Is This Crabgrass? The Complete Visual Identification Guide

Something in your lawn doesn’t match the rest — grass that looks different from the rest of the lawn, whether it’s coarser, taller, a different shade of green, or spreading in a pattern you’ve never seen before. If you’re asking "what kind of grass is this?" you’re not alone. Before you reach for a bottle of weed killer, stop. The wrong treatment won’t just fail — it can damage your lawn and waste an entire season. Correctly identifying what’s growing in your yard is the single most important step toward fixing it.

This guide covers the six most common grassy weeds and lookalikes you’ll encounter in the Sioux Falls area, complete with photos, hands-on field tests, and the key features that tell them apart.

Quick-Reference Identification Chart

Use this chart as a starting point. Find the row that best matches what you’re seeing, then scroll down to the detailed section for confirmation.

Crabgrass — The Warm-Season Annual Everyone Knows in Sioux Falls, SD

Crabgrass is probably the most well-known lawn weed in America — and for good reason. This warm-season annual thrives in the heat of summer, growing low to the ground in a distinctive flat, star-shaped pattern. Each plant radiates outward from a central point, which is why it’s sometimes called “finger grass.”

How to Identify Crabgrass

• Leaves: Light green, wider than your lawn grass, with a pointed tip and tiny hairs along the blade edges and sheaths
• Stems: Reddish-purple at the base, lying flat against the ground before turning upward
• Growth pattern: Flat and spreading — hugs the ground and branches outward like a star or crab legs
• Height: Low-growing (2–6 inches), much shorter than surrounding turf when unmowed
• Root system: Shallow, fibrous roots — pulls up easily with a tug

Growth Stages to Watch For

Seedling (late May–June): Small, upright blades that are easy to miss. Slightly lighter green than surrounding grass. This is the easiest stage to control.

Mid-summer (July–August): Now clearly visible as flat, spreading clumps. The star-shaped growth pattern is unmistakable. Each plant can produce thousands of seeds.

Mature (September): Seed heads form at the tips of the stems — thin, finger-like spikes radiating from a central point. The plant has already deposited next year’s seeds into the soil.

After frost: Crabgrass is a true annual — it dies completely at the first hard frost, turning brown and leaving behind bare patches where it crowded out your lawn. Those patches become prime real estate for next year’s crabgrass seeds.

Clumping Tall Fescue — The #1 Most Misidentified “Weed”

Here’s an important distinction: clumping tall fescue isn’t actually a weed. It’s a perfectly legitimate grass species — it’s just growing where it doesn’t visually belong. When a few tall fescue plants pop up in a fine-bladed Kentucky bluegrass lawn, they stick out like a sore thumb and get mistaken for weeds.

How to Identify Tall Fescue Clumps

• Leaves: Wide, dark green blades — noticeably wider and coarser than the surrounding bluegrass
• Surface: The top of each blade is shiny and smooth. Run your finger along it — you’ll feel the difference from the matte finish of bluegrass
• Texture: Coarse and rough to the touch — feels like rubbing a thick ribbon between your fingers
• Growth pattern: Bunch-type (clumping) growth. Each plant forms a distinct, round clump rather than spreading through runners
• Root system: Deep, fibrous root ball. No rhizomes — it doesn’t spread underground

Why Tall Fescue Shows Up in Your Lawn

Tall fescue spreads exclusively by seed. Seeds blow in from neighboring lawns, roadsides, or even older plantings on your own property. Some lawns were originally seeded with a tall fescue mix years ago, and individual clumps persist while the rest of the lawn has transitioned to bluegrass through overseeding.

Because tall fescue is a cool-season perennial, it’s green year-round — which means it’s often one of the first things you notice in spring when it’s already lush while your bluegrass is still waking up. This early green-up is another reason people mistake it for a weed.

Quackgrass — Aggressive, Perennial, and Hard to Kill

If crabgrass is the most well-known lawn weed, quackgrass is the most frustrating. This cool-season perennial spreads aggressively through underground rhizomes, survives winter, and laughs at most herbicides. It’s one of the hardest grassy weeds to eliminate from a lawn.

How to Identify Quackgrass

• Leaves: Blue-green, flat, and wider than most lawn grasses (about ¼ inch). The blade surface feels like sandpaper when you run your finger along the top
• Auricles: This is the definitive ID feature. At the base of each leaf where it meets the stem, quackgrass has small, claw-like appendages that clasp around the stem — like tiny arms hugging it. No other common lawn weed has this
• Height: Grows taller than your lawn — often the first grass you notice sticking up above everything else after mowing
• Seed head: Produces a distinctive spiked seed head (similar to wheat) in late spring through summer
• Root system: Thick, white, underground rhizomes that spread laterally. Any fragment left in the soil will regrow into a new plant

The auricle test: Gently peel back a leaf from the stem. If you see small, finger-like projections clasping around the stem at the junction, it’s quackgrass. This single feature is the most reliable way to confirm identification.

Why Quackgrass Is So Hard to Control

Those thick white rhizomes are the problem. They spread laterally underground, sending up new shoots every few inches. When you try to pull quackgrass, the rhizomes snap — and every fragment left behind generates a new plant. Mowing doesn’t faze it. Broadleaf herbicides ignore it. It survives winter, drought, and heavy traffic. The only reliable control methods are non-selective spot treatment or extremely thorough manual removal.

Goosegrass — The Flat Weed That Loves Compacted Soil

Goosegrass is frequently confused with crabgrass, but the two are actually quite different when you know what to look for. While crabgrass spreads in a loose star pattern, goosegrass forms a tight, flat rosette that’s pressed firmly against the ground — almost like it’s been stepped on.

How to Identify Goosegrass

• Growth pattern: Extremely flat rosette, radiating from a central point. Looks like a compressed wagon wheel
• Center: Silvery-white or whitish at the very base — this is the single best way to distinguish it from crabgrass
• Leaves: Dark green (darker than crabgrass), flat, and folded along the midrib
• Stems: Flattened and whitish-green at the base
• Seed head: Two to six finger-like spikes radiating from a central point, similar to crabgrass but thicker
• Preferred habitat: Compacted soil — driveways edges, sidewalk cracks, high-traffic paths, sports fields

The Compaction Connection

If you’re seeing goosegrass, it’s telling you something about your soil. This weed almost exclusively invades areas with compacted soil — places where foot traffic, vehicles, or heavy equipment have compressed the ground. Healthy, loose soil with good grass coverage rarely has goosegrass problems. Addressing the compaction through core aeration is often more effective than any herbicide.

Annual Bluegrass (Poa Annua) — The Bright Green Spring Deceiver

Annual bluegrass — known by its scientific name Poa annua — is one of the sneakiest lawn invaders because it looks so similar to desirable grass. In fact, it’s closely related to Kentucky bluegrass. But it’s a weedy annual that creates bright light-green patches in your lawn every spring, then dies in the summer heat, leaving thin or bare spots behind.

How to Identify Annual Bluegrass

• Color: Bright apple-green — noticeably lighter and more vivid than the surrounding lawn, especially in early spring
• Leaf tip: Boat-shaped or canoe-shaped — the tip of each blade folds upward like the bow of a boat. This is the most reliable ID feature
• Seed heads: Produces small, whitish seed heads even when mowed very short. You’ll see them scattered across the lawn surface in spring
• Height: Low-growing, forming small clumps or patches at or below mowing height
• Texture: Fine-bladed, similar to Kentucky bluegrass — which is why it blends in until the color difference gives it away
• Lifecycle: Germinates in late summer or fall, grows through winter and spring, then dies when summer heat arrives. It returns each year from the massive seed bank it deposits in your soil

Where to Look

Annual bluegrass favors shaded areas, low spots that stay moist, and overwatered lawns. You’ll often see it along the north side of buildings, under trees, and in areas where irrigation runs too frequently. Unlike crabgrass (which loves sun and heat), Poa annua thrives in cool, moist conditions.

Foxtail — The Fuzzy Seed Head Weed

Foxtail is hard to miss once it produces its signature seed head — a soft, fuzzy, cylindrical spike that looks exactly like a miniature fox’s tail. It’s a summer annual that often appears in lawns where pre-emergent coverage has broken down or where the turf is thin and stressed.

How to Identify Foxtail

• Seed head: The unmistakable feature — a dense, bristly, cylindrical spike, typically 1–4 inches long. Green foxtail has a slightly drooping head; yellow foxtail’s is more upright and compact
• Growth habit: Upright, growing 1–3 feet tall if left unmowed. Much more vertical than crabgrass
• Leaves: Medium green, flat at the base, with a slight twist. Blades are wider than most lawn grasses
• Stems: Round and smooth, often branching from the base
• Root system: Fibrous and shallow — pulls up relatively easily

Common Types in the Sioux Falls Area

Green foxtail is the most common variety in South Dakota lawns. It produces a slightly nodding seed head and grows more aggressively in warm weather. Yellow foxtail is shorter with a more compact, upright seed head and has a distinctive tuft of long hairs at the base of each leaf. Giant foxtail can reach 3–5 feet tall in unmowed areas and has the largest seed heads of the three.

Foxtail typically shows up in mid to late summer, particularly in lawns that were seeded in spring (pre-emergent herbicide can’t be used on newly seeded areas) or where pre-emergent applications have worn off. Like crabgrass, it’s an annual that dies at frost — but the seeds it drops will be waiting to germinate next year.

How to Confirm What You Have — Field Tests That Work

Photos are helpful, but hands-on tests are often the fastest way to confirm what’s growing in your lawn. Here are four simple field tests you can do right now.

The Touch Test

• Sandpaper texture on top of the blade → Quackgrass
• Tiny hairs along the blade edges → Crabgrass
• Smooth and shiny on top → Clumping tall fescue
• Waxy and smooth, folded along the center → Goosegrass
• Fine-textured with boat-shaped tips → Annual bluegrass

The Pull Test

• Thick white rhizomes come up with the plant → Quackgrass (and any fragment left behind will regrow)
• Shallow fibrous roots, pulls up easily → Crabgrass or foxtail
• Deep, dense root ball that resists pulling → Clumping tall fescue
• Flat rosette lifts from the surface → Goosegrass

The Season Test

• Visible before your lawn fully greens up in spring → Cool-season perennial (quackgrass or tall fescue) or cool-season annual (Poa annua)
• Appeared in summer heat (June–August) → Warm-season annual (crabgrass, goosegrass, or foxtail)

The Growth Pattern Test

• Flat, spreading star shape → Crabgrass
• Extremely flat rosette, pressed to the ground → Goosegrass
• Upright, distinct clumps → Clumping tall fescue or foxtail
• Spreading patches that keep expanding outward → Quackgrass
• Light green patches at mowing height → Annual bluegrass

Why Correct Identification Matters

Misidentifying a grassy weed doesn’t just mean using the wrong product — it can mean wasting an entire growing season while the problem gets worse. Here’s why it matters:

• Selective broadleaf herbicides don’t work on grassy weeds. Products containing 2,4-D, dicamba, or triclopyr are designed to kill dandelions, clover, and other broadleaf weeds. They have zero effect on crabgrass, quackgrass, tall fescue, or any other grass-type weed. Spraying them is a waste of product and time.
• Pre-emergent timing depends on which weed you’re targeting. Crabgrass pre-emergent goes down in early spring. Annual bluegrass pre-emergent goes down in fall. Apply at the wrong time and you’ll miss the germination window entirely.
• Some “weeds” can only be removed physically. Clumping tall fescue and quackgrass can’t be selectively sprayed — the only options are digging them out or spot-treating with non-selective products that also kill your lawn grass.
• Misidentification is the #1 reason homeowners think their treatment “isn’t working.” If you’re treating for crabgrass but the problem is actually quackgrass, no amount of pre-emergent will help — quackgrass is a perennial that spreads through rhizomes, not seeds.

For a deeper dive into why lawn treatments sometimes seem to fail, read our guide on why you might still be seeing “crabgrass” after treatment.

What to Do Once You’ve Identified It

Now that you know what’s in your lawn, here’s the quick version of what comes next:

• Crabgrass, goosegrass, foxtail, or annual bluegrass: These are annuals. Prevention with properly timed pre-emergent herbicides is the most effective strategy. Existing plants can be spot-treated or will die naturally at frost (or in summer heat, for Poa annua).
• Quackgrass: Requires non-selective spot treatment or thorough manual removal including all rhizomes. Plan to reseed treated areas afterward.
• Clumping tall fescue: Dig out individual clumps and fill with desirable seed, or spot-treat and reseed.

For detailed removal methods, timing calendars, and long-term prevention strategies for each of these weeds, read our companion guide: How to Get Rid of Crabgrass and Grassy Weeds.

Let Sharp Lawn Care Handle It

Identifying and controlling grassy weeds takes knowledge, timing, and the right products. Sharp Lawn Care’s weed control and fertilization program includes professionally timed pre-emergent and post-emergent applications throughout the growing season — so you don’t have to guess at timing or products.

Serving the Sioux Falls metro including Brandon, Harrisburg, Tea, and surrounding communities. Call (605) 251-6880 or Get a Free Quote to get started.