People are the main reason knapweed is spreading across the country. Seeds are being transported by vehicles, contaminated hay, livestock, and wildlife. The park has spotted knapweed along road corridors and at the Painted Canyon Visior Center area. Luckily the plant is easy to control if we can find it early. The most effective treatment for knapweed is to apply herbicide.
Biological controls are available but their success has been limited.
Canada thistle is an aggressive, creeping plant that infests hundreds of acres of park land and over 500,000 acres in the state of North Dakota. Generally, the plant infests disturbed ground, reducing forage for wildlife. One plant can colonize an area of 3 to 6 feet in diameter in one to two years. Established Canada thistle is difficult to control. Canada thistle is a native of north Africa, Europe, Asia and Scandinavia through Siberia.