These seeds remain viable for a number of years, compounding the difficulty of control efforts. Both diffuse and spotted knapweed are considered pioneer species. Any soil disturbance may provide a suitable site for germination and growth of knapweed. Soil nutrient depletion by knapweed allows a single species stand and prevents more valuable forages and native plants from encroaching upon the knapweed. Spotted knapweed often forms dense stands while diffuse knapweed tends to be more patchy in distribution.
Knapweeds have little nutritive value and possess a high amount of fiber.
Plant spines may cause injury to mouth and digestive tracts of grazing animals. Rosettes are not grazed, although flower shoots are utilized in overgrazed areas. Sheep may allow for more flexibility in grazing management. High consumption levels of knapweed can be toxic to certain livestock such as horses. Chemical control is effective in reducing the weed infestations in some areas.