Ministry of Agriculture, Food and Rural Affairs

Table of Contents

Names

•English - spotted knapweed, black knapweed, brown knapweed, russian knapweed, diffuse knapweed
•French - centaurée maculée, centaurée noire, centaurée jacée, centaurée de Russie, centaurée diffuse
•Latin - Centaurea maculosa Lam., Centaurea nigra L., Centaurea jacea L., Centaurea repens L., Centaurea diffusa Lam.

Photos

Figure 1 - Black Knapweed

Figure 2 - Spotted Knapweed

Current Status

•Ontario Weeds Act - noxious
•Other provinces - noxious in Alberta, BC, Sask, Man (Russian); Alberta, BC, Sask, Man (spotted); Alberta, BC, Sask, Man (diffuse);
•Canadian Federal Seeds Act - Class 1 (Russian, diffuse, spotted)
•U.S. Federal Noxious Weed - no
•U.S. Noxious State Reg - 24 states (including Indiana, Mich, Minn, NY); black - 2 states; spotted - 14 states (including Mich, Minn)' brown - 1 state; diffuse - 12 states (all western states)

Poisonous/Cautions

•Pub 505 - no
•NE Weeds - no
•Canadian Poison Plant - not listed
•Cornell Poison Plant - not listed

 

Distribution

•Mostly found in western Canada and USA. Black is found in southern Ontario. Brown is found mostly in the western areas of southern Ontario. Russian is known to occur in central Ontario. Spotted can be found throughout Southern Ontario especially in Grey and Hastings. Diffuse is not commonly found in Ontario. Frequently grows in shallow top soil areas.

 

Growth Habit

•Perennial, Spotted is biennial or short lived perennial

 

Method of Propagation

•Seeds

Control

•Very difficult to control. Not listed on any labels except for diffuse knapweed on the Banvel label. Close mowing at the bud or flowering stage can reduce infestation (June to October) but flowering stems may regrow. Shallow cultivation is not effective but deep plowing (18 cm) followed by vigorous establishment of grasses can reduce the infestation.