Relative Information: The sow thistle is a perennial weed and will tend to grow in the spring from root buds that have been dormant during the winter. It grows in a wide range of climatic conditions. However, it prefers moist soils, therefore riparian areas are ideal. The sow thistle will invade any natural or disturbed areas.

Problems: Decaying sow thistles will tend to excrete a chemical that will prevent seed germination of other species. The sow thistle has an extensive root system that can outcompete native species. During cultivation, small pieces of the roots will produce more weeds.

Chemical Controls:
*all controls are shown in alphabetical order
**Read the label for ingredients, application rates, instructions and safety protocols
¹Overdrive can be mixed with Clearview, Lontrel 360, Navius, and Reclaim II

• 2,4-D Amine and Ester (Top growth only)
• Clearview
• Clearview Brush
• Clearview + 2,4-D amine
• Lontrel 360 (For top growth control)
• Milestone
• Milestone + 2,4-D amine
• Navius
• Overdrive¹
• Sightline
• Tordon 22K
• Truvist

• 2,4-D Amine and Ester (Top growth only)
• Navius
• Reclaim II (Perennial)
• Restore II (Annual and Perennial)
• Overdrive¹
• T22K (Annual)

Mechanical Controls: Somewhat effective. Mowing prevents the production of seeds, however, mowing must be repeated many times due to the long flowering period. Seedlings can be hand-pulled.

Biological Controls: No biological control agents at this time.

Cultivation: Effective for seedlings. Cultivation over long periods can deplete the roots. However, root pieces may give rise to new weeds.

*Grazing: Ineffective. Sow thistle is now palatable to livestock.
*Any grazing on invasive species should not be considered.

Disclaimer:
This is for information purposes only. Please always read and follow the label of each chemical control used (herbicides). For more information on the local policies of chemical use in your area, contact your agricultural division.

This information was made possible by funding from the Southern Alberta Land Trust Society.

Other sponsors of this work include Bayer CropScience, Dow AgroSciences and Alberta Invasive Species Council.

Resources

• Federal Noxious Weed Disseminules of the U.S. - USDA-APHIS

Selected Images

Maps

Invasive Listing Sources

• Alaska Noxious Weeds
• Alberta Weed Control Act
• California Noxious Weeds
• City of Ann Arbor Michigan Parks and Recreation
• Colorado Noxious Weeds
• Hawaii Noxious Weeds
• Idaho Noxious Weeds
• Illinois Noxious Weeds
• Jil M. Swearingen, Survey of invasive plants occurring on National Park Service lands, 2000-2007
• Michigan Noxious Weeds
• National Park Service, Mid-Atlantic Exotic Plant Management Team Invasive Plant List
• Nevada Noxious Weeds
• New Hampshire Invasive Plant Species Watch List
• Nonnative Invasive Species in Southern Forest and Grassland Ecosystems
• Ohio Noxious Weeds
• South Dakota Noxious Weeds
• Washington Noxious Weeds
• WeedUS - Database of Plants Invading Natural Areas in the United States
• Wyoming Noxious Weeds

References