Habitat, Spread and Impacts

Habitat

Tansy ragwort tolerates a wide range of habitats and environmental conditions but is generally found on mesic sites with cool, wet, cloudy weather. It grows on many soil types but usually on lighter, well-drained loamy or sandy soils. It normally does not grow where there is a high water table or on soil with high acidity. In Europe it naturally occurs in sand dune, woodland, and grassland communities. In North America it is found in pastures, forest clearings, and waste places and is often associated with Canada thistle (Cirsium arvense), common St. Johnswort (Hypericum perforatum), and yellow toadflax (Linaria vulgaris).

Spread

The pappus on the achene of tansy ragwort facilitates wind dispersal. However, achenes are generally considered to be poor wind dispersers and studies suggest 60 percent (%) of tansy ragwort seeds fall within seven feet (2 meters) of the parent plant with only 0.5% of seeds produced actually becoming wind borne. One dispersal study found that all achenes fell within 46 feet (14 meters) of the parent plants. Seeds can also disperse by water movement, through the digestive tract and adhering to livestock and other animals, and viable seeds have been collected from bird droppings. Original infestations in North America are believed to have arrived in soil used as ship’s ballast. Tillage equipment used in fields where tansy ragwort occurs can spread root and caudex fragments within the field and to fields where the equipment is subsequently used. In Montana, tansy ragwort has established on logging sites and clearings, implicating equipment used for logging as a long-distance spread vector. The showy flowers may encourage people to transplant or seed tansy ragwort into gardens from which it can spread to pastures and native plant sites.

Impacts

Tansy ragwort can reduce forage yields by as much as 50% in pastures. Pyrrolizidine alkaloids are present in all plant parts. Cattle, deer, horses and goats consuming either growing plants or tansy ragwort in silage and hay store these alkaloids in their livers. Even if symptoms are not evident or are minor in nature, the cumulative storage of alkaloids can result in reduced weight gain, liver degradation, reduced butterfat content of cow’s milk, and sudden death in apparently healthy animals. Alkaloids in tansy ragwort pollen also taint honey, making it bitter, off-color and unmarketable.

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Last Modified: 06/18/2009