Russian knapweed-Centaurea repens L.-Poisonous plant

Russian knapweed

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.

Description

Russian Knapweed is a creeping perennial weed, native to Eurasia, which reproduces by seed and underground rhizomes. It resembles the common garden bachelor button, of which it is a relative. The roots are extremely vigorous, spreading, extensive, and characteristically black in color. The stems are erect, 2-3 feet tall, branched at the base, ridged, and have a dense gray hair-like covering. Leaves of three shapes are found on the plant. The lower leaves are pubescent. The upper leaves are small, linear, with smooth edges. Intermediate leaves have slightly toothed margins. The leaves are pubescent. The numerous rose to purple flowers are about ½ inch wide and shaped like a flask. Flowers bloom in July and seeds are formed from July to September.

Nomenclature:

Scientific Name: Centaurea repens L.

Vernacular name(s): Russian knapweed

Scientific family name: Asteraceae

Vernacular family name: Asteraceae

Geographic Information

Alberta, British Columbia, Manitoba, Ontario, Saskatchewan.

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.

Toxic plant chemicals:

Unknown chemical.

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.