Diffuse Knapweed
(Centaurea diffusa Lam.)
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MATURE PLANT
* 1-2 feet tall |
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ROSETTE
* finely divided covered with short hair |
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FLOWER
* ¾-1 inch diameter |
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INFESTATION
* approx…2500 acres in El Paso County | |
Diffuse Knapweed, (Centaurea diffusa Lam.) is a member of the Aster family, Thistle tribe. It is a biennial or short-lived perennial plant that reproduces only by seed. The plant usually produces a single main bushy stem that is 1 to 2 feet tall. A basal rosette of greyis-green leaves is present in young plants with each leaf divided into narrow segments. When leaves are young, a thin nap is present.
Stem leaves in the mature plant become much reduced as you ascend to the tip and alternate one per node. Flowers are mostly white, sometimes pink to lavender, and are located on each branch tip. The bulb (involucre) below the blossom has sharp, blond points (bracts).
This plant will take over your land and yard at which nothing else will grow. It likes overgrazed or people-disturbed land, sandpits or roadsides. Tires are another means of spreading the seeds.
To control this plant keep it from going to seed. Diffuse knapweed will not tolerate shade and flooding. It likes 9" to 16" moisture per year. Sheep, goats and cattle will consume diffuse knapweed. Avoid overgrazing to preserve competitive grasses. The pulling and spraying of the weeds will help with controlling, along with planting perennial grasses in the fall.
Fertilize and irrigate new grasses to stimulate grass competition. Tilling is not a recommended control, because it creates an ideal seedbed. Mowing will make it go prostrate and still will produce seed. Seed only germinates in the spring and fall.
The plant will not tolerate flooding or shade.