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Russian Knapweed (Centaurea repens)

Status:

Listed Noxious Weed In Montana & North Dakota

History:

First Montana Specimen Collected 1

    

County:

Fergus

Year:

1934
“Russian knapweed is native to Mongolia, Russian Turkistan, Iran, Turkish Armenia and Asia Minor. Seeds of Russian knapweed were present in alfalfa seed imported from Russian Turkistan beginning in 1898 and 1899. An estimated 500,000 acres were planted with commercial Turkistan alfalfa in the United States. Once imported, it spread widely by sale of domestically produced alfalfa seed or hay containing weed seeds. It was first reported in the Northwest in Yakima County, Washington in 1922 and in Fergus County, Montana in 1934. By 1991, the weed was recorded in every county in Montana and infests an estimated 51,000 acres.” (Duncan, Story, &amp; Sheley)    
   
   
   
   
   
   
   
   
   
   
   

Habitat:

 

Perennial herb, up to 3 ft. tall, erect, may be in dense clumps.

 

Growth Habit:

 

Perennial herb, up to 3 ft. tall, erect, may be in dense clumps.

 

Leaves:

 

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

 

Stem:

 

Numerous branched, 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 Notes:

 

“Although Russian
knapweed is closely related to the spotted and diffuse knapweeds, there
are some distinct differences too, enough differences that it is sometimes
considered a different genus, Acroptilon repens. Instead of emphasizing
mass seed production like the other knapweeds, Russian knapweed puts much
of its energy into a deep and spreading root system. New plants shoot up
from the roots, forming dense patches of cloned plants. Thus the plant is
slower to establish, but more difficult to eradicate than the other
knapweeds. The plants are long-lived perennials, known to live more than
75 years. It favors poorly drained and alkaline/saline soils, but does not
do well in dense shade or severe drought. Russian knapweed infests about
47,000 acres of rangeland in Montana.”


“Russian knapweed contains sesquiterpene lactones, which can cause
irreversible brain damage in horses, a disorder called "chewing disease"
(equine nigropallidal encephalomalacia). Affected horses are unable to
chew or use their lips normally; It is also characterized by yawning,
standing with the head down, aimless walking, head pressing, and
difficulty breathing.&nbsp; The disease has occurred in horses that consumed
more than 60% of their body weight of the weed within 1-2 months. There is
no known cure, and death results from starvation or dehydration. The
plants are toxic wet or dried. Horses only graze on Russian knapweed if no
other forage is available, or if it is included in hay.” (Elpel)