Tansy ragwort (Senecio jacobaea) is a winter annual, biennial, or short-lived perennial plant in the sunflower family. The plant was unintentionally introduced into Canada about 1850, occurred in the state of Washington by 1901 (Rice 2015), and is currently reported in 14 states and four Canadian provinces (Figure 1). The plant is classified as a noxious weed in seven western states (AZ, OR, WA, CA, MT, CO and ID), two eastern states (CT and MA), and Canadian provinces. Tansy ragwort spreads mainly in hay, or on contaminated equipment and vehicles. The invasive plant is well suited to disturbed sites such as roadsides, open forests, logged areas, burned sites, and over-grazed meadows and pastures.
Identification and Spread
Tansy ragwort can reach more than four feet in height. The plant usually grows as a biennial, but can remain in a rosette stage for several years before bolting and producing seed. Mechanical damage to tansy ragwort such as mowing can also cause the plant to persist more than two years. The plant has a basal rosette of leaves, and the upper parts are branched. Leaves are deeply pinnately dissected into irregular segments giving the plant a ragged appearance. Yellow daisy-like flower heads with golden to light brown centers form at the tip of each branch from mid-summer to fall. Tansy ragwort spreads primarily by seed, which are dispersed within about 30 feet of the parent plant. Seed can remain viable for more than 10 years. Tansy ragwort can also reproduce from crown buds under environmental or mechanical stress (Figures 2 and 3).
Tansy ragwort can reduce desirable forage production by as much as 50 percent in meadows and pastures. The invasive plant is poisonous to some types of livestock and wildlife including cattle, deer, horses and goats. Sheep are able to consume the plant without harmful effects. Tansy ragwort contains pyrrolizidine alkaloids, which primarily affect the liver. In susceptible animals, liver cells are slowly killed and prevented from regenerating. The poisonous pyrrolizidine alkaloids are present in actively growing plants, and in plants that are cut, dry and in hay or silage. Reduced weight gain, liver degradation, lower butterfat content in milk and sudden death of an animal can be caused by ingesting tansy ragwort. When symptoms of tansy ragwort poisoning appear, it is too late to save the animal; thus, the best prevention measure is to removal the plant from pastures. Alkaloids in tansy ragwort pollen also taint honey, making it bitter, off-color and unmarketable.
Tansy ragwort can be effectively controlled using selective broadleaf herbicides. Field studies conducted on tansy ragwort show that Milestone® herbicide at 4 to 7 fluid ounces per acre (fl oz/A) or Transline® herbicide at 1 pint per acre (pt/A) provided good to excellent control one year following application (Figure 4). Results from operational control programs in northwestern Montana and northeastern Idaho support the application of Milestone at 5 or 7 fl oz/A for tansy ragwort control (Williams and Martinson personal communication).
The optimum time to apply herbicides to control tansy ragwort plants and stop seed production is at rosette to early bolt stage in spring, or to fall rosettes.
Tansy ragwort is often difficult to locate until the plant blooms; thus, treatments continue through summer months into fall in some operational programs. Clipping, bagging and removing flower heads from the infested site may be necessary to stop seed production at mid- to late-flower growth stage. Tansy ragwort rosettes and seedlings that are growing in association with mature plants will be controlled with Milestone, and residual properties of the herbicide will stop seedling establishment during the fall.
Managing grazing livestock to support a vigorous desirable plant community is recommended to prevent tansy ragwort invasion into new pastures or re-invasion in previously infested pastures. Sheep are immune to the plant’s toxic alkaloids and willingly graze young plants. In New Zealand, intensive sheep grazing is utilized to manage tansy ragwort. Tansy ragwort is poisonous to cattle, horses and goats. To prevent death of susceptible livestock, tansy ragwort density must be less than one plant per square yard and occupy not more than 25 percent of a pasture.
Three insects, including the cinnabar moth (Tyria jacobaeae), tansy ragwort seed fly (Botanophila seneciella) and the tansy ragwort flea beetle (Longitarsus jacobaeae) were introduced from 1960 to1971 in western Oregon and California to control tansy ragwort. Since that time insects have also established on tansy ragwort infested sites in Oregon, Washington, northern Idaho and northwestern Montana.
The ragwort flea beetles introduced to the United States before 2002 were collected in Italy and are credited with control and suppression of tansy ragwort infestations west of the Cascades. A Swiss strain of this agent with a different phenology than the Italian strain is believed to be better adapted to higher elevations, colder winters and shorter growing seasons typical of tansy ragwort infested areas east of the Cascades.
The insects have successfully reduced tansy ragwort populations throughout the Pacific Northwest. In Oregon, cattle deaths were reduced by more than 90 percent as a result of wide-spread insect establishment. Fluctuations in tansy ragwort populations can occur over time based on environmental conditions that favor either the insect or tansy ragwort growth.
OTHER CONTROL METHODS
Hand digging that removes the entire root crown and upper portion of roots will effectively control individual plants and very small infestations. Wearing protective gloves when handling tansy ragwort is recommended as a precautionary measure. Mowing is not effective and may cause the plant to develop perennial characteristics.
Maintaining a desirable competitive plant community is critical to stop reinvasion of tansy ragwort. Shading and competition for light, moisture, and nutrients will make survival difficult for tansy ragwort seedlings.
Bain JF. 1991. The biology of Canadian weeds. 96. Senecio jacobaea L. Canadian Journal of Plant Science 71: 127-140.
Coombs E, Hulting A, Pirelli G, Filley S. 2011. Tansy Ragwort. Oregon Department of Agriculture and Oregon State University Extension. [online] Available http://extension.oregonstate.edu/douglas/sites/default/files/documents/tragwortupdate2011.pdf
Jacobs J. 2009. Plant Guide for tansy ragwort (Senecio jacobaea L). USDA-Natural Resources Conservation Service, State Office, Bozeman, MT 59715. [online] http://plants.usda.gov/plantguide/pdf/pg_seja.pdf
Littlefield JL, GP Markin, KP Puliafico, AE deMeij. 2008. The release and establishment of the tansy ragwort flea beetle in the northern Rocky Mountains of Montana. XII International Symposium on Biological Control of Weeds. [online] Available http://www.invasive.org/proceedings/pdfs/12_573-576.pdf
Markin GL and JL Littlefield. 2008. Biological control of tansy ragwort (Senecio jacobaeae, L.) by the cinnabar moth, Tyria jacobaeae (CL) (Lepidoptera: Arctiidae), in the northern Rocky Mountains. XII International Symposium on Biological Control of Weeds. [online] Available http://bugwoodcloud.org/ibiocontrol/proceedings/pdf/12_583-588.pdf
Martinson, Alan. Latah County Idaho. Personal communication.
McGrew, Brian. Arizona Department of Agriculture. Personal Communication Feb. 2016.
Rice PM. 2015. INVADERS Database System (http://invader.dbs.umt.edu). Division of Biological Sciences, University of Montana, Missoula, MT 59812-4824.
USDA ARS. 2006. Tansy Ragwort (Senecio jacobaea). [online] Available http://www.ars.usda.gov/Research/docs.htm?docid=9988
USDA, NRCS. 2015. The PLANTS Database (http://plants.usda.gov, 2 December 2015). National Plant Data Team, Greensboro, NC 27401-4901 USA.
Williams, Dan. Lincoln County, Montana. Personal communication.
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Active ingredients for herbicide products mentioned in this article: Milestone (aminopyralid), Transline (clopyralid).
Published September 2016; reviewed and updated June 2019