For River Parishes lawns, the best weed control is a spring and fall pre-emergent program paired with early spot treatment and a thick lawn mowed at the right height. Apply summer pre-emergent in late February to early March, fall pre-emergent in late September, and use nutsedge-specific herbicides like Sedgehammer on active nutsedge instead of pulling it.
Weeds are usually a symptom, not the root problem. If the lawn is thin, underfed, overwatered, or scalped, weeds rush in. The right plan — combining pre-emergent barriers, precise post-emergent timing, and good cultural practices — stops them before they dominate the yard. South Louisiana's long growing season means more weed cycles per year than most regions, so staying ahead of the calendar is everything.
This guide covers identification of the weeds most common to the River Parishes, pre-emergent and post-emergent strategies, organic alternatives, and a month-by-month calendar so you always know what to apply and when.
Louisiana Weed Identification Guide
Before you treat, know what you are dealing with. Broadleaf weeds, grassy weeds, and sedges each respond to different chemistry. Using the wrong product wastes money and stresses the turf. Refer to the tables below to identify the most common Louisiana lawn weeds.
Common Broadleaf Weeds
Broadleaf weeds have wide, net-veined leaves and often produce showy flowers. In the River Parishes these are the most visible (and most frustrating) weeds homeowners face. Most respond well to selective 2,4-D / dicamba / MCPP blends applied post-emergent.
| Weed | Appearance | Season | Control |
|---|---|---|---|
| Broadleaf Dollarweed | Round, penny-sized leaves with scalloped edges; white flowers; likes wet soil | Spring through fall | Improve drainage; selective broadleaf herbicide; reduces when watering cuts back |
| Broadleaf Clover (White / Dutch) | Three-leaf clusters, small white or pink flowers; low-growing; spreads fast | Year-round in Louisiana | Broadleaf herbicide with dicamba; improve nitrogen levels (clover thrives in low-N soil) |
| Broadleaf Henbit | Square stems, scalloped opposite leaves, purple-pink tubular flowers | Winter annual (emerges fall, flowers spring) | Pre-emergent in early fall; post-emergent broadleaf spray in late winter |
| Broadleaf Chickweed | Small oval leaves, slender stems, tiny white star-shaped flowers; forms dense mats | Winter annual | Pre-emergent (September); post-emergent broadleaf herbicide; hand-pull small patches |
Grassy Weeds
Grassy weeds resemble desirable lawn grasses but grow faster and coarser. They blend into the turf until they outgrow it and become visible as clumps. Grassy weeds require different chemistry than broadleaf herbicides — standard weed-and-feed products will not touch them.
| Weed | Appearance | Season | Control |
|---|---|---|---|
| Grassy Crabgrass | Light green, coarse-textured blades; low-growing with radiating stems; seed head resembles crab legs | Summer annual | Pre-emergent when soil hits 55°F (late Feb-early Mar); post-emergent quinclorac or MSMA in St. Augustine |
| Grassy Goosegrass | Darker green than crabgrass; flattened stems; white-center seed heads; grows in compacted soil | Summer annual | Pre-emergent (same timing as crabgrass); reduce compaction; post-emergent Revolver or MSMA |
| Grassy Dallisgrass | Coarse, thick clumps with prominent midrib; black seed heads; wiry root system | Perennial | Difficult to control; spot-treat with glyphosate (non-selective) or MSMA; dig out deep roots |
Sedges (Nutgrass / Nutsedge)
Sedges look like grass but are a completely different plant family. They have triangular stems (roll a stem between your fingers — you will feel the edges) and grow faster than lawn grass, often appearing the day after mowing. Standard grassy weed herbicides will not kill sedges. They require dedicated sedge-specific chemistry.
| Weed | Appearance | Season | Control |
|---|---|---|---|
| Sedge Yellow Nutsedge | Light yellow-green, glossy leaves; triangular stems; yellow-brown seed heads; tubers (nutlets) on roots | Spring through fall | Sedgehammer (halosulfuron) when 3-4 inches tall; repeat every 4-6 weeks; do not pull (spreads tubers) |
| Sedge Purple Nutsedge | Darker green, smaller leaves; purple seed heads; aggressive tuber chain; harder to control than yellow | Spring through fall | Sedgehammer + surfactant; may need repeat applications; improve drainage |
Pre-emergent Timing for the River Parishes
Pre-emergent herbicides create a chemical barrier in the top layer of soil that kills weed seeds as they germinate. They do not kill existing weeds — you must apply before the seeds sprout. Timing is everything, and in South Louisiana the window is narrower than up north because our soil warms up faster.
The key trigger is soil temperature at 55°F at a depth of 2-4 inches. For the River Parishes (St. John the Baptist, St. Charles, Ascension parishes), that happens:
- Summer weeds (crabgrass, goosegrass): Apply pre-emergent late February to early March, when forsythia and redbud trees begin blooming. Soil reaches 55°F consistently in this window. A second "split" application 6-8 weeks later extends coverage through the long Louisiana growing season.
- Winter weeds (henbit, chickweed, annual bluegrass): Apply pre-emergent in late September, when soil temps drop back through 70°F toward 55°F. This stops winter annuals before they establish.
Pre-emergent Pitfall
Do NOT apply pre-emergent if you are seeding or laying sod this spring — the barrier prevents ALL seeds from germinating, including your new grass. Wait until the new turf is fully established (after 3-4 mowings) before starting a pre-emergent program.
For best results, water in the pre-emergent with 1/2 inch of irrigation within 24 hours of application. Do not aerate or dethatch for at least 4 weeks after applying, or you will break the chemical barrier and let weeds through.
Post-emergent Treatment: Selective vs. Non-selective
When weeds are already visible, you need post-emergent herbicides. These fall into two categories:
- Selective herbicides target specific weed families (broadleaf or grassy) while leaving your lawn grass unharmed. Examples: 2,4-D / dicamba / MCPP blends for broadleaf weeds; quinclorac for crabgrass; sethoxydim for grassy weeds in broadleaf turf.
- Non-selective herbicides (glyphosate, glufosinate) kill every green plant they touch. Use ONLY for spot treatment of perennial weeds like dallisgrass or for clearing an area before renovation.
Spot Treatment Best Practices
- Use a small pump sprayer or ready-to-use trigger bottle — never broadcast a non-selective product over the whole lawn.
- Add a non-ionic surfactant (1-2 drops per quart) to help the herbicide stick to waxy leaves.
- Treat when temperatures are between 60-85°F and no rain is forecast for 24 hours.
- Do not mow for 2-3 days before or after treatment to give the herbicide time to translocate to the roots.
- Repeat applications 2-3 weeks apart for stubborn perennial weeds.
Cultural Control: Crowd Out Weeds with a Thicker Lawn
The most effective long-term weed strategy is a lawn so thick and healthy that weed seeds cannot find bare soil to germinate in. This is called cultural control, and it beats spraying every time. Three factors matter most:
Proper Mowing Height
Mowing too low is the #1 cause of weed invasions in the River Parishes. Scalped grass lets sunlight hit the soil, which triggers weed seed germination. Each grass type has a recommended height range:
- St. Augustine: 3-4 inches — never cut more than 1/3 of the blade at once. See our full mowing height guide for details.
- Bermuda: 1-2 inches.
- Zoysia: 1.5-2.5 inches.
- Centipede: 1.5-2 inches.
Taller grass shades the soil, keeps it cooler, and leaves no room for weed seedlings. It also develops deeper roots, making the lawn more drought-tolerant.
Watering Depth
Shallow, frequent watering grows shallow grass roots and creates a perfect environment for dollarweed and sedges. Water deeply and infrequently: 1 inch per week (including rainfall) in a single watering or two split applications. Water early in the morning so the turf dries before evening, reducing disease pressure.
Fertilization
A properly fed lawn outcompetes weeds naturally. Follow a seasonal fertilizing plan suited to your grass type. Key rules:
- Test your soil pH first — Louisiana soils are often acidic; lime may be needed to reach the 6.0-6.5 range.
- Use slow-release nitrogen: 1 lb of N per 1,000 sq ft per growing month (April-September for warm-season grasses).
- Do not over-fertilize in spring or fall — excess nitrogen feeds weeds as much as grass.
- Iron supplements (chelated iron) green up the lawn without pushing excessive growth that weeds exploit.
Organic Weed Control Options
Not every homeowner wants synthetic herbicides. Several organic approaches can keep weed pressure manageable, especially when combined with good cultural practices.
Corn Gluten Meal (Pre-emergent)
Corn gluten meal is a natural pre-emergent that inhibits root development in germinating weed seeds. Apply at 20 lbs per 1,000 sq ft in late February (same timing as synthetic pre-emergents) and again in late September for winter weeds. It also provides about 10% nitrogen, giving the lawn a gentle feeding. Be aware: it is less effective than synthetic pre-emergents on heavy weed pressure, and it must stay dry for 3-5 days after application to form the barrier.
Vinegar-based Herbicides
Household vinegar (5% acetic acid) is a weak contact killer — it burns the foliage of small annual weeds but rarely kills the roots. Horticultural vinegar (20-30% acetic acid) is more effective but is non-selective and can burn skin. Best use: spot-spray young broadleaf seedlings in sidewalk cracks or bed edges on a sunny day. Reapply every 5-7 days. These products have no soil activity, so they are safe around vegetable gardens.
Hand Pulling
For small infestations, nothing beats old-fashioned hand pulling. The best time to pull is after a rain when the soil is soft. Use a weeding tool (dandelion digger or fishtail weeder) to get the entire root system. For nutsedge, never pull — you break the tubers off underground and multiply the infestation. Dig nutsedge out with a trowel, removing at least 4 inches of soil around the base.
Organic Program Summary
Corn gluten meal in February & September + vinegar spot-spray as needed + hand pulling after rain + 3.5-4 inch mowing height = a surprisingly effective organic program for low-to-moderate weed pressure. For heavy infestations, start with targeted synthetic products to knock it down, then maintain organically.
Nutsedge: Why It Is Different and How to Beat It
Nutsedge (often called nutgrass) deserves its own section because it is the most misidentified and mistreated weed in Louisiana. It is not a grass — it is a sedge — and the standard lawn herbicides homeowners buy at the big-box store will not touch it.
What Makes Nutsedge Unique
- Triangular stem. Roll a stem between your fingers. If you feel edges, it is a sedge, not grass.
- Tubers (nutlets). Nutsedge spreads through underground tubers that can stay dormant for years. Pulling the top breaks the tubers loose, and each piece grows a new plant. This is why pulling makes it worse.
- Fast growth. Nutsedge can grow 2 inches in 24 hours after mowing. It outruns the lawn and sticks up above the canopy.
- Wet-soil indicator. Nutsedge thrives in poorly drained, wet areas. If you have nutsedge, you likely have a drainage or overwatering issue.
Sedgehammer Application Timing
The most effective product for home lawns is Sedgehammer (halosulfuron-methyl). It is selective — it kills sedges without harming your lawn grass. Follow this protocol:
- Apply when nutsedge is 3-4 inches tall and actively growing (soil temp above 60°F). In the River Parishes, the first application window is mid-April through May.
- Add a non-ionic surfactant at 0.25% (1 teaspoon per gallon of spray mix) to penetrate the waxy sedge leaf.
- Spray thoroughly but not to runoff. A single application kills existing plants but may not stop the tubers.
- Repeat every 4-6 weeks through the growing season — typically 3-4 applications total. Each round exhausts more tubers.
- Do not mow for 3 days before or after application so the herbicide translocates to the tuber system.
Bermuda Grass Caution
Sedgehammer is safe for most warm-season grasses (St. Augustine, Bermuda, Zoysia, Centipede) at labeled rates. Do not exceed the labeled rate on Bermuda or Centipede — these are more sensitive. Always read and follow the label.
Post-emergent Calendar: What to Use Each Month
Here is a month-by-month guide for active weed control in the River Parishes. Adjust for your specific grass type and the weather each year.
January - February
Weeds active: Henbit, chickweed, annual bluegrass (winter annuals). Action: Spot-treat with selective broadleaf herbicide (2,4-D / dicamba) on days above 50°F. Do not apply pre-emergent — it is too late for winter weeds, too early for summer. Hand-pull if infestations are small.
March
Action: Apply pre-emergent NOW (late Feb-early Mar). Soil temperatures cross 55°F this month. Use prodiamine or dithiopyr for crabgrass and goosegrass. If you missed pre-emergent, use dithiopyr which has some early post-emergent activity on tiny crabgrass seedlings.
April
Weeds active: Crabgrass seedlings emerging, dollarweed, clover. Action: Spot-treat broadleaf weeds with selective herbicide. Apply first round of Sedgehammer if nutsedge is 3-4 inches tall. Split pre-emergent application (6 weeks after first) if you used prodiamine.
May
Weeds active: Full summer weed flush — crabgrass, goosegrass, nutsedge, dollarweed. Action: Second Sedgehammer application. Spot-treat crabgrass patches with quinclorac. Continue broadleaf spot treatment. Apply post-emergent before weeds exceed 4 inches for best results.
June - July
Weeds active: Peak weed season. Action: Third Sedgehammer application (if needed). Spot-treat as weeds appear. Avoid spraying in heat above 90°F — herbicide can volatilize and drift, or burn the lawn. Focus on maintaining proper mowing height at 3.5-4 inches to shade out weeds.
August
Weeds active: Late summer flush of crabgrass and goosegrass. Action: Last call for Sedgehammer if nutsedge is still active. Plan for winter weed pre-emergent — mark your calendar for late September. Do not fertilize yet; wait until the heat breaks.
September - October
Action: Apply pre-emergent for winter weeds (henbit, chickweed, annual bluegrass) in late September. Follow fall fertilizing guidelines. Spot-treat any remaining summer broadleaf weeds before they go to seed. This is a good time to core-aerate (after pre-emergent has been down for 4+ weeks, or before applying it).
November - December
Weeds active: Winter annuals emerging. Action: Spot-treat winter broadleaf weeds with 2,4-D / dicamba on mild days. Mulch fallen leaves instead of bagging — returning organic matter feeds the soil. Do heavy cleanup of bed edges and fence lines where weeds re-seed first.
Building a Complete Weed Management Plan
A successful weed control program in the River Parishes layers all the strategies above into a year-round system:
- Know your grass type. Different grasses tolerate different herbicides. Identify yours with our grass type guide.
- Pre-emergent in spring and fall. Late February and late September — never skip these two applications.
- Mow at the right height. 3.5-4 inches for St. Augustine crowds out more weeds than any chemical can. Read our mowing height guide.
- Fertilize on schedule. A seasonal fertilizing plan keeps the lawn dense and competitive against weeds.
- Spot-treat early. Do not wait until weeds have gone to seed. A 2-second spray on a single weed today prevents 5,000 seeds next season.
- Water correctly. Deep, infrequent watering (1 inch per week) discourages dollarweed and nutsedge.
- Monitor bed edges and fence lines. Weeds always start at the margin and move inward. Pre-emergent granules on these borders in spring and fall stop the invasion before it crosses into the turf.
Also check our pest and disease guide for issues like chinch bugs and brown patch that weaken the turf and invite weeds. A healthy lawn resists both pests and weeds.
When to Call a Professional
If you are making 3+ herbicide applications per season and the weed pressure is not declining, or if you have large areas overtaken by nutsedge, dallisgrass, or perennial weeds, it is time for professional help. Professional applicators have access to products (like Certainty, Monument, and Celsius) that are not available to homeowners, and they can calibrate rates precisely for your grass type.
Stop fighting weeds — get a professional weed control program from Xcellent1 Lawn Care.
Our crew services the River Parishes with custom weed management plans tailored to your grass type, property size, and weed pressure. We use commercial-grade products and calibrated application schedules so you get results without the guesswork.
Frequently Asked Questions
When should I apply pre-emergent in Louisiana?
Apply summer pre-emergent in late February to early March, when soil temperatures are reaching 55°F and crabgrass is about to sprout. Apply winter pre-emergent again in late September before henbit and chickweed germinate. In the River Parishes, those two applications are the backbone of weed prevention.
How do I kill nutsedge?
Use a sedge-specific herbicide such as Sedgehammer when the nutsedge is 3 to 4 inches tall and actively growing. Add a surfactant, repeat every 4 to 6 weeks, and do not pull it because pulling breaks off tubers and spreads the infestation. Poor drainage and overwatering also need to be fixed or it will keep coming back.
Does pre-emergent kill existing weeds?
No. Pre-emergent herbicides stop weed seeds from germinating, but they do not kill weeds that are already visible. If weeds are up, use the right post-emergent product instead and save pre-emergent for the next germination window.
What weeds can I spray in St. Augustine without hurting the grass?
Broadleaf weeds such as clover, henbit, and dollarweed can usually be treated with a selective broadleaf herbicide labeled for St. Augustine. Crabgrass needs a grassy-weed product, and nutsedge needs a sedge-specific product, so matching the herbicide to the weed is critical. Always spray on a mild day and follow the label for your turf.
Why do weeds keep coming back after I spray them?
Weeds usually return because the lawn is thin, cut too short, overwatered, or underfed, which leaves bare soil for new seeds to fill. A thick lawn mowed at the right height, watered deeply, and fertilized on schedule will crowd out many weeds before they start. In the River Parishes, cultural control is just as important as herbicide timing.