Plant friends and foes

Spotted Knapweed:
Pretty and Poisonous

Terry Bonace

Spotted Knapweed

Spotted Knapweed (Centaurea biebersteinii) resembles a diminutive thistle (without the prickles) or pink bachelor’s button. But in spite of its small size, this plant has potential to cause great harm in the Indiana Dunes ecosytem. You can find it blooming in Beverly Shores along disturbed road and trail sides and in bare sand in mid summer to early fall.

Basal Rosette, First Year Knapweed

Unlike many of the plants discussed in this column, spotted knapweed was not introduced as an ornamental or wildlife food and cover but instead arrived by accident. It is believed to have been first introduced from Europe in an alfalfa and clover seed shipment to Washington in the late 1800s. Now it is found in 45 of our 50 states. Spotted knapweed is not much taller than 3 feet and its flower heads are only a few inches wide. The pink fringe of the flower sits like a wide brimmed hat on the top of a pineapple-shaped base. The bracts on the base have dark tips, giving it a spotted appearance and hence the name, spotted knapweed. It has silvery foliage and narrow, inconspicuous leaves. Like most biennial plants, in its first year it forms a rosette of deeply lobed, silvery leaves close to the ground and only begins blooming its second year. It can, though, in this short period produce nearly a thousand seeds from a single plant.

Field of Spotted Knapweed

The chief danger of spotted knapweed is that it can be poisonous to other plants. It carries toxins in its leaves and stems that eliminate its native plant neighbors. Though it has not yet achieved the prominence locally of some weeds, I think it is worth discussing, having seen acres and acres of spotted knapweed meadows in our Sleeping Bear Dunes National Lakeshore, to the north. The potential for such widespread distribution exists in the Indiana Dunes too. Noel Pavlovic, Research Ecologist at the U.S. Geological Survey Great Lakes Science Center, told me that spotted knapweed first entered the Indiana Dunes in 2000 by way of train track rights-of-way coming from the western United States. It then traveled by way of roads and the South Shore tracks to the eastern unit of the National Lakeshore. The Lakeshore has been monitoring it carefully since its arrival to prevent its spread into the dunes where it could threaten many of our native plants, including the federally endangered Pitcher’s thistle.

The best way to control small populations of spotted knapweed in Beverly Shores is by hand pulling. This is even more effective with a digging tool to get more of the tap root. But because of the toxins the plant contains, use gloves to pull it.

The Environmental Restoration Group (ERG) will be glad to help identify plants for you and make suggestions for removal and for native replacements. Don’t hesitate to contact Terry Bonace (tbonace@gmail.com), Candice Smith (cmsmith2@umail.iu.edu), or Bill Schaudt (blschaudt2@gmail.com) for assistance.

Beverly Shores Environmental Restoration Group,
P.O. Box 667, Beverly Shores, IN 46301