A long-term control using biological agents is being sought. If you've ever pulled a dandelion and thought it had a long root, imagine trying to get rid of a plant that has roots that can extend 35 feet, grows through asphalt, and flings its seeds 15 feet. It's leafy spurge, and it invades prairies, roadsides, and pastures. In places such as Lake Bronson State Park it outcompetes native grassland flora. Its deep root system enables it to survive dry conditions and resprout even after the foliage is destroyed.
Control usually combines use of herbicides, prescribed fire, and mowing.
Insects for biological control have been released at several hundred sites in the state by the U.S. and Minnesota departments of agriculture. Spotted knapweed probably arrived here in alfalfa or hay seed from Europe and Asia. It reproduces solely by seed. Dry prairies, oak and pine barrens, and sandy ridges are likely natural habitats. Chemical control can be fairly effective but cost prohibitive.