What Is Watergrass in a Lawn (ID & Removal)
“Watergrass” is a common name, not a dependable plant ID. In many areas, it means barnyardgrass, a summer annual grass with broad leaves and an open seedhead, but it may refer to other weeds or even a sedge. Check the plant before treating it. Then remove small patches by hand or use a product labeled for both the weed and your lawn’s grass.
If you identify the plant correctly, you can choose a treatment that targets the weed without putting your lawn at needless risk. The steps below help you check the plant, decide whether to pull or treat it, and reduce the chance it returns.
Identify Watergrass and Prepare Equipment Safely
“Watergrass” does not name one species everywhere. It often refers to barnyardgrass, but local use varies. To make a useful identification, inspect several plants and look at the leaf collar, stem base, and seedhead. Also identify your lawn’s turf species before choosing any herbicide.
How to recognize likely barnyardgrass
Barnyardgrass (Echinochloa crus-galli) is a warm-season annual grass. It grows from seed, often in spring or summer, and may stand out from finer lawn grass because its leaves are broad and its growth is coarse. The base of the stem may look flattened or reddish.
Mature plants can develop an open, branched seedhead. A useful clue is the leaf collar, where the blade meets the stem: barnyardgrass typically lacks a visible membranous ligule, a thin flap of tissue found in some grasses. Young plants may not yet have a seedhead, so do not rely on one feature alone.
Compare it with crabgrass and sedge
Crabgrass can also grow in warm weather and form a coarse patch. It usually has a membranous ligule, and some species have hairs on the leaf blade or sheath. Because traits vary with species and growth stage, compare several features rather than using color or size alone.
Yellow nutsedge is not a grass. Its stem is triangular when viewed in cross-section, and its leaves grow in three ranks around the stem. Grass-selective herbicides generally do not control sedges, so mistaking nutsedge for a grass weed can waste treatment and may harm the lawn.
| What you notice | Possible ID clue | What to check next |
|---|---|---|
| Broad leaves, flattened or reddish stem base, open seedhead | Barnyardgrass is possible | Inspect the leaf collar and compare several plants |
| Membranous ligule, sometimes with hairs | Crabgrass is possible | Check the whole plant and local weed guide |
| Three-sided stem, leaves in three ranks | Sedge, such as yellow nutsedge | Do not treat it as a grassy weed |
| Only “watergrass” on a label, video, or note | Not enough to identify it | Confirm the plant and lawn type first |
I would not spray based only on a common name. If the plant is young or the features are unclear, take clear photos of the whole plant, stem base, and leaf collar. Ask a local extension service or qualified turf professional to confirm it before applying a herbicide.
Check the lawn and equipment before work
Find out which turf species you have. Herbicide safety depends on both the weed and the desirable grass. A product that is suitable for one lawn type may injure another, and its label may restrict use by season or site.
For mowing, use a mower in good condition with its guards in place and discharge directed away from people, pets, and desirable plants. Set the deck for your turf species, not for the weed. Tall fescue is commonly maintained around 3–4 inches, but that height is not a universal setting for every lawn. Follow local guidance for your grass type.
Remove or Treat Watergrass in the Lawn
The best control depends on how many plants you have, whether they have formed seedheads, and whether the identification is certain. Pulling can suit a few isolated plants. For widespread growth, choose only a herbicide whose label lists the identified weed, your turf species, and the site.
Step 1: Decide whether to pull or treat
For a small patch, hand-pulling is often the simplest option. Moistened soil can make it easier to remove the crown and roots. The crown is the plant’s base, where stems and roots meet. Pull carefully, then check the spot for remaining pieces or nearby seedlings.
If the plant has seedheads, place it in a bag rather than leaving it on the lawn. Do not compost seed-bearing weeds unless your compost system is designed to kill weed seeds. For a large area, first confirm the weed and turf, then compare hand removal, cultural fixes, and label-approved herbicides.
Step 2: Use herbicides only by the label
A preemergent herbicide is intended to stop certain seeds from establishing. Use one only when its label matches the identified weed, lawn type, application timing, and site. “Watergrass” alone is not enough to confirm that a product will work.
Postemergent herbicides act on weeds that are already growing. Control is generally most effective when target weeds are young and actively growing, but the right product, rate, weather limits, and retreatment interval depend on the label. Do not increase a rate or repeat an application sooner than directed to force faster results.
Before treatment, read the full label and wear the listed protective gear. Keep people and pets away as directed. Protect desirable plants and water features, and follow the label’s weather limits. If the product is not labeled for your turf species or the identified weed, do not use it.
Step 3: Apply carefully and check results
For a labeled treatment, measure the area and product as directed. Avoid spraying on a windy day or outside the label’s stated conditions. Do not assume that a brown or yellow plant is fully controlled; follow the product directions for judging results and any repeat application.
For hand removal, inspect the area again after pulling. For either method, watch for new seedlings and bare soil. Removing visible plants can leave space for more weeds if the lawn stays thin.
Diagnostic scenarios: what the clues may mean
These examples are practical scenarios, not claims about a particular lawn. They show why identification should come before treatment.
- A few broad-leaved plants with reddish, flattened bases: Barnyardgrass is one possibility. I would check the leaf collar and look for a branched seedhead before choosing a control.
- A coarse patch with a visible membranous ligule: Crabgrass may be more likely than barnyardgrass. I would confirm the species and check whether any product label covers it and the lawn type.
- Upright plants with a triangular stem: A sedge is a stronger possibility. I would not use a grass-weed treatment without confirming that it controls the identified sedge.
Maintain Turf and Equipment After Treatment
Follow-up means checking whether the weed is gone and helping the lawn fill open spots. It does not mean mowing very low or adding extra herbicide. Keep mowing, watering, and feeding in line with the needs of your turf species and any product label instructions.
Mow at the right height
Avoid scalping, which means cutting the lawn much shorter than its recommended height. Low mowing can thin turf and expose soil, giving weed seedlings room to establish. Set the mower for the lawn grass, and avoid changing the height just to cut down watergrass.
If the weed has mature seedheads, avoid spreading them with mowing. Bagging may help contain seed-bearing material, but use the mower maker’s instructions for its bag and discharge setup. Never remove guards or use equipment in a way the manufacturer does not allow.
Clean up and assess the patch
Dispose of pulled, seed-bearing plants as local rules allow. Clean the mower or hand tools as the manufacturer directs, especially if soil or plant material is stuck to them. This is good general cleanup; it does not replace correct weed identification or control.
Check treated areas at the interval given on the product label. Note whether plants are growing, fading, or producing seedheads. If the weed remains healthy, do not immediately apply more product. Recheck the identification and label directions first.
| Lawn situation | Sensible next step | Avoid |
|---|---|---|
| One or a few confirmed plants | Pull crown and roots in moist soil; bag seed-bearing plants | Leaving seedheads on the lawn |
| Many plants, ID confirmed | Consider a product labeled for that weed and turf | Using a product based only on “watergrass” |
| Weed may be a sedge | Confirm the ID and use a sedge-labeled option if needed | Assuming a grass-selective product will work |
| Lawn has bare patches | Restore dense turf using care suited to the grass type | Scalping or applying extra herbicide |
Prevent Recurrence and Store Products Safely
Prevention focuses on a dense, healthy lawn and careful use of products. Watergrass may return if plants set seed or the lawn has open soil. Good mowing and suitable irrigation and fertility can support turf, but they do not replace correct control when weeds are established.
Reduce the conditions that favor new weeds
Maintain the height recommended for your lawn species. Water and fertilize according to local guidance and the needs of your turf, rather than applying more than recommended. Repair bare areas with a method and timing suitable for your grass type.
If using a preemergent product, follow its label for target weeds, timing, site, and any limits on seeding or other lawn work. Timing is product- and region-specific; a calendar date from another location may not apply to your yard.
Store and dispose of products by label
Keep herbicides in their original containers with labels intact, stored as the label directs and away from children, pets, and food. Do not pour leftover mixture into a drain, onto the ground, or into a water feature. Follow label directions and local rules for leftover product and empty containers.
If you are unsure about the weed, lawn species, or product, pause and ask a local extension service or qualified turf professional. A short ID check is safer than treating the wrong plant.
Frequently Asked Questions
These short answers cover common questions about the name, identification, and control of watergrass. Because the term varies by region, treat it as a starting clue, not a confirmed diagnosis. Check plant features and product labels before taking action.
Is watergrass the same as barnyardgrass?
Not always. In many areas, “watergrass” refers to barnyardgrass, but the common name can describe other weeds in local use. Confirm the plant’s features before selecting a treatment.
What does barnyardgrass look like in a lawn?
It is a warm-season annual grass with broad leaves, a flattened or sometimes reddish stem base, and an open, branched seedhead when mature. It typically lacks a visible membranous ligule.
How can I tell watergrass from crabgrass?
Check the leaf collar and other features. Crabgrass usually has a membranous ligule and may have hairs on its leaves or sheaths. Growth stage can make identification harder, so compare several plants.
How can I tell if it is a sedge?
Yellow nutsedge has a triangular stem in cross-section and leaves arranged in three ranks. If you see those traits, do not assume it is a grassy weed.
Can I pull watergrass by hand?
Yes, hand-pulling can work for isolated plants. Pull when the soil is moist so you can remove the crown and roots. Bag plants with seedheads.
Will a grass-selective herbicide kill nutsedge?
Generally, grass-selective herbicides do not control sedges. Confirm the plant and use only a product labeled for the identified weed and your turf species.
When should I treat watergrass?
A preemergent product is appropriate only when its label timing and target-weed directions match your situation. Postemergent control generally works best on young, actively growing weeds, subject to label directions.
Can I mow watergrass out of the lawn?
Mowing alone is not a dependable way to remove an identified weed. Keep the mower at the height recommended for your turf, and avoid spreading mature seedheads.
What should I do if I cannot identify the plant?
Do not spray yet. Take photos of the whole plant, stem base, leaf collar, and seedhead if present. Ask a local extension service or qualified turf professional to confirm it.
Can the wrong herbicide damage my lawn?
Yes. A product not labeled for your turf species can injure desirable grass, and a product aimed at a different weed may fail to control the plant. Follow the full label.
(This article was written by one of our staff writers, Evan Bradley. Visit our Meet the Team page.)
