Spotted Knapweed Still Lingers

Christine Gelley, AgNR Educator, Noble County, OSU Extension

On a drive to Zanesville yesterday I was unhappy, but not surprised to see spotted knapweed continuing to put out fresh, pretty, flowers along the roadsides. To do my civic duty, we will talk about spotted knapweed once more before the growing season ends. Tell your friends in the neighborhood watch program to keep this plant from going to seed. Frost is not far off, maybe some will meet their demise by the dropping temperatures, but I would not bet money on it.

The color of the flower is similar to that of red clover, the growth habit is similar to chicory, and the flower shape is similar to Canada thistle and ironweed. Two other plants that could be confused this time of year are New England Aster and Billy Goat’s Weed.  However, the combination of growth habit, color, and flower shape is unique to spotted knapweed.






Photo Caption: Step #1 for treatment of spotted knapweed is accurate identification. Spotted knapweed (upper left) is often confused on first glance with other flowers like red clover, chicory, or ironweed. Growth habits are drastically different between all of these plants. (Photo Sources: Steve Dewey of Utah State University and Christine Gelley of OSU Extension)

The best tools for spotted knapweed control are early detection and early action. Hand pulling and spot spraying young plants that are few and far between can be effective on new invasions. However, heavy infestations will likely take a more creative and lengthy approach to treat.

Knapweed is a forb that is responsive to multiple broadleaf herbicides. Mowing is marginally successful. It does help prevent the development of seed, but it is able to flower below the height of the mower deck. Chemical treatment has been successful in grass pastures of our region if timed appropriately. There are biological controls being developed for spotted knapweed too, but they are primarily used in the Western States that have been dealing with this weed for decades already. Demand is high and supply is low.

Knapweed is aggressive because it has few natural predators in Ohio. Animals are unfamiliar with it and it thrives on marginal soils. It can outcompete weak stands of desirable plants for nutrients. You can learn more about spotted knapweed in Ohio on YouTube. Extension Educators, Clifton Martin of Muskingum County and myself, broadcasted an informational interview about spotted knapweed as part of a video series called “Forage Focus” in September 2018. It can be viewed at

Knapweed in the basal rosette stage. Photo:

If you come across something you suspect might be spotted knapweed, please contact your County Extension Office for assistance with identification. Consider enrolling in the STOP program.

The Spotted Knapweed Treatment for Ohio Producers (STOP) Project is funded through the Regional Conservation Partnership Program (RCPP), which is administered by the Natural Resources Conservation Service (NRCS). Landowners of Noble, Guernsey, Muskingum, and Morgan County are eligible to apply for cost recovery funds to treat spotted knapweed in pasture and hayfields.

To learn more about the STOP Project or to submit an application, visit your local USDA Service Center or visit the NRCS website and select “Get Started with NRCS”.