Spotted Knapweed

Spotted Knapweed (Centaurea stoebe)

Origin/Introduction:

Spotted knapweed originated in Europe and Asia. It was first brought to North America in the 1890s as a contaminant in agricultural seed and in soil discarded from ship ballast. Since then, this species has seriously impacted pastures and most rangelands of the United States.

THREATS/IMPACTS 

This noxious weed rapidly colonizes disturbed areas. Spotted knapweed produces a substance that is toxic to other plants causing it to spread quickly and establish. The highly invasive nature of this plant decreases the biodiversity of the environment.

IDENTIFICATION:

Spotted knapweed can grow up to 2-4 feet tall and has a long tap root that anchors it in the ground. The plants’ stem has various branching. It has grayish-green leaves that are somewhat like hair, deeply lobed into narrow segments and a pink/purple oval flower. The flower has a bract that is stiff and is marked with upside down “V”s, producing a spotted like appearance. These flowers bloom from June to the end of August.

Control/Management:  

Controlling efforts depend on the size of infestation.

Manual Control: 

Continuous hand pulling can be effective when controlling small patches of spotted knapweed. It’s crucial to remove as much of the tap root as you can to prevent regrowth. To prevent skin irritation, wear long sleeves and gloves.

Mowing before the plants flower can prevent them from producing seeds. Although, they flower throughout most of the spring/summer so it’s necessary to mow multiple times to reduce the possibility of resprouting and seed production.

Chemical Control:

Herbicide use has been successful for larger patches. Applications should be applied during early spring and late fall in order to target rosettes. Typical herbicides used include clopyralid + 2,4-D (Curtail) and clopyralid + triclopyr. All herbicides should be applied according to label instructions.

Biological Control:

Multiple insects and fungi have been introduced to control spotted knapweed. More information about spotted knapweed biocontrol can be found in the U.S. Forest Service’s Biology and Biological Control of Knapweed Guide.

(https://www.invasive.org/weeds/knapweedbook.pdf)

Get Involved

Aid Early Detection Efforts

Searching for invasive species populations in an effort to detect their presence before their populations become too large to manage is vital to reducing the impacts of invasive species on our natural ecosystems.

Click the link below to learn more about the species we’re enhancing early detection efforts for and to join our invasive species Volunteer Surveillance Network to aid this effort (training will be provided).

Report Invasive Species

NYiMapInvasives is an online, collaborative, GIS-based database and mapping tool that serves as the official invasive species database for New York State.

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Sources:

Centaurea stoebe (spotted knapweed). Minnesota Wildflowers. (n.d.). https://www.minnesotawildflowers.info/flower/spotted-knapweed

Spotted knapweed. Minnesota Department of Agriculture. (n.d.). https://www.mda.state.mn.us/plants/pestmanagement/weedcontrol/noxiouslist/spottedknapweed

Spotted knapweed. WNY PRISM. (2023, March 3). https://www.wnyprism.org/invasive_species/spotted-knapweed/#:~:text=Spotted%20knapweed%20is%20an%20herbaceous,of%20its%20many%20branching%20stems.

Spotted knapweed control. King Washington State Noxious Weed Control Board. (n.d.). https://www.nwcb.wa.gov/images/weeds/Spotted-Knapweed-control_King.pdf

SLELO PRISM GOALS

PREVENTION
Prevent the introduction of invasive species into the SLELO PRISM.

EARLY DETECTION & RAPID RESPONSE
Rapidly detect new and recent invaders and eliminate all individuals within a specific area.

COOPERATION
Share resources, including funding personnel, equipment, information, and expertise.

INFORMATION MANAGEMENT
Collect, utilize, and share information regarding surveys, infestations, control methods, monitoring, and research.

CONTROL
Control invasive species infestations by using best management practices, methods and techniques to include: ERADICATION (which is to eliminate all individuals and the seed bank from an area), CONTAINMENT (which is reducing the spread of established infestations from entering an uninfested area) and SUPPRESSION which is to reduce the density but not necessarily the total infested area.

RESTORATION
Develop and implement effective restoration methods for areas that have been degraded by invasive species and where suppression or control has taken place.

EDUCATION & OUTREACH
Increase public awareness and understanding of invasive species.

INNOVATION
Develop and implement innovative technologies that help us to better understand, visualize, alleviate or manage invasive species and their impacts or that serve to strengthen ecosystem function and/or processes.