How to Kill Smooth & Large Crabgrass in Kentucky Bluegrass Without Hurting Your Lawn
Direct Agronomic Answer
To selectively kill Smooth & Large Crabgrass in Kentucky Bluegrass without damaging your turf, apply Tenacity (Mesotrione 40%), Drive XLR8 (Quinclorac 18.92%) when air temperatures are between 55°F and 85°F.
For early 1–3 leaf stages and mature 2–4 tiller plants, Quinclorac paired with a methylated seed oil (MSO) surfactant provides rapid systemic control within 7 to 14 days. In St. Augustine and Centipede lawns where Quinclorac causes severe chlorosis, Atrazine or Mesotrione (for Centipede only) must be used instead.
1. Labeled Safe Herbicides That Kill Smooth & Large Crabgrass in Kentucky Bluegrass
| Recommended Product | Active Ingredient & Group | Application Temp (°F) | Surfactant & Mixing Protocol | Where to Buy |
|---|---|---|---|---|
| Tenacity EPA Reg. 100-1267 |
Mesotrione 40% Group 27 (HPPD Inhibitor) |
55°F – 85°F Rainfast: 6h |
Always apply with Non-Ionic Surfactant (NIS) at 1 tsp (5 mL) per gallon of water for post-emergent applications. Causes temporary white bleaching on susceptible weeds and turf tips. | Check Price at DoMyOwn View on Amazon |
| Drive XLR8 EPA Reg. 7969-272 |
Quinclorac 18.92% Group 4 (Synthetic Auxin / Quinoline Carboxylic Acid) |
60°F – 85°F Rainfast: 1h |
Requires Methylated Seed Oil (MSO) surfactant at 1.5 tbsp (0.75 fl oz) per gallon of water for effective cuticle penetration on multi-tiller crabgrass. | Check Price at DoMyOwn View on Amazon |
| Acclaim Extra EPA Reg. 432-950 |
Fenoxaprop-p-ethyl 6.59% Group 1 (ACCase Inhibitor) |
60°F – 85°F Rainfast: 1h |
Add Non-Ionic Surfactant (NIS) at 0.5 tsp per gallon only when targeting mature multi-tiller Goosegrass or Japanese Stiltgrass. Never tank-mix with 2,4-D (causes antagonism). | Check Price at DoMyOwn View on Amazon |
| Pylex Herbicide EPA Reg. 7969-327 |
Topramezone 29.7% Group 27 (HPPD Inhibitor / Pyrazolone) |
55°F – 85°F Rainfast: 1h |
Must be applied with Methylated Seed Oil (MSO) at 1 to 1.5 tsp per gallon of water. Tank-mixing with Triclopyr Ester reduces white bleaching and speeds up Bermudagrass and Goosegrass mortality. | Check Price at DoMyOwn View on Amazon |
| Barricade 4FL (Prodiamine 65 WDG) EPA Reg. 100-1139 |
Prodiamine 40.7% (or 65% WDG) Group 3 (Microtubule Assembly Inhibitor / Dinitroaniline) |
45°F – 90°F Rainfast: 0h |
Pre-emergent soil barrier: do NOT use foliar surfactant. Must be watered in with 0.5 inches of irrigation or rainfall within 14 days of application to activate. | Check Price at DoMyOwn View on Amazon |
2. What NOT to Spray on Kentucky Bluegrass When Treating Smooth & Large Crabgrass
Warning: Common Smooth & Large Crabgrass Killers That Damage Kentucky Bluegrass
Many retail herbicides advertised for Smooth & Large Crabgrass are formulated for different turf zones and will severely injure Kentucky Bluegrass:
- AVOID Hi-Yield Atrazine Weed Killer (Atrazine 40.8%): Rated 'avoid' on Kentucky Bluegrass — high risk of turf phytotoxicity or stunting.
3. Optimal Seasonal Timing & Temperature Thresholds
Apply pre-emergent Prodiamine or Dithiopyr when 4-inch soil temperatures reach 50°F–55°F for three consecutive days, and spray post-emergent herbicides in late spring when seedlings have 2 to 3 leaves.
Post-emergent applications are most effective when Crabgrass is actively growing in moist soil and air temperatures remain below 85°F. Spraying mature multi-tiller plants in late August during drought stress significantly reduces herbicide translocation.
4. Diagnostic Checklist: Confirm It Is Smooth & Large Crabgrass Before Spraying
- Light apple-green coarse blades growing in a prostrate star-like rosette
- Membranous, tall jagged ligule with sparse hairs at the collar region
- Finger-like seedheads (3 to 5 spikes) emerging in mid-to-late summer
Not 100% sure? Use our AI Photo Weed Scanner or review the full Smooth & Large Crabgrass Botanical Profile.