Tansy ragwort [Senecio jacobaea L.][SENJA][CalEPPC: B][CDFA list: B] Photographs Map of Distribution

Common groundsel [Senecio vulgaris L.][SENVU] Photographs

Oxford ragwort [Senecio squalidus L.][Bayer code: none][CDFA list: B] Photographs Map of Distribution

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GENERAL DESCRIPTION:Yellow-flowered herbaceous plants with alternate, pinnately lobed leaves. Many Senecio species contain pyrrolizidine alkaloids toxic to humans and livestock when ingested in a single large quantity or in small amounts over time. Cattle, horses, goats, and young animals are more susceptible to poisoning than sheep. Introduced from Eurasia.

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SEEDLINGS:Remain as rosettes until maturity. First leaves alternate. Subsequent leaves variable, margins toothed to deeply pinnate-lobed.

MATURE PLANT:Foliage glabrous to lightly covered with long wavy to cottony hairs, especially along midveins and on lower leaf surfaces and new growth. Leaves highly variable, +/- evenly spaced on stems. Lower leaves taper into indistinct petioles. Upper leaves reduced, sessile, +/- clasp stem.


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FLOWERS:Flower heads yellow, clustered at stem tips. Phyllaries (flower head bracts) often black-tipped, in 1 equal row, typically with a few highly reduced phyllaries at the base. Insect-pollinated.

FRUITS and SEEDS:Achenes cylindric with shallow ribs, 1.5-3 mm long, light brown, often pubescent. Pappus bristles numerous, soft, white, about twice the achene length. Pappus +/- deciduous.

POSTSENESCENCE CHARACTERISTICS:Dead brown stems can persist for several months.

HABITAT:Disturbed sites, waste places, roadsides.

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PROPAGATION/PHENOLOGY:Seeds (achenes) disperse with wind, water, agricultural machinery, and by clinging to fur, feathers, and feet of animals and shoes and clothing of people.


SIMILAR SPECIES:Woodland groundsel [Senecio sylvaticus L.][SENSI] is an introduced European annual of open, disturbed woodland and rocky areas along the Central and North Coast. It resembles common groundsel, but unlike common groundsel, woodland groundsel lacks or has a few inconspicuous reduced phyllaries with green tips. In addition, it has a few (< 8) ray flowers with corollas that barely extend beyond the main phyllaries. Purple ragwort [Senecio elegans L.] is an escaped ornamental annual from South Africa that grows on disturbed sites along the Central and South Coast. It is easily distinguished from other ragworts by its purple ray flowers.

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Prevention: Tansy ragwort is an aggressive biennial in the Asteraceae family. Native to the Mediterannean, it was introduced into northern California and the Pacific Northwest in the early 1900's and is now a problem in forest clearings, pastures and disturbed areas across the region.
Tansy ragwort is highly poisonous to cattle and horses and also toxic to goats. The responsible compounds are pyrrolizidine alkaloids that are converted to toxic pyrroles in the liver. Cattle are poisoned after ingesting only 2-8% of their body weight. The toxic effects are often sublethal or only become apparent several months after ingestion due to irreparable liver damage. Sheep are generally not poisoned by tansy ragwort and may be used in control strategies.
Normally, cattle and horses will avoid grazing tansy ragwort due to its bitter taste. However, in heavily infested areas, or where tansy ragwort occurs in close association with desirable forage species, consumption is more likely due to limited selectivity in grazing.
Seed production may exceed 150,000 seeds per plant and seed viability in the soil can exceed three years. Tansy ragwort seed is primarily dispersed by wind (generally less than 10 m), water, animal hair or fur, and human related activities such as hay and straw transport. The spread of tansy ragwort can be reduced by using certified weed free hay and preventing overgrazing.
Oxford ragwort is an annual or bienniel herb that is not currently known to be in California. A single population was previously eradicated from the Berkeley Botanic Garden. However, in England, this species escaped from the Oxford Botanic Garden in the 19th century and rapidly spread across Southern England. There is no information available concerning management practices for Oxford ragwort. Therefore, the following information is based upon management practices for Senecio jacobaea.

Mechanical: Mowing tansy ragwort during the early flowering stage can reduce seed production. However, this generally stimulates new shoot production from the crown and a second crop of short-stemmed flowers is produced. Additionally, mowed plants may survive as short-lived perennials into the next year and produce a greater seed crop than unmowed plants. Repeated mowing of regrowth in the bud stage will reduce the secondary seed crop. It is critical to clean any mowing equipment after working in infested areas to prevent spread to new areas.
The toxic alkaloids remain in cut stems for a considerable time period following mowing and animals should not be allowed to graze recently mowed areas. One of the most important avenues for livestock poisoning is through ingestion of contaminated hay. Tansy ragwort patches should be avoided during hay cutting operations.
Hand pulling is effective on small infestations. It is important to remove the root system to prevent regrowth from the crown and root buds of the plant. If plants have set seed, they should be carefully removed, bagged, and burned.
Repeated tillage is an effective method for tansy ragwort control, however, tansy ragwort is generally not a problem in areas where tillage can be used. Regeneration of plants may occur from severed roots and crowns and tillage equipment should be cleaned after being used in infested areas.

Biological: Tansy ragwort is one of the best examples of effective classical biological control. There are three insects in California that have been approved and released for tansy ragwort control: the ragwort flea beetle (Longitarsus jacobaeae), ragwort seed fly (Pegohylemyia seneciella), and cinnabar moth (Tyria jacobaeae). The damage inflicted by these insects is often complementary. The flea beetle larvae feed on the roots and crowns and the adult beetles feed on the leaves. The seed fly larvae feed within the seed heads and the cinnabar moth larvae feed on the leaves, buds and flowers.
Flea beetles can be collected in the fall on new rosettes. The typical method of collection is a specialized vacuum apparatus. The adults can be transported in cool cardboard boxes with ample rosette leaves for food to new sites for release. A population of 250-500 insects is necessary for establishment. Establishment of populations may take up to five years. However, once established, these insects have provided greater than 90% tansy ragwort control in western Oregon and Washington and northern California.
Cinnabar moth larvae are easily recognized by black and yellowish-orange bands. They are effectively distributed by collecting several hundred larvae and transporting them in cool, cardboard boxes to new infestations. The larvae must be supplied with ample food during the transport process. The seed fly is already widely distributed in infested areas. When used alone, the seed flies are ineffective in reducing the tansy ragwort population.
Sheep may also be used for tansy ragwort control. Sheep are normally quite tolerant to tansy ragwort and will preferentially graze it in the summer. Continuous sheep grazing may prevent tansy ragwort from setting seed. However, this may also extend the life of the plants an additional year. Intensive sheep grazing in tansy ragwort infested areas has also been used as a pasture preconditioner for cattle.

Fire: There is little information regarding the use of fire for tansy ragwort control. Burning at the early flowering stage may reduce seed production. However, resprouts from the crown and seedling flushes in the following year are highly likely. In addition, exposed soils are susceptible sites for rapid re-establishment of tansy ragwort from wind dispersed seed.

Chemical: Tansy ragwort is susceptible to most auxin type herbicides in the seedling stage. 2,4-D in the LV ester or amine formulations at 1-2 lb ae/A is most effective when applied during the rosette stage and control decreases as plants begin to bolt. Dicamba (1 lb ae/A) is effective when applied from the rosette to bud stage. Picloram (0.25 lb ae/A) is not commercially available in California, but is effective up to the flowering stage. Clopyralid has given mixed results in studies and is not recommended as a stand-alone treatment. Metsulfuron (0.6 oz ai/A) plus a surfactant is effective on actively growing plants. Triclopyr plus 2,4-D (0.375 lb ae/A+ 1.0 lb ae/A) can be applied to plants in the rosette to early bud stages.
These treatments may not provide complete control and regrowth is likely to occur. Fall applications followed by a second spring application to any regrowth is more effective. Always consult the herbicide label for specific directions and restrictions.

Integrated Pest Management: The use of the biocontrol agents is probably the most effective long-term management strategy. However, occasional flare-ups in the population are likely, until the biocontrol agents build up enough to provide control. Flare-ups should be checked for the insects and supplemented if few insects are found.

Bedell, T.E., R.E. Whitesides, and R.B. Hawkes. 1981. Pasture management for control of tansy ragwort. Pacific Northwest Cooperative Extension Publication No. 210.
Brewster, B.D., M.P. Rolston, and A.P. Appleby. 1978. Control of tansy ragwort in western
Oregon pastures with 2,4-D. Oregon State University Agric. Exper. Stat. Circular 665.
Cairns, D. 1938. Vegetative propagation of ragwort. New Zeal. J. Sci. Technol. 20:173a-183a.
Cameron, E. 1935. A study of the natural control of ragwort (Senecio jacobaea L.). J. Ecol.
Frick, K.E. and L.A. Andres. 1967. Host specificity on the ragwort seed fly. J. Econ. Entomol.
Green, H.E. 1937. Dispersal of Senecio jacobaea. J. Ecol. 25:569.
Harper, J.L. 1965. Establishment, aggression and cohabitation in weedy species. Pp. 243-268 in
H.G. Baker and G.L. Stebbins (eds.), the genetics of colonizing species. Academic Press, NY.
Harper, J.L. and W.A. Wood. 1957. Biological flora of the British Isles: Senecio jacobaea L. J.
Ecol. 45:617-637.
Isaacson, D.L. and D.T. Ehrensing. 1977. Biological control of tansy ragwort. Oregon Dept. of
Agriculture, Weed Control Bulletin No. 1.
Meijden, E. van der and R.E. van der Waals-kooi. 1979. The population ecology of Senecio
jacobaea in the Netherlands sand dune system. I. Reproductive strategy and the biennial habit. J. Ecol. 67:131-154.
Sharrow, S.H. and W.D. Mosher. 1982. Sheep as a biological control agent for tansy ragwort. J.
of Range Management 35:480-482.
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