Canada Thistle
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Canada Thistle is a persistent, invasive weed that spreads through both wind-blown seeds and underground roots (rhizomes). It forms dense colonies that outcompete crops, pastures, and native plants, making it one of the most problematic noxious weeds in North America. It forms dense patches that choke out desirable grasses and crops. It is difficult to eradicate, roots can grow 10+ feed deep and 15 feet outward per year. Seeds can remain viable in soil for 20+ years. Livestock avoid it due to spines, reducing grazing value.
Herbicides for Noxious Weeds
| Herbicide Name | Active Ingredient(s) | Notes / Timing |
|---|---|---|
| Milestone® | Aminopyralid | Apply at rosette to early bud stage. Strong residual control on thistles. |
| Chaparral® | Aminopyralid + Metsulfuron | Apply spring or fall to actively growing plants. Controls thistle & other broadleaf weeds. |
| GrazonNext® HL | Aminopyralid + 2,4-D | Best on actively growing plants in spring. Provides residual suppression. |
| Curtail® / Stinger® | Clopyralid (± 2,4-D) | Effective on Canada thistle in pasture & non-cropland. Use at rosette to bolting stage. |
| Tordon® 22K (Restricted Use) | Picloram | Apply spring or fall. Long-lasting soil residual. Groundwater restrictions apply. |
| Dicamba (e.g., Banvel / Clarity) | Dicamba | Apply at early growth stage. Often tank mixed with 2,4-D. Drift precautions needed. |
| 2,4-D (Amine or Ester) | 2,4-D | Works best on young rosettes. Not effective alone on established perennial patches. |
| Telar® / Escort® XP | Chlorsulfuron / Metsulfuron | ALS inhibitor. Rotate with other modes of action to prevent resistance. |
| Glyphosate (e.g., Roundup) | Glyphosate | Non-selective. Use for spot spraying or pre-plant treatments. Expect regrowth if roots remain. |