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. However, the applied cost of the chemicals does not make it cost effective for a large acreage of infested rangeland requiring control measures. Treatment near bodies of water is prohibited by law and retreating of treated areas is often necessary due in part to newly germinated seedlings from the large soil seed bank.
Biological control offers the potential of controlling the weeds in a safe, cost effective method.
Numerous biological control organisms have been either imported for studies or for actual release against the knapweeds. A number of them have already been established in the United States and Canada. By themselves, it is doubtful whether one organism would exert enough pressure on the plant population to effect any significant control. However, as a complex of biological agents, the effect should be enhanced. Diffuse knapweed roots Larval feeding of this wood boring beetle within the root crown effectively stops rosette growth and delays bolting for one or more years.