Crabgrass Control in Missouri Lawns: Identification, Prevention, and Removal

Bottom line up front: Crabgrass is the most common lawn weed in St. Charles County, and the best time to stop it is in early spring before soil temperatures hit 55°F. If you’re seeing crabgrass now, you need post-emergent treatment — and you need to act before it drops seeds.

What Is Crabgrass?

Crabgrass (Digitaria sanguinalis and Digitaria ischaemum) is a warm-season annual grass weed that germinates in spring, grows aggressively through summer, produces thousands of seeds per plant, and dies with the first hard frost. It earned its name from the sprawling, crab-like growth pattern where stems radiate outward from a central point and root at the nodes.

In Missouri’s transition zone climate, crabgrass thrives in the hot, humid summers that are typical for Wentzville, O’Fallon, St. Peters, and throughout St. Charles County.

According to the University of Missouri Extension, crabgrass is the most economically damaging lawn weed in the state, responsible for more lawn renovation requests than any other single pest.

How to Identify Crabgrass

Quick ID: Crabgrass looks different at every stage. Grab the free Missouri Weed ID Cheat Sheet for printable photos and side-by-side comparisons of all 16 common lawn weeds.

Crabgrass looks different at each growth stage:

Seedling stage (April-May): Light green, wider than desirable turfgrass blades, grows flat against the soil. Often confused with tall fescue clumps, but crabgrass blades are lighter in color and have a more papery texture.

Mature stage (June-August): Sprawling clumps 6-18 inches across. Stems are flattened (not round like most turfgrasses) and radiate from a central crown. Leaf blades are 1/4 to 1/2 inch wide with a distinct mid-vein. The ligule (where blade meets sheath) is tall and membranous — this is the key identifier that separates crabgrass from lookalikes like goosegrass.

Seed head stage (August-September): Finger-like seed heads on stalks rising above the leaf blades. Each plant produces 150,000+ seeds that can remain viable in soil for 3+ years.

Common lookalikes in Missouri: Tall fescue clumps (darker green, round stems), goosegrass (silver-white center, flat stems like crabgrass), and quackgrass (perennial with rhizomes, not annual).

Why Crabgrass Is a Problem

• Competition: Crabgrass outcompetes desirable turf for water, nutrients, and sunlight. A single plant can spread to cover 2+ square feet.
• Appearance: Its coarse texture and lighter green color stand out against fine turf, creating patchy, uneven lawns.
• Seasonal die-off: When crabgrass dies with the first frost, it leaves bare patches that invite erosion and spring weed invasion.
• Seed bank: Every plant you let go to seed this year guarantees 100+ new plants next year.

Prevention: The Pre-Emergent Strategy

The single most effective crabgrass control method is prevention. In St. Charles County, timing is everything.

When to Apply Pre-Emergent

Apply when soil temperature at 2-inch depth reaches 50-55°F for 3-5 consecutive days. In our area, this typically falls between March 15 and April 15, though it varies by year:

Year	Typical Window Opens	Notes
Average	April 1	Standard target date for Wentzville/O’Fallon
Early spring	March 15-20	Warm March with early soil warming
Late spring	April 10-15	Cold, wet March delaying soil warmup

Pro tip: Watch for forsythia blooming. The old gardener’s rule is 100% reliable: apply pre-emergent when forsythia bushes are in full yellow bloom.

Which Pre-Emergent to Use

Product Type	Active Ingredient	Duration	Best For
Prodiamine (Barricade)	Prodiamine	4-6 months	Long-lasting, one application
Dithiopyr (Dimension)	Dithiopyr	3-4 months	Has early post-emergent activity too
Pendimethalin (Pendulum)	Pendimethalin	3-4 months	Budget option, widely available
Corn gluten meal	Natural	4-6 weeks	Organic option, also feeds the lawn

For most St. Charles County lawns, prodiamine applied once in early April provides season-long control. Split applications (half in late March, half in late May) work even better for lawns with heavy crabgrass history.

Application Tips

1. Apply to a dry lawn, then water in with 1/2 inch of irrigation within 48 hours
2. Calibrate your spreader — over-application kills desirable grass roots; under-application leaves gaps in the chemical barrier
3. Do not aerate after applying — aeration breaks the chemical barrier. If you need to aerate, do it first, then apply pre-emergent
4. Skip if overseeding — pre-emergents prevent grass seed from germinating too. If you’re overseeding in spring, skip the pre-emergent in those areas

Removal: Killing Existing Crabgrass

If crabgrass is already growing in your lawn, prevention is no longer the answer. You need active removal.

Manual Removal (Small Infestations)

For a few plants, hand-pulling works surprisingly well. Crabgrass has a shallow, fibrous root system. Pull after rain or irrigation when soil is soft. Remove before seed heads appear (typically August). Bag and dispose — don’t compost seeding crabgrass.

Post-Emergent Herbicides

For larger infestations, selective herbicides are the answer:

Herbicide	Active Ingredient	When to Use	Notes
Quinclorac (Drive XLR8)	Quinclorac	Any growth stage	Safe on most cool-season turf; kills crabgrass in 7-14 days
MSMA/DSMA	Organic arsenicals	Mature plants only	Effective but restricted in many areas; not for residential use
Fenoxaprop (Acclaim Extra)	Fenoxaprop-p-ethyl	Young to mature	Works quickly; don’t apply in heat above 85°F

For Missouri lawns, quinclorac is the go-to choice. It’s effective at any growth stage, safe on tall fescue and Kentucky bluegrass, and widely available at local garden centers.

Apply when temperatures are between 60-85°F. Two applications 10-14 days apart often give better results than a single heavy application. Always add a surfactant (spreader-sticker) for better leaf coverage.

The Nuclear Option: Non-Selective Control

For lawns where crabgrass has taken over more than 50% of the area, consider a full renovation:

1. Spray the entire area with glyphosate in late summer (August)
2. Wait 7-10 days for complete kill
3. Mow dead vegetation as low as possible
4. Core aerate heavily (2-3 passes)
5. Overseed with tall fescue in early September
6. Apply starter fertilizer and keep moist for 3 weeks

This costs more upfront but gives you a clean slate. Many Wentzville homeowners with older lawns choose this approach after years of fighting crabgrass.

The Full-Season Crabgrass Control Calendar for St. Charles County

Month	Action	Notes
March	Soil temp monitoring	Start checking soil temps daily from March 10
Late March-April	Pre-emergent application	Apply when forsythia blooms
May	Scout for breakthrough	Hand-pull any crabgrass that slipped through
June-July	Post-emergent treatment	Apply quinclorac to any visible crabgrass
August	Prevent seed production	Critical month — kill or remove before seeds drop
September	Overseed bare patches	Fill in where crabgrass died
October	Fall fertilizer	Strengthen turf for next year’s competition

Common Mistakes St. Charles County Homeowners Make

1. Applying pre-emergent too late. If you wait until you see crabgrass, you’re 6 weeks too late. Pre-emergent must be in place BEFORE germination.
2. Skipping the second application. One application in April wears off by August. A split application gives better season-long protection.
3. Confusing crabgrass with tall fescue. Pulling tall fescue clumps by hand doesn’t solve the problem — you need a different approach for perennial grass weeds.
4. Not watering in pre-emergent. Dry pre-emergent on the soil surface does nothing. It must be watered into the soil within 48 hours.
5. Mowing too short. Crabgrass seeds need light to germinate. Taller turf (3-4 inches) shades the soil and reduces crabgrass germination by up to 60%.

When to Call a Professional

If you’ve tried the DIY approach and crabgrass keeps winning, it might be time to bring in help. A professional lawn care provider can:

• Apply commercial-grade pre-emergents with calibrated equipment
• Identify exactly which weeds you’re dealing with
• Create a full-season treatment plan customized to your soil and grass type
• Spot-treat problem areas throughout the season

Midwest Lawn Care connects St. Charles County homeowners with vetted local lawn care providers who know our soil, our climate, and our weeds. Request help with a provider today.

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Last updated: May 18, 2026. Reviewed for accuracy against current University of Missouri Extension recommendations.