How to Kill Prostrate Knotweed in Tall Fescue Without Hurting Your Lawn
Direct Agronomic Answer
To selectively kill Prostrate Knotweed in Tall Fescue without damaging your turf, apply SpeedZone Lawn Weed Killer (2,4-D 28.57%, Mecoprop-p 5.88%, Dicamba 1.71%, Carfentrazone-ethyl 0.62%), Barricade 4FL (Prodiamine 65 WDG) (Prodiamine 40.7% (or 65% WDG)) when air temperatures are between 50°F and 85°F.
Once Knotweed stems mature and turn wiry in summer, they become highly resistant to post-emergents. Pre-emergent Prodiamine applied in early spring prevents emergence.
1. Labeled Safe Herbicides That Kill Prostrate Knotweed in Tall Fescue
| Recommended Product | Active Ingredient & Group | Application Temp (°F) | Surfactant & Mixing Protocol | Where to Buy |
|---|---|---|---|---|
| SpeedZone Lawn Weed Killer EPA Reg. 2217-833 |
2,4-D 28.57%, Mecoprop-p 5.88%, Dicamba 1.71%, Carfentrazone-ethyl 0.62% Group 4 + Group 14 (Synthetic Auxins + PPO Inhibitor) |
50°F – 85°F Rainfast: 3h |
Do NOT add surfactant. Adding NIS or MSO increases ester volatility and causes severe contact burn on desirable cool-season turf. | 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 |
3. Optimal Seasonal Timing & Temperature Thresholds
Apply post-emergents in early spring when seedlings first emerge along compacted sidewalk edges.
Core aerating compacted soil eliminates the environmental niche knotweed exploits.
4. Diagnostic Checklist: Confirm It Is Prostrate Knotweed Before Spraying
- Wiry, prostrate stems forming tough circular mats in heavily trampled, compacted turf
- Small, dull blue-green oblong leaves with papery sheaths (ochrea) at each swollen stem joint
- Inconspicuous tiny pinkish-white flowers clustered in leaf axils
Not 100% sure? Use our AI Photo Weed Scanner or review the full Prostrate Knotweed Botanical Profile.