RUSSIAN KNAPWEED — Centaurea repens L.

Asteraceae — (Sunflower family)

Russian Knapweed might be referred to as a “steam roller” on the noxious list because it has the ability to completely overrun an area if not contained.  Russian Knapweed is poisonous to horses affecting the liver and is not grazed by other livestock if another choice exists.

Seeds germinate the first year to become several, thin, inch long, grey green leaves that are covered with a fine hair or nap.  The second year is the same with the growth of several two to three foot branching stems, topped with lots of pink (or white), seed producing flowering heads.

The plant has a tap root 8 ft long or more, and a system of creeping horizontal roots that produce many more plants.  The roots are generally covered by a black sheath. 

The plant is spread by plowing.  Spray with “Milestone” before flowering and in the fall or pull and burn to destroy all seeds.  If you have small patches of Russian knapweed, control them immediately. You can not be too careful to destroy this weed and keep a good watch out for it.

The following is courtesy of Weeds of the West:
Russian knapweed is perennial, forming dense colonies by adventitious shoots. It reproduces by seeds and creeping, horizontal roots. Roots, which are both vertical and horizontal in the soil, may or may not be black with a scaly appearance. The ridged stems are erect, rather stiff, openly branched, eighteen to thirty-six inches tall. Young stems are covered with soft gray hairs or nap. Leaves of newly emerging plants are toothed and covered with fine hair, giving them a blue-green color.

Lower leaves are deeply lobed, two to four inches long; upper leaves entire or serrate, narrow to a sessile base. The upper leaves are small and narrow with broken edges. Leaves attached midway up the stem have slightly toothed margins, while basal leaves are deeply notched. Cone-shaped flowering heads are ¼ to ½ inch in diameter, are thistle-like, solitary, terminal at the tip of leafy branchlets. Flowers are white to lavender. Many pearly involucral bracts form with rounded or acute papery margins.

Russian knapweed is a native of Eurasia, probably introduced in North America about 1898. It is now widely established in the Western United States. This species forms colonies in cultivated fields, orchards, pastures and roadsides.

Flowering occurs from June to September and seed is produced in late summer to early fall.

Growth Habit: Perennial herb, up to 3` tall, erect, may be in dense clumps. Grayish color.

Leaves: Alternate, simple, of several types: Upper leaves – small, narrow, unbroken edge; Stem leaves – intermediate in size, slight toothed margins; Basal leaves – deeply notched.

Stems: Numerous branches, each ending with a single flower.

Flower: Single, terminal, lavender, thistle like, scaly seed head.

Roots: Dark brown to black and heavily scaled.

Seeds: Flattened, ivory colored, retained in cup-shaped seed heads.

Other: Leaves and stems covered with short stiff hairs giving plant an appearance of knap. Spreads by seeds and creeping rootstocks.

(Courtesy of Weeds of the West)

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