Canada Thistle

Cirsium Arvense

What is it?

Canada thistle, or Cirsium Arvense, is a perennial non-native plant that has a very deep root system. These deep, horizontal roots, allow the plant to aggressively creep and spread out into new areas. It was introduced from Europe and it is a member of the Aster or Sunflower family. Also, Canada thistle spreads itself through its seeds. It can grow to be 2 to 4 feet high, and its leaves are spiny, bright green, oblong in shape, and slightly hairy on the undersurface of the leaf. Its flowers are about one centimeter in diameter and are tubular in shape. They form on the ends of branches and exist in small clusters, one to five per plant, and vary in color between white and purple. Female species of Canada thistle have a strong vanilla scent.

Why is it a problem?

Canada thistle is problematic due to its creeping root system it can spread fast and quickly form dense stands. Every piece of its root varies from ½ to 1 inch in length, and carries the capability to form new plants. It is also a problem because it can infest many different land types, ranging from riparian zones, to ditches, to pastures, to irrigated cropland, to roadsides, and even to productive dryland cropland. Canada thistle can substantially reduce forage production because cattle do not graze near areas of infestation.

Management techniques:

The most effective way to manage Canada thistle is by combining methods of control:

According to the CSU Extension, the most important control method is considered to be prevention. Once Canada thistle has invaded an area, its weeds should be stressed on a continual basis. Stressing the weeds can cause the storage of nutrients in its roots to run out and then the plant may eventually die.
When it comes to farming and ranching, maintaining healthy pastures and rangeland will aid in the invasive’s management. Property should be continually monitored for any new infestations that may occur.
It is important to avoid bare ground due to overgrazing because bare spots are a prime habitat for weed invasions to occur.
Herbicides can be used in the Fall, after cattle, goats and sheep have grazed on the lands because these animals will graze on Canada thistle when it is young and succulent during the spring.
Mowing areas where Canada thistle has spread can be an effective management tool because hand-pulling the plant is not possible due to its extensive root system. Mowing should be done every 10-21 days throughout the growing season.

What can we do?

The most important thing that we can do is to prevent Canada thistle in this area. Simply knowing what it looks like and some general facts about it can he helpful. Once it has impacted an area, we can try to control it from spreading. Reporting places where you find Canada thistle to an agricultural agency can also be a useful method of prevention and control.

Entities working on this invasive in the Gunnison Basin:

Canada Thistle is included in the BLM and Noxious Weed Plan. A hard copy can be reviewed at the BLM Gunnison Field Office located at 210 West Spencer Street, Gunnison, CO 81230.

The USFS is doing research in collaboration with other agencies in the Gunnison Basin to perform monitoring, management and research on these invasive species in regards to Canada Thistle. However, there is not any specific research or publications on these species at the moment, if you contact the USFS at 970-641-0471, they can provide you with information.

General Information on Canada Thistle:

Colorado State University Extension

Website that provides identification, biology & control of Canada Thistle.

Colorado State University Extension

PDF, that provides information about Canada Thistle and management techniques

Colorado Weed Management Association

Website that provides information, habitat, identification, impacts, biology and control of Canada Thistle