It seems to be especially problematic in the central sands, northern Wisconsin, and near the Great Lakes. Spotted knapweed reproduces solely by seed. Individual flower heads bloom from late June through August for 2-6 days each. The bracts reopen after about 20 days and scatter seeds. Plants average about 1,000 seeds per plant.
Seeds are viable for seven years, and germinate throughout the growing season.
Seedlings emerging in fall develop into a rosette of leaves that resume growth in spring. Knapweed tends to dominate sites at the expense of community diversity or forage production. Knapweed infestation can also increase surface run-off and sedimentation. Caution is also necessary when using hay from the road ditches of primary roadways, or hay purchased from known infested areas. Outlying plants should be controlled before main populations.