Field Guide to Plants Poisonous to Livestock: Western U.S.
Common name: Russian knapweed
Region: W and upper Mid-W U.S.
Habitat: Waste areas, roadsides, overgrazed areas, hay fields
Toxic season: Summer and fall
Features: Stiff, spreading, branched plant up to 3' tall. Base leaves deeply lobed, lance-shaped, toothed, hairy, 2-4" long; upper leaves are numerous, thin, lance-shaped, 1" long, narrowing at stem, may or may not be toothed. Flowerheads 1/4-1/2" across, cone-shaped, pink or purple in whitish, paper-like, urn-shaped bracts. Fruits are seeds with many white bristles.
Poison type: Unidentified sesquiterpene lactone Signs/effects: A type of irreversible brain damage causes "chewing disease" characterized by inability to chew or use lips normally, inappropriate chewing, yawning, standing with head down, aimless walking, head pressing, difficulty breathing. Initially animal may be aggressive. Signs usually occur abruptly after 1-2 months of cumulative ingestion of at least 60% of body weight.
Treatment: No known treatment. Animals will not recover. If diagnosis certain, euthanasia is generally recommended.
Comments: Horses known to be susceptible. Toxic whether fresh or dry. Generally grazed only if adequate other forage unavailable, but may be eaten in hay.
© Copyright 1998 by Shirley A. Weathers