Brown Knapweed Found in Horse Pasture Earlier This Fall

Posted: November 2, 2012

A horse owner reported a neurological condition in her horse believed to be caused by the ingestion of Brown knapweed.
Brown knapweed

Brown knapweed

A plant in a Northern Allegheny County horse pasture was positively identified as Brown knapweed (Centaurea jacea) earlier this fall.  Brown knapweed is a perennial that grows 20 to 48 inches tall and has purple or white flower heads.  It is only occasionally found in our region.  Several knapweed and starthistle species exist, and their potential toxicity to livestock seems to vary.  Russian knapweed (Acroptilon repens) and yellow starthistle (Centaurea solstitialis) are plants that are known to be toxic to horses - causing "chewing disease" - but cattle and sheep do not appear to be affected.  The toxicity of brown knapweed is less known, but it is assumed that it may be similar to Russian knapweed or yellow starthistle. 

Initial symptoms of "chewing disease" include having difficulty eating or drinking, as well as anxious or confused behavior.  In the following days, the horse's muzzle, lips, and tongue will be contracted, which is accompanied by constant chewing-like motions of the mouth.  Symptoms can be lessened if the horse is removed from the infested area and treated by a vet.

Horses generally do not like to eat knapweed unless suitable forage is not available.  Horse owners should monitor their pastures and immediately remove their animals from infected areas and provide alternative forage.

For more information, visit or contact Alicia Spangler at 724-548-3447.