Tansy Ragwort in British Columbia

Tansy Ragwort in British Columbia

Tansy ragwort (Senecio jacobeae) is a poisonous plant causing environmental deterioration, loss of pasture for grazing animals and even unthriftiness and death to livestock in the Lower Fraser Valley and southern Vancouver Island. Native to the British Isles and likely introduced to North America as a medicinal herb, tansy ragwort has invaded pastures, woodlands and waste areas from Hope, B.C. south throughout the Fraser Valley and north on Vancouver Island to Nanaimo. It was first recorded in B.C. at Nanaimo in 1950 (Royal Provincial Museum).

Good pasture management combined with effective biological control and public awareness will reduce spread and the negative impacts of this weed.

The Plant

Tansy ragwort is a biennial to short-lived perennial plant in the Sunflower family. A low-growing rosette of leaves is produced in the first year. Erect stems growing 0.3 to 1.2 metres (1 to 4 feet) high are produced in the second and often subsequent years. The dark green stalkless leaves are deeply cut into irregular segments giving the plant a “ragged” appearance. The daisy-like bright yellow flowers, evident from July through September, produce an abundance of seed which is easily transported by wind, water and animals. One ragwort plant can produce in excess of 150,000 seeds. Seeds can lie dormant on the soil surface for 4 to 5 years or over 20 years if buried. Seeds germinate in both spring and fall to form new rosettes.

People often confuse tansy ragwort with common tansy (Tanacetum vulgare). Common tansy however does not have ray flowers, and has leaves which are sharply toothed.

common tansy image

Common Tansy (Note: Has no ray flowers and leaves are sharply toothed) Tansy Ragwort (Note: Conspicuous ray flowers and deeply lobed leaves

Pastures and Livestock Suffer

Tansy ragwort invasion of your pasture (irrigated and non-irrigated) and woodlands can reduce forage available to grazing animals by fifty percent or more. This poisonous weed is not a preferred forage and animals will usually try to avoid it in a pasture if more desirable forage is available. Poisonings most often occur as a result of feeding contaminated hay or silage or in spring pastures when young rosettes cannot be selectively avoided as grass and clovers are grazed.

rosette image Tansy ragwort rosette with extensive root system results in strong competition with beneficial pasture plants

pasture image Pasture densely infested with tansy ragwort

Stock Poisoning

Tansy ragwort contains at least six pyrrolizidine alkaloids which by themselves are not toxic. When combined with liver enzymes after ingestion they are converted to pyrroles which result in liver dysfunction and sometimes death. Cattle and horses are most seriously affected followed by goats. Sheep are not as easily impacted by this weed and in fact are used in some countries as a form of biological control. Cattle can be poisoned by consuming only 2 to 8 percent of their body weight. Young animals are more susceptible to poisoning than mature animals. Avoid grazing horses and cattle on pastures with over 5 percent tansy ragwort until the plants are controlled.

Symptoms

Most poisonings of cattle and horses are caused by eating small amounts over an extended period of time. Poisoning is cumulative and will result in liver dysfunction even after animals have been denied access to ragwort. Symptoms include depression, loss of appetite, chewing of fences and dirt, restlessness and wandering aimlessly, walking into fixed objects, 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 from liver damage.

Human Cautions

Flowers of tansy ragwort contain the highest percentage of the toxin. This raises concern as the alkaloids have been found in dilute form in honey made from bees foraging in areas of high ragwort concentration. Alkaloids are passed into the milk of cows and goats as well but the potential for human poisoning appears very slight. Nevertheless, long term consumption of trace amounts of the alkaloids in milk or honey should be observed with caution. You should limit animal access to ragwort plants to prevent toxin entry to the food chain.

How To Reduce Losses

Poor management practices lead to a decline in the competitive ability of preferred forages and a build-up of tansy ragwort populations.

Beginning a program of integrated pasture management will prevent future livestock losses from this weed. The following three control factors are essential components of a successful long term solution to the problem:

1. Prevention:

Don’t let ragwort go to seed. Hand pull isolated plants and small patches and remove as much of the root as possible. In heavy infestations you must mow often and thoroughly to do any good. Plants mowed after flowering begins can still produce seed.

Maintain a healthy competitive forage stand by:

seeding to adapted forage grasses and legumes;
fertilizing according to soil needs as indicated by soil test;
grazing pastures uniformly and not excessively. Over stocking for the forage present is the leading cause of pasture deterioration and resultant weed invasion;
reseeding any soil disturbances such as rodent push-ups, hoof marks, vehicle tracks, etc. Ragwort quickly establishes where soil is exposed or forage is in a weakened condition.

2. Chemical Control

Tansy ragwort is easily controlled in the seedling to young rosette stage with the herbicide 2,4-D as either the amine or low-volatile ester formulation. Applying in early spring or mid-fall when active new growth is occurring is effective. Clovers can be severely damaged by 2,4-D but often recover. When rosettes are large or in more advanced growth stages such as flower stalk elongation the herbicide dicamba (Banvel) or dicamba plus 2,4-D provides excellent control. Do not graze or cut forage for hay for 7 days following application of Banvel at the recommended rate of 2.1 L/ha. Use Banvel only where loss of the clover component of the forage can be tolerated. Remove animals from 2,4-D treated pastures for 7-10 days as this herbicide can increase the palatability of poisonous plants.

USE CAUTION WHEN USING HERBICIDES AND READ THE LABEL BEFORE USE.

3. Biological Control

Cinnabar moth larvae
defoliating mature tansy ragwort.

Insect agents that attack the seedhead, roots and leaves of ragwort make the weed less competitive and reduce seed production. These insects are introduced from the weed's native habitat after exhaustive studies to ensure they will attack only the target weed. Agriculture Canada introduced the first of three insects imported to attack tansy ragwort in 1962. This agent, the cinnabar moth (Tyria jacobaeae), is characterized by black and yellow larvae (caterpillars) about one inch long. The adult stage is a distinctive black and red moth. Larvae feed on the flowers and young foliage, often stripping the entire plant including tender stems. Localized defoliation does occur but results have proven less than dramatic in B.C. Damaged plants are normally able to overcome the attack and buildup sufficient root food reserves to prevent winter damage. A seed head fly (Hylemya seneciella), also established in B.C., is causing minor seed reductions. The most promising of the agents in the ragwort biocontrol arsenal is the ragwort flea beetle (Longitarsus jacobaeae). Small tan coloured beetles lay eggs on ragwort rosettes in the outside bark of both lateral and central roots, producing long scarred grooves. They may also mine the center of the main root. Adult feeding on rosette leaves give the leaves a “shot-hole” appearance. The beetles, combined with good pasture management have successfully controlled ragwort in parts of California and Oregon. Intensive mowing to reduce seed production will not interfere with the beetles.

The Ministry of Agriculture and Food is actively involved in collecting and redistributing the flea beetle throughout the weed's B.C. range. Contact your local Ministry office if you would like to participate in the beetle release program.

Success of current biocontrol efforts is limited to reducing competitiveness of ragwort rather than a major reduction in weed density. New agents will be released once approved which will place further stress on the weeds.

moth image Adult cinnabar moth are most active during June and July

beetle image Tansy ragwort flea beetle and "shot hole" feeding on rosette leaf.

larve image Tansy ragwort flea beetle and "shot hole" feeding on rosette leaf.

Long Term Solution

The long term solution to tansy ragwort control will be a combination of:

good pasture management
judicious herbicide use
effective biocontrol
a high level of public awareness

What Can You Do?

PREVENT SPREAD BY SEED PRODUCTION.
BE AWARE. Learn to recognize tansy ragwort.
PRACTICE INTEGRATED PASTURE MANAGEMENT by using all methods at your disposal to increase competitiveness of desirable forage vegetation.

Co-published by:
The B.C. Ministry of Agriculture and Food
Central Fraser Valley Regional District

Tansy Ragwort Abatement Program
Central Fraser Valley Regional District
34194 Marshall Road, Abbotsford, B.C.
Phone: 853-1368

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