oxalates nitrates repin
Flower Color:
  • flower color
  • flower color
roadsides, fields, haybales, waterside, rangelands, pastures

Time of Greatest Risk


Geographical Distribution

Russian knapweed distribution - United States

Related Species

Russian Knapweed

Centaurea repens

Blueweed, Hardheads, Creeping Knapweed
8/ 10
Russian knapweed (Centaurea repens, previously referred to as Acroptilon repens) is an upright, woody stem perennial.
It emerges in the spring to form spreading branches and produces light pink to lavender flowers which bloom from June to September. It's leaves and stems are covered in gray hairs (knap). C. repens is found in poorly drained and saline/alkaline soils with supplemental water sources such as rivers and streams.

Toxic components
C. repens is toxic to horses, however the exact toxins have not yet been defined. It is thought that repin, a type of sesquiterpene lactone is possibly responsible as it is known to be a neurotoxin. Ingestion of C. repens causes equine parkinsonism (aka chewing disease) in horses. The toxic effects of C. repens are cumulative, which means that poisoning most often results from a build up of toxins in the body over a period of time. Horses must consume large quantities of fresh or dried C. repens prior to reaching the toxic threshold. It is thought that horses must consume at least 60% of its body weight in C. repens prior to clinical signs of toxicity appearing. For an average sized horse, this is 750lb (340 kg) of C. repens. The disease is characterized by the impairment of the horse's facial muscles which inhibits the ability of the horse to bite off and chew food. Horses will often display continuous chewing motions with their mouth. The effects of C. repens are irreversible and prove to be ultimately fatal to the horse.


  • Sudden Onset Of Involuntary Facial Movements
  • Continuous Chewing Movements
  • Jaw Held Open Or Tightly Closed
  • Dehydration
  • Severe Weight Loss
  • Frequent Yawning
  • Headshaking
  • Depression
  • Appetite Loss
  • Difficulty Breathing
  • Submerging Head In Water To Drink.


MECHANICAL: Use mowing in combination with herbicide treatments than tilling. Hand-pull only when wearing gloves.

BIOLOGICAL: Russian knapweed gall nematode


ChemicalTrade NameApplication Rate (Amount/Acre)Time of Application
PicloramTordon 22k1 to 2 qtEarly flower to frost
Clopyralid 2,4-DCurtail1 to 2 qtFull bloom to frost
ClopyralidReclaim2/3 to 1 1/3 ptFull bloom to frost
ImazapicPlateau12 ozFall to winter
AminopyralidMilestone5 to 7 ozFall to winter
ChlorsulfuronTelar XP1 to 3 ozPrebloom to bloom and fall rosette
Aminopyralid + MetsulfuronChaparral2 1/2 to 3 1.3 ozSpring or fall