– Christine Gelley, Agriculture and Natural Resources Educator, Noble County OSU Extension
Don’t confuse chicory (top) with spotted knapweed (bottom).
A detrimental weed that has been heavily on the agricultural radar in recent years is currently blooming in Noble and some surrounding counties. Its name is spotted knapweed. Everyone in Noble County should be aware of this plant and be working to remove it from sensitive areas. While the flowers are pretty and it is attractive to pollinators, it is not a plant that we want in our landscapes.
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. However, the combination of growth habit, color, and flower shape is unique to spotted knapweed. Spotted knapweed may possess as many as 200 pink to purple blooms per plant. The mature seed heads resemble Canada thistle, a tight cluster of seeds with a fluffy pappus attached. The pappus helps the seed move with wind, water, animals, and vehicles.
Step #1 for treatment of spotted knapweed is accurate identification. Spotted knapweed (far 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)
This weed is similar to a biennial, in that the first year of growth there is no flower. The plant will flower in the second year and continue to flower in the years following. It is a prolific seed producer, so if knapweed is ignored in year two, you can experience a population explosion in year three.
Knapweed grows in many different soil environments
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.
Knapweed is aggressive because it has few natural predators in Ohio and has allelopathic properties that can weaken neighboring plants. Animals are unfamiliar with it and it thrives on marginal soils. It can easily out compete weak stands of desirable plants for nutrients.
Hand pulling or spot spraying young plants can be effective on new invasions.
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.
If you come across something you suspect might be spotted knapweed but are unsure, please contact me at the Noble County Extension Office or your County Extension Educator for assistance with identification and corresponding treatment.
It’s not uncommon to find spotted knapweed along the roadside