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MuskThistle (Carduus natans L.)

Crop Impacts: Pastures

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About Musk Thistle:

Musk Thistle is a biennial weed that is reproduced by the release of its seeds and has a two year life span. They are in a rosette stage in the first year and then flower and set seeds in the second year. Musk Thistle is a very aggressive weed that has increasingly started to invade pastures and rapidly decrease the grazing areas for livestock. This is due to the fact that each plant can produce up to 50 flower heads with each flower producing about 50 to 80 seeds each, coming to a grand total of approximately 2500 to 4000 seeds per plant.

Family: Composite or Aster Family (Compositae)

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Musk Thistle Scouting and Prevention:

The first year plant is a large, flat rosette in a shape similar to a circle. Each leaf of a first year plant is about 12 inches long and 4 inches wide with bright green to gray-green in colour. The margins of these young leaves are deeply lobed with long, sharp spikes going in all directions. The second year plants have an erect stem that can stand between 1 and 6 ft. tall, with very spiny, lobed, leaf-like wings going lengthwise on all branches and stems, except for the area below the flower head. These shoots start to grow in early May and reach full maturity in early June. The most predominate feature of this weed is its flower, which produces from June to October. Musk Thistle has single flower heads that are about 4 to 7.5 cm wide and sit on thin, smooth, and long stalks. They are large, bright purple disk flowers that are surrounded by broad-based, greenish brackets with outward pointing sharp spines. The seeds produced by the two year old Musk Thistle are light brown, shiny, egg-shaped and about 4mm long with light hairs coming from the tip.

Common locations

  • - Coarse-textured soil
  • - Pastures

Prevention

Prevention of Musk Thistle is less expensive and less time-consuming then trying to control it. Contaminated hay is the main source of the spread of Musk Thistle. Make sure when you seed a new area that you do so with certified weed-free seeds. It is also very important that you prevent overgrazing by livestock to help desirable grass stay strong and dense. If there is an infested area on your property, be sure to drive around instead of through it. Make sure to give all equipment that has been in infested fields a good clean so that no seeds are transferred.

Musk Thistle Control:

Cultural Control

The key to controlling Musk Thistle is not to let it seed. A good way to deal with this is to mow after the stems have started to grow, but before the flowers open. However, regrowth may occur, in which case a second and maybe even third mowing of the infested area might be necessary.

Chemical Control

The best time to apply herbicides to Musk Thistle is in early spring or late fall, when the rosettes are present but the stocks have not yet appeared. It is important to know that the younger the rosettes are, the easier it is to control with herbicides. The rosettes must be treated when they are actively growing and not under stress. The most commonly used and cheaper herbicide is 2,4-D and is most effective when it is applied 10 to 14 days before the stems are produced in the spring. Dicamba and piclorma herbicides have better control over Musk Thistle when is has started to grow its stem. Dicamba can be applied in early spring for good control. Also, Dicamba at 1/4 pound per acre combined with 2,4-D at 1/2 pound per acre can give up to 97% control in late fall. Piclorma by itself or in combination with either Dicamba or 2,4-D has the best late-season control but is the most expensive herbicide control for Musk Thistle. It does have restrictions in the fact that it cannot be sprayed near water. It does; however, provide great control in cool, dry weather. Due to the fact that Musk Thistle seeds can lie dormant in the ground for several years, it may take 2 or more years of herbicide application to have full eradication of this weed.

Latin / Alternative Musk Thistle names:

  • - Carduus natans L.,
  • - Nodding thistle
  • - CRUNU
  • - Chardon penché

Additional Musk Thistle Resources

http://www.omafra.gov.on.ca/english/crops/facts/ontweeds/nodding_thistle.htm

http://www.agry.purdue.edu/ext/forages/publications/ws-19.htm