Noxious Weeds Profile - Knapweed spp.
Table of Contents
English - spotted knapweed, black knapweed, brown knapweed,
russian knapweed, diffuse knapweed
Figure 1 - Black Knapweed
Figure 2 - Spotted Knapweed
Ontario Weeds Act - noxious
Pub 505 - no
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.
Perennial, Spotted is biennial or short lived perennial
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.
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