– Christine Gelley, Agriculture and Natural Resources Educator, Noble County OSU Extension
Don’t confuse knapweed (bottom) with chicory (top).
Driving the roads of Southeast Ohio last week was like getting a “while you were out” memo after returning from a week in Texas. The difference a week can make in the landscape can be drastic. The impacts of severe drought are visible, and we are all wishing for more rain. Hopefully this week will bring some relief and we’ll see pastures, hayfields, and lawns green up again soon.
Nothing lasts forever, but even when conditions improve, the impacts of this dry season will continue to cause a ripple of impacts over the next six months. As many livestock producers are already dipping into their hay supplies to supplement poor pasture conditions and second cutting is skimpy, I am concerned about what will happen with our winter hay supplies. If you are looking for resources pertaining to drought, visit https://go.osu.edu/ohiodrought for the latest updates on drought conditions in Ohio and click on the tabs pertaining to your areas of interest to find suggestions for coping with the stress drought can cause.
One plant that doesn’t seem phased by drought is our dreaded foe- Spotted Knapweed. The magenta blossoms it produces taunted me Saturday morning as I made my way around the northeast corner of Noble County visiting friends. I have been watching and waiting for knapweed to bloom all summer and here it went and started blooming when I was away. It is annoyingly pretty. Many people see it and think, “what a nice wildflower” and move on with their lives not realizing how harmful this pretty invasive plant can be.
Not familiar with spotted knapweed yet? Let’s review what it is and why we care.
Spotted knapweed is a detrimental weed that shares similarities to many less threatening plants. 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, just a rosette of five to twelve irregularly lobed hairy leaves. The plant will flower in the second year and continue to flower in the years following. Mature plants may be one to four feet in height, slender or bushy, and will have a deep taproot. It is quite attractive to a variety of pollinators but should not be propagated or preserved in the landscape for this purpose. Many other wildflowers with fewer risks are equivalent food stocks for pollinators.
Spotted knapweed is a prolific seed producer, so if knapweed is not addressed in year two, a population explosion may occur in year three. It gets the name “spotted” because the flower receptacle bracts have dark brown tips. Knapweed is aggressive because it has few natural predators in Ohio. Allelopathic compounds have been isolated from knapweeds, which are chemical substances that can leach from plants into the soil and weaken competitors, but the severity of the allelopathic potential remains under investigation. Animals are unfamiliar with it, so grazing as a control is ineffective and it thrives on marginal soils. It can easily outcompete weak stands of desirable plants for nutrients.
The best control tools for spotted knapweed and many other weeds 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 including a combination of management tactics.
For more details about spotted knapweed and control strategies contact your local Extension office.