Canada Thistle is a very aggressive noxious weed. It is extremely hardy and difficult to get rid of, leading to many County residents having this invasive weed in their backyards and fields.

• Distinguishable by its purplish flowers and spiny green leaves.
• Leaves are arranged alternately, slightly clasping up along the stem of the plant. The leaves have a plastic feeling and are irregularly lobed with sharp spines.
• Stems are hollow and usually smooth, although there may be spines present near the base of the plant.
• Flowers range from white to purple, clustering to resemble a single flower.
• Mature plant height ranges from 30 to 180cm.
• A similar plant often mistaken for Canada Thistle is Bull Thistle. The easiest way to distinguish between these two plants is that Bull Thistle has much larger flower heads than Canada Thistle. It also has spines or prickles on the flowers and stems, whereas Canada Thistle does not.

• Almost everywhere in all soil types in Western Canada.
• This weed infests crops, pastures, rangelands, waste areas, roadsides, edges of sloughs and dug-outs, shelterbelts, and non-crop areas.
• Infestations typically start on disturbed ground, including ditch banks, overgrazed pastures, tilled fields or abandoned sites.

Canada Thistle is a creeping perennial which begins growth in the early spring. Flowering occurs primarily in early spring but may occur throughout the summer and fall.

Canada Thistle reproduces primarily by its intricate rooting system (rhizomes), which enable the plant to recover from a variety of control methods. Horizontal roots may extend 15 feet or more and vertical roots may grow six to 15 feet deep. Canada Thistle reproduces by seed as well. The plants are often founds in condensed clusters. Most seeds do not stray very far from the parent plant unless they are floating downstream or caught by a gusty wind.

• There are approximately 5,000 seeds per plant.
• One plant can colonize an area three to six feet in diameter in one to two years.
• Seeds can remain viable in the soil for up to 20 years.
• Small root pieces, approximately 0.25 inches long have enough stored energy to develop new plants. These small roots can survive approximately 100 days without nutrient replenishment from photosynthesis.
• Canada Thistle causes greater crop loss than any other broadleaf weed in Western Canada.

• The best control option is to stop the plant from going to seed.
• Combining control methods is the best way to manage this weed.
• Maintaining desirable plants in the area with Canada Thistle will help to rid of this weed.
• Mowing can be effective if combined with a herbicide treatment.
• If Canada Thistle is in the crop, be sure to exercise a proper crop rotation.
• Persistence is important. Continued stress will exhaust the root system and hopefully kill the weed.
• For herbicide advice, be sure to check your Crop Protection Guide.