Eagle County Weed of the Week: Spotted Knapweed | VailDaily.com

Eagle County Weed of the Week: Spotted Knapweed

Daily Staff Report
Vail CO, Colorado
Special to the Daily/John Cardina, Ohio State UnivSmooth leaf margins and urn-shaped flowers are key to identifying Spotted Knapweed.

EAGLE COUNTY” This week’s weed of the week is Spotted Knapweed (Centaurea stoebe).


– Short lived perennial growing from 1-foot to 3-feet tall.

– Flowers are purplish-pink, urn or vase-shaped, about 1/2-inch to 1-inch tall with dark comb-like bracts under the bloom.

– Knapweed flowers could be mistaken for some thistles, but the leaves are smooth and oblong as opposed to the deeply-lobed thistles.

– Spotted Knapweed can be distinguished from other Knapweeds by the dark tips on the bracts of the flower.

– Reproduces entirely by seeds that can remain dormant for up to 8 years.

– One plant can produce 140,000 seeds.

– Leaves are light green in color, deeply lobed with small hairs.

– Contains allelopathic chemicals (its own herbicide) that prevent other species of plants from growing around it.

– Capable of producing dense monocultures.

– Knapweed seeds are often spread in hay and on vehicles.

– Cutting or mowing Spotted Knapweed before the plant sets seed will minimize the number of seeds the plant produces, but will not get rid of the infestation.

– Long term mowing can reduce large populations of this plant over a period of time, but must be repeated often and is not recommended. Pulling smaller batches of Spotted Knapweed will be effective, but the area must be revisited several times throughout the summer as well as in years to come.

– Gloves are a must for all of the noxious weeds, but especially Spotted Knapweed since skin irritation and other symptoms are a common occurrence. It is also advised to wash your hands and any skin that has been exposed to Spotted Knapweed.

– Herbicides are recommended for larger infestations. Call Eagle County Weed and Pest or a licensed applicator for suggestions on what herbicide to use and the proper handling of those herbicides.

– Seeding an area with native grasses after removing Spotted Knapweed is essential in avoiding a re-infestation. As with all noxious weeds, the most successful way to control Spotted Knapweed is preventing its establishment.

For more information on these plants and the Weed Management Programs in Eagle County visit http://www.eaglecounty.us/weed or http://www.vailgov.com/weeds. Or call the Eagle County Weed and Pest Department, 970-328-3540, the Town of Vail Department of Public Works 970-479-2158, or the Eagle County Extension Office 970-328-8630.

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