Canada Thistle (Cirsium arvense): Identification & Selective Herbicide Matrix
Quick Agronomic Summary
Triclopyr + Clopyralid or SpeedZone (2,4-D + Dicamba) kills Canada Thistle down to the horizontal roots.
- Diagnostic Marker 1: Erect stems with deeply lobed, crinkled leaves tipped with sharp, stiff spines
- Diagnostic Marker 2: Clusters of purple-lavender disc flowers lacking spiny involucres around the heads
- Diagnostic Marker 3: Aggressive, deep creeping horizontal root system giving rise to circular patches of shoots
What selective herbicide kills Canada Thistle in lawns?
Triclopyr + Clopyralid or SpeedZone (2,4-D + Dicamba) kills Canada Thistle down to the horizontal roots.
Canada thistle roots extend over 10 feet horizontally. Systemic auxin herbicides translocate throughout the root system to prevent resprouting.
When to spray Canada Thistle?
The ideal time is early fall when rosettes move sugars to roots, or early summer during the flower bud stage.
Never pull Canada thistle manually; root fragments break off and multiply the stand.
EPA-Registered Herbicides Labeled for Canada Thistle
The table below compares all selective herbicides in our database that control Canada Thistle, including active ingredient groups, application temperature limits (°F), and surfactant requirements.
| Brand Name & EPA Reg. | Active Ingredient & WSSA Group | Temp Window (°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 |
| TZone SE EPA Reg. 2217-920 |
Triclopyr 7.72%, 2,4-D 29.36%, Dicamba 2.22%, Sulfentrazone 0.66% Group 4 + Group 14 (Pyridine Auxin + Phenoxy + PPO Inhibitor) |
50°F – 80°F Rainfast: 3h |
Do NOT mix with surfactant when temperatures exceed 75°F. In cool spring or fall conditions (55°F–70°F), 0.5 tsp NIS per gallon improves waxy leaf penetration on Wild Violet. | Check Price at DoMyOwn View on Amazon |
Turfgrass Compatibility Matrix for Canada Thistle Herbicides
Always verify that your chosen herbicide is safe for your specific lawn grass before broadcast spraying:
How to Distinguish Canada Thistle from Lookalike Weeds
| Lookalike Species | Key Botanical & Diagnostic Difference |
|---|---|
| Dandelion | Young thistle leaves have sharp, stiff spines along the leaf margins; dandelion leaves have toothed edges with zero spines. |