Tag Archives | Tansy ragwort


Tansy Ragwort Poisons Livestock and Neighborly Relationships!

Tansy ragwort has long tormented rural landowners who graze livestock. Horses and cows are especially susceptible to this poisonous weed. In open fields, grazing animals will generally avoid eating tansy ragwort, but in heavily infested pastures they may have few other options.  Contaminated hay is particularly a problem because it becomes impossible for feeding animals […]

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Tansy Ragwort (Senecio jacobaea)


Common names:

Tansy Ragwort, Stinking willie, Staggerwort, Tansy butterweed

Scientific Name:

Senecio jacobaea (syn. Jacobaea vulgaris)


Tansy ragwort is a tall biennial plant in the sunflower family. It can grow up to 6 feet in height at maturity. The rigid stems of Tansy ragwort are green with an occasional reddish tinge. Plants typically arise from a single stem that becomes branched at the top of the plant, forming flat clusters of bright yellow flowers. The yellow daisy-like flowers have dark yellow to orange centers. Leaves are dark green and ruffled in appearance. Tansy ragwort grows as a rosette in its first year before transitioning into the mature flowering form in its second year of growth. Tansy ragwort can form dense patches, particularly on disturbed sites. This noxious weed is dangerous to humans and livestock due to a poisonous alkaloid (hepatotoxic pyrrolizidine) in its tissue which causes liver damage when ingested.

Life cycle:


Height of mature plants

3-6 feet

Flower color:


Bloom time:

July to September


From a distance, tansy ragwort can look like common St. John’s wort (Hypericum perforatum), but upon looking more closely, tansy ragwort has large ruffled leaves, whereas St. John’s wort has many small leaves. Also, tansy ragwort has flowerheads with 13 petals, while St. John’s wort has 5.


Tansy ragwort is opportunistic plant often found in disturbed areas. Tansy likes a cool and wet climate, well drained soils and full to partial sun. Patches are found in pastures, fields, grasslands, vacant land, waste places, horse trails, roadsides, rangeland, riparian areas, forested areas, and clear cuts. Areas of greatest concern are improperly managed pastures and disturbed areas.


Prolific in pastures, clear cuts, and disturbed roadside areas, tansy populations can become quite dense. The leaves are toxic to cattle and horses, causing irreversible liver damage. In the 1960’s and 70’s livestock losses in Oregon amounted to 5 million dollars a year. Unlike cattle and horses, sheep appear to be unaffected by ragwort’s toxicity. Once considered Western Oregon’s most economically serious noxious weed, biological controls have reduced the severity of outbreaks below economic threshold levels.

Noxious Weed Listing:




Oregon Noxious Weed Profile
Washington Noxious Weed Profile
Invasive.org profile
CABI Invasive Species Compendium



A History of Invasive Weed Management in Clackamas County

A weed control headline, from the Oregon City Courier. (Oregon City, OR.), July 18, 1918

A weed control headline, from the Oregon City Courier. (Oregon City, OR.), July 18, 1918

Clackamas County has a deep seeded connection to Oregon agriculture.  Many of Oregon’s earliest agricultural enterprises began in Clackamas County.  Clackamas County hosts a number of the state’s oldest farms, and most famously was the site of Oregon’s first commercial nursery in present-day Milwaukie.  With this strong agricultural connection, weed management has been a historically important topic to Clackamas County residents.  Local farmers would share their tips and tricks, and new developments in weed management were important news of the day.  Many historic newspapers recount the importance of weed management to protect the viability of working farms in Clackamas County.

With the industrial revolution and the rise of urban centers within the county, the close connection that residents had with the land began to diminish.  The livelihoods of residents were not as closely tied to the quality of the land.  As a result, invasive weeds became more and more commonplace.  The rampant onslaught of invasive weeds rose to the forefront in the late 1940s, with the prolific spread of Tansy ragwort (Senecio jacobaea).  The poisonous qualities of tansy ragwort and the subsequent poisonings of horses and livestock proved to be a wake-up call for the need for more active management within the county.

Tansy Ragwort Inspection

County Agent, Ron Davis, looks at a field of tansy, Clackamas County, ca. 1946

In 1949, Clackamas County formed a noxious weed control board to address the rampant spread of tansy ragwort.  At that time landowners could be fined for having noxious weeds growing on their property.  Neighbors began working together to control invasive weeds and community weed pulling events sprouted up throughout the county to combat invasive weeds.

With the introduction of biological controls beginning in the 1960s and 1970s, the threat from tansy ragwort and other invasive weeds were dramatically reduced from peak historic abundance.  The continued urbanization of Clackamas County and the relative success of biological controls challenged the importance of noxious weed control.  With severe budget constraints in the 1980s, Clackamas County disbanded their noxious weed control board in 1989.

Weed control district dissolution headline, from the Oregon City Enterprise-Courier. (Oregon City, OR.), August 5, 1989

The weed control district dissolution headline, from the Oregon City Enterprise-Courier. (Oregon City, OR.), August 5, 1989

With the dissolution of the Noxious Weed Control Board enforcement of noxious weed laws effectively ended at the county level.  As such a vacuum was created regarding invasive weed control and management.  In the mid-1990s, the Clackamas Soil and Water Conservation District worked with various public partners to address the ongoing need for technical assistance related to invasive weeds.  They partnered with the Oregon Department of Agriculture, Oregon State University Extension Service, the Soil Conservation Service, and Clackamas County to form a non-regulatory Weed Advisory Board in 1994.  Upon creation, the Weed Advisory Board spearheaded an ongoing effort to combat gorse within the county, but ongoing funding constraints slowly diminished activities. By the late 1990s, all activities associated with the Weed Advisory Board had ceased.

In November 2006, the Clackamas Soil and Water Conservation District sought and received a permanent tax base within Clackamas County.   One of the primary components outlined in ballot measure 3-221 was to respond “to citizen demands to implement a countywide weed program focused on education and sustainable control methods.

Upon receiving their permanent tax base the Clackamas Soil and Water Conservation District formed a Weed Task Force which in 2008 develop a framework for the new weed program.  In early 2009, the Clackamas Soil and Water Conservation District hired a full-time program manager to develop and administer the “WeedWise Program”  to support more effective management of invasive weeds in Clackamas County.

Since inception, the WeedWise Program has focused on preserving the social, economic, and ecological resources within Clackamas County.  Primary efforts of the WeedWise program are to serve as a technical resource to local landowners and land managers trying to control invasive weeds on their property.  The program also has a strong focus on promoting public awareness and education on the impacts of invasive weeds in Clackamas County.

In 2010, the WeedWise program was able to launch an Early Detection and Rapid Response initiative to target priority invasive weeds in Clackamas County.  This initiative focuses on preventing the introduction of new damaging weeds, while systematically working to reduce the expansion of existing invasive weeds.  Since that time, hundreds of thousands of dollars have been invested in the control of invasive weeds in Clackamas County.

The WeedWise program continues to grow and develop and has steadily expanded its efforts within the county.   The program was able to hire additional staff in 2011 and 2014 to support priority invasive weed control efforts and is working hard to meet the growing demand for services within Clackamas County.  As the WeedWise program continues to grow and develop, it will continue to build upon the efforts of its predecessors to promote effective invasive weed management to preserve the livability of Clackamas County.

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