General poisoning notes:

Russian knapweed (Centaurea repens) and yellow star-thistle (Centaurea solstitialis) are both naturalized in western Canada. Both plants cause chewing disease in horses. The problem is restricted to horses. Prolonged consumption of the plants is required to produce the symptoms. Russian knapweed is more toxic than yellow star-thistle (Cheeke and Schull 1985, Panter 1990):

- intake of 1.8-2.5 kg/100 kg of body weight per day of Russian knapweed causes toxicity after ingesting 59-71% of its body weight of the plant material in about 30 days;

 

- intake of 2.3-2.6 kg/100 kg of body weight per day of yellow star- thistle causes toxicity after ingesting 86-200% of its body weight of the plant material in about 54 days.

There are no known treatments for horses once the symptoms appear.

References:

Cheeke, P. R., Shull, L. R. 1985. Natural toxicants in feeds and poisonous plants. AVI Publishing Company, Inc., Westport, Conn., USA. 492 pp.

Cordy, D. R. 1978. Centaurea species and equine nigropallidal encephalomalacia. Pages 327-336 in Keeler, R. F., Van Kampen, K. R., James, L. F., eds. Effects of poisonous plants on livestock. Academic Press, New York, N.Y., USA. 600 pp.

Panter, K. E. 1990. Toxicity of knapweed in horses. Wash. State Univ. Knapweed, 4(3): 2.

Nomenclature:

 

Scientific Name: Centaurea repens L.

Vernacular name(s): Russian knapweed

Scientific family name: Compositae

Vernacular family name: composite

Go to ITIS*^ca for more taxonomic information on: Centaurea repens

References:

Agriculture Quebec. 1975. Noms des maladies des plantes du Canada/ Names of plant diseases in Canada. , Quebec City, Que., Canada. 288 pp.

Alex, J. F., Cayouette, R., Mulligan, G. A. 1980. Common and botanical names of weeds in Canada/Noms populaire et scientifiques des plantes nuisibles du Canada. Revised. Agric. Can. Publ., Ottawa, Ont., Canada. 132 pp.

Bailey, L. H., Bailey, E. Z. 1976. Hortus third. Revised. MacMillan, New York, N.Y., USA. 1290 pp.

Scoggan, H. J. 1978, 1979. The flora of Canada. Nat. Mus. Nat. Sci. (Ottawa) Publ. Bot. 7(1)-7(4). 1711 pp.

Van Wijk, H. L. 1911. A dictionary of plant names. Martinus Nijhoff, The Hague, The Netherlands. 1444 pp.

Victorin, M. 1964. Flore Laurentienne. 2nd ed. Univ. Montreal, Montreal, Que., Canada. 952 pp.

Geographic Information

 

Alberta
British Columbia
Manitoba
Ontario
Saskatchewan

References:

Bailey, L. H., Bailey, E. Z. 1976. Hortus third. Revised. MacMillan, New York, N.Y., USA. 1290 pp.

Boivin, B. 1966, 1967. Énumération des plantes du Canada. Provencheria 6. Nat. Can. (Que.) 93: 253-274; 371-437; 583-646; 989-1063. 94: 131-157; 471-528; 625-655.

Image or illustration

Russian knapweed:

 

Images: images.google.com

Notes on Poisonous plant parts:

Horses must ingest fresh aboveground plant material for prolonged periods to reach a threshold level of unknown toxicity and then the symptoms appear abruptly. Chewing disease in horses has occurred in parts of the western United States. In California the peak times of disease onset are June-July and October-November (Cordy 1978).

Toxic parts:

leaves
mature fruit
stems

References:

 

Cheeke, P. R., Shull, L. R. 1985. Natural toxicants in feeds and poisonous plants. AVI Publishing Company, Inc., Westport, Conn., USA. 492 pp.

Cordy, D. R. 1978. Centaurea species and equine nigropallidal encephalomalacia. Pages 327-336 in Keeler, R. F., Van Kampen, K. R., James, L. F., eds. Effects of poisonous plants on livestock. Academic Press, New York, N.Y., USA. 600 pp.

Mettler, F. A., Stern, G. M. 1963. Observations on the toxic effects of yellow star thistle. J. Neuropathol. & Exp. Neurol., 22: 164-169.

Toxic plant chemicals:

unknown chemical

References:

Cheeke, P. R., Shull, L. R. 1985. Natural toxicants in feeds and poisonous plants. AVI Publishing Company, Inc., Westport, Conn., USA. 492 pp.

Animals/Human Poisoning:

Note: When an animal is listed without additional information, the literature (as of 1993) contained no detailed explanation.

Horses

General symptoms of poisoning:

drowsiness
gait, unsteady
incoordination
restlessness

References:

Cheeke, P. R., Shull, L. R. 1985. Natural toxicants in feeds and poisonous plants. AVI Publishing Company, Inc., Westport, Conn., USA. 492 pp.