Scientific Name: Senecio jacobaea
Distribution: Principally on the West Coast and New England States, but starting to spread inland.
Type of Poison: Pyrrolizidine alkaloids
Signs of Poisoning: Signs may not appear until six months or more after the plant is eaten, and they may vary, depending on the amount of plant eaten and the rate at which it was eaten.
Growth Characteristics: A biennial forb with a somewhat bushy appearance, growing up to 5 feet tall. It is in the rosette stage the first year, and two flowering stems bolt the second year. It flowers in the fall. Tansy ragwort has a strong "weedy" odor.
Flowers/Inflorescence: Closely set clusters of yellow daisy-like flowers, each with 13 petals. It produces large amounts of seed.
Leaves: The rosette leaves are dark green and appear ruffled. The second year leaves have a parsley or carrot-like appearance, are alternate in arrangement, and attached to the stem without a petiole.
Tansy ragwort grows in areas with over 20 inches of rainfall annually; however, it could possibly grow in heavily irrigated locations with less rainfall. It infests woodlands, pastures, and hayfields. Tansy ragwort is rapidly spreading, which is of increasing concern to the livestock industry.
Tansy ragwort is generally unpalatable to livestock and therefore is eaten only when other food is scarce or when it cannot be avoided such as -- for example, when it is part of hay or silage and in lush pastures. It is toxic to all classes of livestock but most toxic to cattle and horses. The toxic alkaloids primarily affect the liver. Cells of the liver are slowly killed or prevented from reproducing and are gradually replaced by scar tissue. Whether an animal survives depends on the number of liver cells it loses, and the duration of survival depends on the rate at which it loses liver cells. Animals may survive for six months or longer after they have ingested a lethal amount of plant and may show no outward symptoms during this period. They may suddenly become lethargic, fill with fluid or edema in the abdominal cavity, and die within two to four days. They may also show central nervous system effects such as impaired vision and an incessant stumbling walk with no goal in mind. The onset of symptoms may be dependent on other stresses imposed on the liver, which it cannot handle in its weakened condition; thus, the true cause of death is often not ascertained. Cattle eating 5% or more of their total daily diet of pre-bloom tansy ragwort for periods exceeding 20 consecutive days can be expected to die within a six-month period.
When symptoms of poisoning appear, it is too late to save the animal; thus, the best preventative is avoidance of the plant. Young animals are more easily poisoned than mature animals. Pastures for horses and cattle with over 5% tansy ragwort content should be avoided until the tansy ragwort has been controlled. Hay and silage contaminated with tansy ragwort especially should be avoided as animals cannot sort out the tansy ragwort, as in a pasture situation.
Tansy ragwort can be controlled by cultivation. In other areas, research results show that tansy ragwort can be controlled with herbicides. It should be sprayed in the rosette stage. Consult with your local Cooperative Extension agent for specific types of herbicide and always follow precautions when handling herbicides.
L.F. James, R.F. Keeler, A.E. Johnson, M.C. Williams, E.H. Cronin, and J.D. Olsen. Plants Poisonous to Livestock in the Western States. U.S. Department of Agriculture, Agriculture Information Bulletin 415, 90 pp. 1980.
Washington State University, Kitsap County Extension “Tansy Ragwort: Senecio jacobaea” Web Page of Washington State University Kitsap County Noxious Weed Control - Dirty Dozen. 5 March 2012. http://county.wsu.edu/kitsap/nrs/noxious/Documents/TansyRagwort.pdf .