Description Spotted knapweed generally is a short-lived perennial, reproducing solely by seeds. The seeds may germinate from spring through early fall. The plant grows 2 to 4 feet tall and bears alternate, pale green leaves which are 1 to 3 inches long. Leaf margins of the lower leaves are divided and smooth while the surface of the leaf is rough. The upper leaves are linear in shape.
Stems are erect and rough, with slender branches.
Numerous flowers are produced from early July through August. Russian knapweed flowers are smaller than those of spotted knapweed and do not have black mottling on the flower bracts. Spotted knapweed flower. Management People are the major cause of spotted knapweed spread. The weed is spread readily in hay and on vehicle undercarriages.