Tansy ragwort

Identification & Biology
Alias' : tansy butterweed, stinking Willie
Latin Name : Senecio jacobaea
Category : Terrestrial Plants
Description :
  • Biennial or short lived perennial
  • Grows 0.3 to 1.2 metres tall
  • One to several erect stems
  • Leaves are deeply cut into irregular segments, giving the plant a ‘ragged’ appearance
  • Yellow ray flowers grow in a flat-topped cluster


Typically, rosettes are formed in the first year, followed by bolting of a single flowering stalk in the second year. Flowering occurs from July through September, depending on geographic location. Tansy ragwort reproduces by seed. Seeds may germinate in both the spring and fall, forming new rosettes. A single tansy plant can produces more than 150,000 seeds, which may remain dormant for 4 to 5 years, and are viable for over 20 years. Seeds are primarily dispersed through wind and water and wildlife and human activities. Plants may also regenerate vegetatively when damaged.

Tansy ragwort is often confused with common tansy (Tanacetum vulgare). Common tansy lacks ray flowers, and its leaves are sharply toothed compared to tansy ragwort.

Look Alikes

In British Columbia, tansy ragwort occurs throughout the coastal regions on Vancouver Island, some of the southern Gulf Islands and the Fraser Valley. It is primarily considered a coastal species; however, the largest provincial infestation occurs in the Chute Lake area of the Okanagan Valley. This isolated infestation is currently one of only two known occurrences of tansy ragwort in BC’s Interior; another small outbreak occurs near Crystal Mountain near West Kelowna. Tansy ragwort prefers disturbed area of pastures, hayfields, roadsides and clear-cuts.

Impact & Risks
  • Tansy ragwort can reduce forage production in pastures by as much as 50%, due to competition and plant toxicity.  
  • The entire plant contains varying concentrations of poisonous alkaloids, which cause irreversible liver damage in wildlife and livestock. Animals often avoid grazing plants; however, they are unable to detect tansy presence when mixed into hay or silage. Animals may select tansy in overgrazed pastures; where better forage is limited.  
  • Poisoned animals may experience depression, loss of appetite, restlessness or a yellow or muddy discolouration of mucous membranes and an unpleasant pig-like skin odour. In severe cases, serum will seep through the skin due to a photosensitive reaction resulting in liver damage. 
Prevention & Mitigation

The most effective way to ensure that your lands do not become infested with tansy ragwort is by prevention. Here are some recommendations to prevent invasion on your property:  

  • Maintain your crops and natural lands in a healthy, vigorous condition to ensure a competitive plant community; competitive perennial grasses and forbs utilize water and nutrients that would otherwise be readily available to ragwort. 
  • Follow a well-designed grazing management plan; excessive livestock grazing reduces competition and favours invasive plants. 
  • Regularly patrol your property for tansy ragwort plants and immediately control or remove infestations before seed set. 
  • Cooperate with adjacent landowners and encourage them to prevent tansy ragwort spread. 
  • Immediately re-vegetate disturbed, bare soils with a suitable seed mixture that provides dense, early colonization to prevent weed invasion. 
  • Clean your vehicles and machinery of plant material and soil before leaving a ragwort infestation, or any other invasive plant infestation. 
  • Do not move contaminated soil to a new area.  
Treatment & Disposal
  • Mowing may be utilized to prevent seed production. Plants should be cut just before flowering. Repeated mowing appears to increase rosette density.  
  • Hand pulling is an effective method, especially if it is done when soils are moist and the hole left after pulling is mulched.  
  • Mulching creates unsuitable habitat for ragwort germination by removing necessary light.  
  • Pulling is recommended for small patches or a follow-up measure after a population has been brought under control.  
  • If plants are hand-pulled or cut post flowering, all plant parts, including flower heads, should be bagged and incinerated or buried deeply at the landfill. 
  • Chemical control is also an option. Before applying herbicides, read the label for full use and precautionary instructions.  
  • For further information on the selection and application of chemicals to protect your crop, contact AgriService BC at 1-888-221-7141 or email AgriServiceBC@gov.bc.ca. 
  • In the Fraser Valley and coastal regions of BC, a defoliating moth (Tyria jacobaeae), seedhead fly (Hylemya seneciella also known as Botanophila seneciella), root feeding beetles (Longitarsis flavicorni, Longitarsis jacobaeae), and root crown feeding moth (Cochylis atricapitana) have been effective biocontrol agents for tansy ragwort. In the Okanagan valley, above Naramata, a summer breeding strain of L. jacobaeae is now well established and effectively suppressing the tansy ragwort population.
Okanagan Distribution

Priority Level Definitions

Watch For - Poses a significant threat (very high risk) and does NOT presently occur in the region OR is relatively new to the region and is very limited in extent.
High - High risk/impact; limited population with significant potential to spread in the region.
Medium - Medium risk/impact; limited distribution – broader population distribution with potential to spread further in a region.
Low - Low risk/impact; may be widespread or not, may be of concern in specific situations with certain high values – e.g. specific agriculture crops. Some species may be treated primarily with biological control agents.