stage): Quinclorac (sold as Drive XLR8 or in combination products) or mesotrione (Tenacity) are effective. The younger the plant, the better the kill. Treat in June.
• Mature crabgrass (tillering stage, July–August): Fenoxaprop (Acclaim Extra) provides more reliable control on larger plants. Two applications 10–14 days apart are often needed for complete kill. Mature crabgrass is much harder to kill — it’s worth treating early rather than waiting.
• September: By now the plants are producing seed. Post-emergent treatment provides cosmetic improvement but won’t prevent next year’s crop — the seeds are already in the soil. Focus on cultural practices and plan for next year’s pre-emergent.

Cultural Prevention

• Mow at 3.5–4 inches for tall fescue. Taller grass shades the soil surface and reduces crabgrass germination — crabgrass seeds need light to trigger germination.
• Water deeply and infrequently. Light daily watering creates perfect crabgrass conditions at the soil surface. Deep, weekly watering favors deep-rooted turf over shallow-rooted crabgrass.
• Maintain dense turf. Bare spots and thin areas are crabgrass magnets. Overseed thin areas in fall to build turf density.

How to Control Quackgrass

Quackgrass is the harder weed. Because it’s a perennial grass with rhizomes — and because it’s closely related to desirable turfgrasses — there is no selective herbicide that kills quackgrass in a tall fescue or Kentucky bluegrass lawn without also killing the desirable grass. Every control method requires some sacrifice of surrounding turf.

Method 1: Non-Selective Spot Treatment (Most Effective)

This is the standard recommendation from university extension services including the University of Missouri and University of Illinois:

1. Apply glyphosate (Roundup or generic equivalent) directly to quackgrass clumps. Use a foam paintbrush, sponge, or shielded sprayer to apply glyphosate to quackgrass leaves only — minimize contact with surrounding desirable turf.
2. Timing is critical: Apply in fall (September–October) or early spring (March–April) when quackgrass is actively growing but desirable cool-season turf may be semi-dormant. Fall applications are more effective because the plant is translocating nutrients (and the herbicide) down into the rhizomes for winter storage.
3. Wait 7–10 days: The quackgrass will yellow and die. Resistant clumps may need a second application.
4. Dig out dead material and prepare the bare spot for reseeding or sodding.
5. Overseed the treated area with desirable grass seed (late summer through September is ideal in Missouri). The glyphosate has no soil activity, so seeding can begin as soon as the treated plants are removed — typically 7 days after application.

What to expect: You will kill a patch of grass — probably 6–18 inches across depending on the size of the quackgrass clump. The surrounding turf will fill in from the edges over time, but overseeding accelerates recovery and prevents new weeds from colonizing the bare soil.

Method 2: Smothering (For Large Infestations)

If quackgrass covers a significant area — a patch 10 feet across, or multiple interconnected patches — glyphosate spot-treatment may be impractical. For large areas:

1. Mow the area as short as possible.
2. Cover with black plastic or thick cardboard weighted down at the edges.
3. Leave covered for 4–6 weeks during active growing season (May–September). The combination of heat, darkness, and lack of water will kill both the quackgrass and the desirable turf.
4. Remove the cover, till or rake the dead material, and reseed or sod.
5. Solarization works best in full sun during July–August. Shaded areas take longer; consider glyphosate instead.

Method 3: Repeated Mowing Suppression (Partial Control Only)

You cannot mow quackgrass to death — the rhizomes store enough energy to regrow repeatedly. But consistent, frequent mowing (every 3–4 days at 2–3 inches during active growth) can weaken the plant over time by forcing it to constantly expend energy replacing leaf tissue rather than expanding its rhizome network. This is a suppression strategy, not an eradication strategy, and it works best when combined with aggressive fertilization and watering of the desirable turf to outcompete the weakened quackgrass.

What Does NOT Work on Quackgrass

• Pre-emergent herbicides: Quackgrass is perennial. It doesn’t germinate from seed each year — it regrows from established rhizomes. Pre-emergents that stop crabgrass by preventing seed germination have no effect on quackgrass.
• Selective grassy-weed herbicides: Products containing quinclorac, fenoxaprop, or mesotrione that work on crabgrass provide little to no control of quackgrass. The plant is too closely related to the desirable turf.
• Hand-pulling: You’ll remove the above-ground foliage, but every rhizome fragment left in the soil will regrow. Hand-pulling without digging out the rhizomes typically makes the problem worse by breaking the rhizome network into multiple new plants.
• Vinegar, boiling water, or salt: Home remedies burn the foliage but don’t reach the rhizomes. The plant regrows from underground reserves within 2–3 weeks.

The Bottom Line: When to Treat What

Situation	It’s Crabgrass If…	It’s Quackgrass If…
Appears in March–April	❌ Too early	✅ Quackgrass greens up before crabgrass germinates
Appears in June	✅ Crabgrass germination window	❌ Quackgrass already full-grown by June
Spider-like spreading pattern	✅ Crabgrass sprawls from a central point	❌ Quackgrass grows upright in clumps
Dies completely in winter	✅ Crabgrass is an annual	❌ Quackgrass rhizomes survive underground
Pulls out easily	✅ Crabgrass has shallow roots	❌ Quackgrass stem snaps, rhizomes stay put
Sharp-pointed underground stems	❌	✅ Quackgrass rhizomes
Hairy leaves	✅ Crabgrass leaves are hairy	❌ Quackgrass leaves are smooth but rough-textured
White claws at leaf base	❌ No auricles on crabgrass	✅ Distinctive quackgrass auricles
Responds to pre-emergent	✅ Crabgrass germination can be stopped	❌ Established quackgrass isn’t affected
Responds to quinclorac	✅ Effective on crabgrass	❌ No effect on quackgrass
Gets worse every year	❌ Crabgrass is annual — start fresh each year	✅ Quackgrass rhizome network expands annually

When to Call a Professional

If you’ve been through this guide and concluded that you have quackgrass — especially if it covers more than a few scattered clumps — professional help is worth the investment. Spot-treating quackgrass with glyphosate and then restoring the treated areas with new turf is tedious, exacting work. Getting the timing right matters — fall treatments hit the rhizomes harder, and the overseeding window is narrow.

A professional lawn care provider can:

• Map and treat all quackgrass infestations in one pass with commercial-grade equipment
• Time the treatment for maximum rhizome kill (fall applications)
• Prep the treated areas and overseed with a grass variety matched to your lawn
• Set up a maintenance program that builds turf density to suppress future invasion

For crabgrass, a professional can apply properly timed split pre-emergent applications — the spring + early-summer schedule that provides season-long control with fewer breakthroughs than a single spring application typically delivers.

If you’re seeing grassy weeds you can’t identify, or if your crabgrass treatments haven’t been working (which might mean you’re actually fighting quackgrass), request a quote and ask for a lawn evaluation. A local provider who knows Missouri turf will identify exactly what you’re dealing with in the first visit.