Asteraceae or Sunflower Family
Growth Habit: Perennial, grows up to 4 feet tall.
Leaves: Deeply toothed with spines, hairy on underside, varies quite a lot from plant to plant.
Stems: Smooth to slightly hairy, branched at top.
Flowers: Small bristly cluster, 3/8 to 5/8 inches in diameter, light lavender to deep rose purple, male or females.
Roots: Extensive creeping horizontal roots up to 16 feet long and 2 to 22 feet deep.
Seeds: Produces 9,300 seeds per plant, viable up to 22 years.
Reproduction: Vegetatively from horizontal creeping roots or from seeds.
Habitat: Found in meadows, roadsides, native grasslands, pastures, and waste places.
Handpulling: Only effective on small infestations if done consistently and persistently throughout the growing season and for multiple years. Be sure to wear gloves.
Mowing: Mowing is an inconsistent method of control for Canada thistle, depending on the conditions present at the site. In some instances, mowing two to three times annually for a period of three or more years can eliminate an infestation. In other situations the same regime will only accomplish a reduced seed crop.
Biological Control: N/A
Grazing: Not recommended because livestock tend to avoid it because of its spiny stems and leaves.
Herbicide: The following herbicides are labelled for control of Canada thistle. Always consult product labels and read them carefully to ensure correct species/land management usage and chemical application.
|Trade Name:||Active Ingredient:||Rate:||Efficacy:||Comments:|
|Tordon 22k||picloram||1 qt/acre||most effective on actively growing plants; spring or fall||Cannot use near surface water, shallow water, landscaped areas and current or future vegetable gardens (Restricted Herbicide - need an applicator license to use.)|
|Milestone||aminopyralid||5-7 oz/acre||most effective in actively growing plants; spring or fall||Can be applied to waters edge; cannot be used in landscaped areas and current or future vegetable gardens, mulch or manure from treated areas should not be applied to vegetable gardens or composted for vegetable gardens|
|Forefront||aminopyralid + 2,4-D||2-2.5 pts/acre||most effective in actively growing plants; spring or fall||Can be applied to waters edge; cannot be used in landscaped areas and current or future vegetable gardens, mulch or manure from treated areas should not be applied to vegetable gardens or composted for vegetable gardens|
|Curtail||clopyralid + 2,4-D||2-4 qts/acre||most effective in rosette to bud stage||Do not apply to shallow groundwater areas|
|Transline||clopyralid||1-1.3 pts/acre||least effective herbicide listed||Do not apply to shallow groundwater areas|