Tansy ragwort

(Senecio jacobaea)

 

Invasive implications

Tansy ragwort emerged as a threat to the Pacific Coast in the mid 1850s, making its way from California after being introduced to North America. This biennial weed is native to Europe, Asia, and Siberia, thriving in cool, wet coastal habitats. Tansy ragwort is considered to be a noxious weed by many authorities because it can dominate pastures, compete with desirable vegetation, and poison livestock with its harmful alkaloids. These alkaloids are concentrated in flowers and can cause liver damage to cattle, horses, deer, and pigs, leading to death with persistent exposure (see links below). Sheep appear to be less affected as they can daily graze on young tansy ragwort plants without suffering any ill effects. Tansy ragwort alkaloids also reduce butterfat production in cattle and taint the honey collected from foraging bees (there are growing concerns for human consumption of these products). Due to these invasive characteristics, control efforts have ensued for over fifty years. These efforts are hampered with the pervasiveness of Tansy ragwort due to its persistent seed bank, vegetative reproductive success, and its ability to resist introduced biological agents.

 

Identification

Spring

Summer

Winter
 

 

  •  emerge as low, dense, rosette
  •  may obtain heights of 1.75m
  •  grows as an erect biennial or short-lived perennial

  •  rosette begins to form

 
  •  old rigid stalk can persist throughout winter

Leaves

Stem/Roots

Flower/Fruit
 

 

 
  •  alternate, reducing in size up the plant
  •  lower leaves are 7 to 20 cm long and 2 to 6 cm wide
  •  have a "ragged" appearance due to deep, irregular cuts
  •  upper stem is multi-branched
  •  multiple fleshy roots grow to a depth of 30cm
  •  poorly developed to evident tap root
  •  20-60 ray-type flowers, 13 petals
  •  bright golden in late July and August
  •  head of flower: 7-10mm, petals: 8-12mm in length
  •  seed germination occurs in the late summer or autumn with rosettes developing the following winter/spring

 

Similar Plants

Common tansy (Tanacetum vulgare)

Tansy ragwort can be confused with other Senecio cousins by its larger size, unique dissected leaf structure, and ray-type flowers. Common tansy does not have ray flowers and has leaves which are sharply toothed.

 

    Key Features

Tansy grows on disturbed sites in pastures, waste places, roadsides and clear-cuts. It prefers areas with cool, wet, cloudy weather and is therefore common in coastal climates. Optimal growth occurs in light, well-drained soils; Tansy ragwort is usually absent in areas with high water tables or acidic soils. As mentioned, this weed is a biennial (lives for two years) but is reported to persist as a perennial in some cases. It can be found as either a rosette or seed over winter.

Flowering usually occurs during the second year with seed dispersal throughout the fall. Some plants may regenerate after flowering, especially in response to disturbance. Seeds are pollinated by a variety of insect types and are said to have high viability - up to 16 years. Each plant can produce from 55,000 - 175,000 seeds, depending on environmental conditions. They are dispersed via livestock, water, bird droppings, and to a lesser extent by wind. Tansy ragwort also propagates vegetatively, regenerating its shoots from crown buds, dug up root fragments, and from intact roots. Disturbance or injury promotes this type of propagation.

Interestingly enough, Tansy ragwort was extensively prescribed in medieval medicine to help aches and pains in arms, hips, and legs - boiled in hog's grease to the form of an ointment. It was also used to treat coughs, colds, ulcers, sores and wounds. Please note that these medical remedies are not recommended for current day use.

 

Control Measures

The success of S. jacobaea is clearly attributed to its toxic alkaloids and reproductive abilities, which enable this weed to invade and survive in pastureland. Accordingly, S. jacobaea is listed as a prohibited noxious weed in the Canada Seeds Act and as a Class 1 noxious weed in the Weed Control Act of B.C. This weed is a real nuisance for B.C. farming communities where it reduces forage production of pastures by up to 50%. Most farming animals do not directly graze ragwort but the poison from this weed can persist in silage, deeming crops unusable.

Control attempts using strictly mechanical methods or herbicides rarely produce effective long-term results. However, Tansy ragwort can be managed through a combination of biological, physical and chemical controls. In B.C., several biological agents have been introduced including two moths, two beetles, and one fly (see biological control). Of these, a combination of Longitarsus jacobaeae and Cochylis atricapitana are successfully controlling localized areas. Sheep grazing is another effective control option as sheep do not suffer ill effects from this plant's toxic alkaloids. Hand pulling and cultivating techniques are useful in smaller areas, where care can be taken to remove the entire root system.

 

Non Chemical Control
  Hand pulling Mechanical Removal Mulch
How Remove the entire stem and root system using hand or digging tool Use machinery to completely uproot or frequently cultivate plants Surround desirable plants with straw or other suitable mulching material at least 0.3m deep, extending 4.6m beyond perimeter of patch
When Pull plant when soils are moist to ensure complete root system is removed June and July, before ragwort sets seed. Remove plants first and cover all year round
Duration

 

 Until plant is eradicated from the area Should only be performed once to minimize soil disturbance. At least three years to kill the root systems of the plants
Pros/Cons Hand pulling is only effective where there are a few plants in their first year of growth Tansy thrives in soil disturbance and recovers well from mowing. This is an effective yet costly and labour intensive form of control

 

Non Chemical Control
  Burning Grazing
How Flame throwers or weed burners can be used as spot treatments to heat girdle small patches of tansy ragwort seedlings Tansy is deemed a good summer feed for sheep.
When Any time of year, preferably when fire hazards are low Before plant flowers and sets seed (in early summer). May be more effective in rosette stage but no studies on this to date. Grazing is not recommended in early fall or later in the year as this may stimulate plants to develop multiple crowns.
Duration

 

 No information - but should eradicate small stands after one or two seasonal treatments. Intense grazing for 2 to 3 years in sequence will reduce tansy ragwort populations so that cattle could be grazed safely during the growing season
Pros/Cons Very effective in killing reproductive plants and destroying the viability of the attached seed Intensive grazing is the primary means of control in New Zealand.

 

 

Chemical Control

Biological Control
 

Spot Application

Insects
How Young seedlings and rosettes be controlled using applications of 2,4-D, dicamba or a combination of both. See BC Ministry of Agriculture Longitarsus flavicornis (beetle), Botanophila seneciella (fly), Tyria jacobaeae (cinnabar moth), Cochylis atricapitana (moth), Longitarsus jacobaeae (beetle) have all been introduced in B.C. These insects/larvae feed on various parts of tansy such as foliage, leaves, and stems.
When Applying in early spring or mid-fall when active new growth is occurring is effective. Refrain from cutting or foraging hay for 7 days following application First biological agent was released in 1962 in British Columbia. There are opportunities for volunteers to participate in release of these control agents. See BC Ministry of Agriculture
Duration Repeated treatments (spring and fall) are recommended for optimum control Like other biological control methods, this technique does not have an endpoint.
Pros/Cons Can cause damage to clover; livestock should be excluded from pasture for at least 3-4 weeks Although this technique does not eradicate weeds, several agents have proved to be successful in reducing overall densities of Tansy ragwort. Can take 5-10 years to establish but provides inexpensive, long-term, and non-toxic control

 

Control Warnings:

Disposal - Make sure to properly discard all plant pieces in thick plastic bags and transport them to a sanitary landfill site or incinerator. Composting is not an appropriate means of disposal as this may result in further distribution. Remember that humans can actually spread invasive plants by taking seeds from one place to another on clothing, tires, equipment, etc.

Chemicals - Although some chemicals are approved for control of invasive plants, extreme caution must be taken as many pesticides are harmful to humans. Permits may be required for chemical use and buffer zones exist beside waterways to protect fish and wildlife. Chemical control is not a long-term solution and therefore should be part of a finite plan and applied sparingly. Please see the following web sites for further information: Provincial: MWLAP Pest Information  Federal: Pest Management Regulatory Agency

Biological - Extreme caution must be taken when introducing one organism to control another. Intensive testing must occur before initiating a safe and effective biological control agent. Please contact local government or environmental agencies to determine available volunteer opportunities.

 

Additional Resources