Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Senecio jacobaea
(common ragwort)



Senecio jacobaea (common ragwort)


  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Host Plant
  • Preferred Scientific Name
  • Senecio jacobaea
  • Preferred Common Name
  • common ragwort
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • S. jacobaea has spread rapidly in Canada, the north-western and Pacific States of the USA, New Zealand and Tasmania and the southern states of Australia following its accidental introduction from Europe over the last 150 years. In the absence of rigo...

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S. jacobaea: habit of flowering plant, Oxford, UK.
CaptionS. jacobaea: habit of flowering plant, Oxford, UK.
CopyrightStephen A. Harris
S. jacobaea: habit of flowering plant, Oxford, UK.
HabitS. jacobaea: habit of flowering plant, Oxford, UK.Stephen A. Harris
Rosette stage of S. jacobaea, Oxford, UK.
CaptionRosette stage of S. jacobaea, Oxford, UK.
CopyrightStephen A. Harris
Rosette stage of S. jacobaea, Oxford, UK.
RosetteRosette stage of S. jacobaea, Oxford, UK.Stephen A. Harris
S. jacobaea: habit of flowering plant, Oxford, UK.
CaptionS. jacobaea: habit of flowering plant, Oxford, UK.
CopyrightStephen A. Harris
S. jacobaea: habit of flowering plant, Oxford, UK.
HabitS. jacobaea: habit of flowering plant, Oxford, UK.Stephen A. Harris
Inflorescence of S. jacobaea, Oxford, UK.
CaptionInflorescence of S. jacobaea, Oxford, UK.
CopyrightStephen A. Harris
Inflorescence of S. jacobaea, Oxford, UK.
InflorescenceInflorescence of S. jacobaea, Oxford, UK.Stephen A. Harris


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Preferred Scientific Name

  • Senecio jacobaea L.

Preferred Common Name

  • common ragwort

Other Scientific Names

  • Jacobaea vulgaris Gaertn.
  • Senecio dimorphocarpos Col.

International Common Names

  • English: ragweed; ragwort; tansy ragwort
  • Spanish: hierba lombriguera
  • French: herb St. Jacques
  • Russian: krestovnik yakova
  • Portuguese: tasna; tasneira

Local Common Names

  • Austria: Jacobs-Kreuzkraut
  • Canada: baughlan
  • France: fleur de Saint-Jacques; herbe dorée; seneçon Jacobée
  • Germany: Jacobs-Kreuzkraut
  • Hungary: Jakabnapi aggófû
  • Ireland: benweed
  • Italy: erba san Jacobo; jacobea
  • Netherlands: Jakobskruiskruid
  • Norway: landoyda
  • Poland: starzec jakubek
  • Romania: jakabnapi aggófu; petimbroasa
  • Sweden: vanliga Jacobsörten
  • Switzerland: Jacobs-Kreuzkraut
  • UK: bragweed; bunnel; bunwede; bunweed; cammock; cankerweed; cankerwort; cheadle-dock; cow foot; cows foot; cradle-dock; cushag; devil dums; dog standard; fairies' horse; felon weed; field ragwort; fizz gigs; flee dod; fleenurt; fleewort; fly flower; gander-goose; gipsy; grand swaith; hammerwort; herb St. James; kadle-dock; kedlock; ketlock; marefart; mountain ragwort; muggart; muggart Kail; ragged Jack; ragged Robin; rayless ragwort; scattle-dock; scrape-clean; scrog; seg rum; seggy; sigrum; sleepy-dose; St. James' flower; staggerwort; stammer wort; stanerwort; stinking alisander; summer's farewell; swine's cress; swine's grass; tansy; tirso; water groundsel; weeby; wild chrysanthemum; yack-yard; yallers; yarkrod; yellow daisy; yellow elshinders
  • USA: cankerweed; fairies-horse; felon weed; kettle-dock; Saracen's compass; St. James' wort; staggerwort; stavewort

EPPO code

  • SENJA (Senecio jacobaea)

Summary of Invasiveness

Top of page S. jacobaea has spread rapidly in Canada, the north-western and Pacific States of the USA, New Zealand and Tasmania and the southern states of Australia following its accidental introduction from Europe over the last 150 years. In the absence of rigorous phytosanitary controls, it is likely to spread further, especially where land is poorly managed and overgrazed. S. jacobaea is undesirable because of its prolific seed production, vigorous growth and toxicity, leading to the invasion of pastureland and the consequent toxic effects on livestock.

Taxonomic Tree

Top of page
  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Asterales
  •                         Family: Asteraceae
  •                             Genus: Senecio
  •                                 Species: Senecio jacobaea

Notes on Taxonomy and Nomenclature

Top of page The complex patterns of morphological variation in the native range of S. jacobaea have led to the description of many infraspecific taxa (e.g., Hegi, 1987). However, the legitimacy and synonymy of these names is unclear. Within the UK, the major intraspecific variation appears to occur in the coastal populations (Kadereit and Sell, 1986). Kadereit and Sell (1986) recognize three intraspecific taxa: (i) subsp. jacobaea var. jacobaea (syns S. jacobaea var. discoideus Wimmer & Grab.; S. flosculosus Jordan; S. jacobaea var. stenoglossus Brenan & Simpson) is the typical taxon; (ii) subsp. jacobaea var. condensatus (syn. S. jacobaea var. abrotanoides Druce) is a coastal taxon; and (iii) subsp. dunensis (Dumort.) Kadereit & P.D. Sell (syn. S. jacobaea var. flosculosus Lam. & DC.) is another coastal taxon. S. jacobaea subsp. dunensis differs from subsp. jacobaea in having a single stem, up to 30 cm (rarely 60 cm) high, peduncles with a dense arachnoid indumentum, ray florets absent or rudimentary and hairy outer achenes. S. jacobaea var. condensatus differs from var. jacobaea in having stems that are markedly swollen below the basal leaves, a denser inflorescence and leaves and short, narrow ligules (5-7(-9 mm) long by 1-2 mm wide). The distinctions between some Senecio species and S. jacobaea are controversial, e.g., S. borysthenicus (DC.) Stankov and S. erraticus Bertol. [S. aquaticus subsp. erraticus (Bertol.) Matthews] (Chater and Walters, 1976; Pignatti, 1982).

Based on DNA sequence data from the chloroplast and nuclear genomes, Pelser et al. (2002) showed that Senecio section Jacobaea was monophyletic, and that of the 15 section Jacobaea species sampled, S. jacobaea was found in a monophyletic clade that comprised S. chrysanthemoides DC., S. cineraria DC., S. ambiguous DC., S. alpinus (L.) Scop., S. aquaticus Hill, S. pancicii Degen and S. subalpinus Koch.

Fisher (1932) suggests two origins of the vernacular name 'ragwort': (i) as a reference to the somewhat ragged leaf of the mature plant; and (ii) from the Anglo Saxon 'aege' meaning 'goat' and 'wort' meaning 'plant' with (fanciful) reference to the apparent similarity of the fruit heads to a goat's beard. Grigson (1974) supports the former view, and considers the name 'ragwort' to be of 15th century origin. Hunt (1989) gives regedewort and electarus as Medieval English names for S. jacobaea. Staggerwort appears to be a reference to the toxic effects of S. jacobaea on livestock, although Grieve (1931) cites an unnamed source to indicate that S. jacobaea was a remedy for staggers in horses! St. James' wort and the Italian, French and German vernacular names and the scientific name are a reference to the plant flowering around St. James' day (25th July). In about 1831, John Clare (Williams and Williams, 1986) famously wrote 'The Ragwort' about the beauty of S. jacobaea, and it attracted the 'poetic' attention of Barker (1925).

In databases and on the Web, the 'ae' diphthong in 'jacobaea' is often, incorrectly, transcribed as either 'jacobea' or 'jacobae'.


Top of page Herbaceous biennial, winter annual or short-lived perennial (usually monocarpic), (20-)80-150 cm tall, arising from a poorly developed to evident tap root. Stems are erect, arising singly or in clusters from an erect caudex, branching only in the inflorescence. Leaves alternate, often petiolate, becoming reduced in size upward, broadly ovate to ovate, deeply, bi- or tri-pinnatifid, 7-20 cm long and 2-6 cm wide. Basal leaves form a rosette, first leaves ovate, blunt, successive leaves lyrate-pinnatifid with 0-6 pairs of lateral lobes, early deciduous. Upper leaves more or less amplexicaul, auricles laciniate. Leaves differ in the degree of dissection, width of the lobes and in the presence of cottony hairs on the abaxial surfaces. Inflorescence broadly corymbiform and cymose with 20-60 capitula. Capitula (7-)12-25 mm diameter, usually radiate, involucral bracts oblanceolate (c. 13), acute, ±glabrous, dark-tipped, 3-4 mm long; few (ca. 5) subulate shorter bracts. Ray florets 12-15 (usually 13), female, ligule yellow, 8-12 mm long x 1-3 mm wide. Disc florets numerous, perfect, tube yellow, 5-7 mm long. Achenes ca. 8-ribbed, 2 mm long x 0.6 mm diameter, ray floret achenes are usually glabrous, those of disc, pubescent along ribs. Pappus white, twice as long as achenes, readily detached (especially from ray floret achenes).

Plant Type

Top of page Biennial
Seed propagated
Vegetatively propagated


Top of page S. jacobaea is considered native to Eurasia, the distribution extending as far west as Siberia and south as Asia Minor. However, the eastern and southern limits of the native distribution are difficult to define due to the extension of the range through man's activities. Records for Algeria and Turkey need confirmation since they may have been confused with S. erraticus (Davis, 1975) and S. aquaticus (Quezel and Santa, 1963), respectively. References have been made in the literature to the occurrence of S. jacobaea in South Africa and Argentina (e.g. Harper and Wood, 1957; Holm et al., 1979), although no recently published information can be found. In Canada, reports from Manitoba need to be investigated further, because these may be partly or wholly referable to S. eremophilus (Scoggan, 1979). Duthie (1875) reported S. jacobaea from Comino (Malta), but the record was accepted by neither Borg (1927) nor Haslam et al. (1977).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes


ArmeniaPresentNativeKomarov et al., 1961
AzerbaijanPresentNativeKomarov et al., 1961
ChinaPresentNativeHultén & Fries, 1986
Georgia (Republic of)PresentNativeKomarov et al., 1961
JapanPresentPresent based on regional distribution.
-HokkaidoPresentIntroducedIgarashi and Kosugi, 2012
KazakhstanPresentNativeKomarov et al., 1961
KyrgyzstanPresentNativeKomarov et al., 1961
LebanonPresentNativeUSDA-ARS, 2003
MongoliaPresentNativeKomarov et al., 1961
SyriaPresentNativeUSDA-ARS, 2003
TajikistanPresentNativeKomarov et al., 1961
TurkeyPresentNativeDavis, 1975
TurkmenistanPresentNativeKomarov et al., 1961
UzbekistanPresentNativeKomarov et al., 1961


AlgeriaPresentNativeQuezel and Santa, 1963
South AfricaAbsent, formerly presentIntroducedHolm, 1979; Harper and Wood, 1957; Holm et al., 1979

North America

CanadaPresentPresent based on regional distribution.
-British ColumbiaWidespreadIntroducedc. 1913 Invasive Harris et al., 1971; Scoggan, 1979
-ManitobaPresentIntroducedScoggan, 1979
-New BrunswickWidespreadIntroducedpre-1884 Invasive Macoun, 1884
-Newfoundland and LabradorWidespreadIntroduced Invasive Scoggan, 1979
-Nova ScotiaWidespreadIntroducedc. 1853 Invasive Macoun, 1884; Erskine, 1960
-OntarioWidespreadIntroducedc. 1861 Invasive Macoun, 1884; Bain, 1991
-Prince Edward IslandWidespreadIntroducedc. 1888 Invasive Erskine, 1960
-QuebecWidespreadIntroduced1904 Invasive Scoggan, 1979; Bain, 1991
Saint Pierre and MiquelonWidespreadIntroduced Invasive Scoggan, 1979
USAPresentPresent based on regional distribution.
-CaliforniaWidespreadIntroduced1912 Invasive
-IdahoPresentIntroduced1987Burrill et al., 1994
-IllinoisRestricted distributionIntroduced
-MichiganRestricted distributionIntroduced
-New JerseyPresentIntroduced
-New YorkPresentIntroducedTaylor, 1915
-OregonWidespreadIntroduced1922 Invasive Isaacson, 1978
-PennsylvaniaPresentIntroducedBritton and Brown, 1936
-WashingtonWidespreadIntroduced Invasive

Central America and Caribbean

Trinidad and TobagoPresentIntroducedHolm et al., 1979

South America

ArgentinaAbsent, formerly presentIntroducedHolm, 1979; Harper and Wood, 1957; Holm et al., 1979
BrazilPresentIntroducedHolm et al., 1979
UruguayPresentIntroducedHolm et al., 1979


AlbaniaWidespreadNativeHayek, 1931; Chater and Walters, 1976
AndorraPresentNativeChater and Walters, 1976
AustriaWidespreadNativevon Mannagetta, 1892; Chater and Walters, 1976
BelarusWidespreadNativeKomarov et al., 1961
BelgiumWidespreadNativeReichenbach and Reichenbach, 1854; de and Wildeman Durand, 1899; Chater and Walters, 1976
Bosnia-HercegovinaWidespreadNativeHayek, 1931; Chater and Walters, 1976
BulgariaWidespreadNativeHayek, 1931; Stoianov and Stephanov, 1948; Chater and Walters, 1976
CroatiaWidespreadNativeHayek, 1931; Chater and Walters, 1976
Czech RepublicPresentHodálová et al., 2007
Czechoslovakia (former)WidespreadNativeChater and Walters, 1976
DenmarkWidespreadNativePetersen, 1999; Reichenbach & Reichenback, 1854; Chater and Walters, 1976
EstoniaWidespreadNativeKomarov et al., 1961; Chater and Walters, 1976
FinlandRestricted distributionIntroducedChater and Walters, 1976
FranceWidespreadNative Invasive Rouy, 1903; Chater and Walters, 1976
-CorsicaWidespreadNativeRouy, 1903; Chater and Walters, 1976
GermanyWidespreadNative Invasive Reichenbach and Reichenbach, 1854; Sturms, 1905; Chater and Walters, 1976
GreeceWidespreadNativede Halácsy, 1902; Hayek, 1931; Chater and Walters, 1976
HungaryWidespreadNativeReichenbach and Reichenbach, 1854; Chater and Walters, 1976
IrelandWidespreadNative Invasive Chater and Walters, 1976
ItalyWidespreadNativeChater and Walters, 1976; Pignatti, 1982
LatviaWidespreadNativeKomarov et al., 1961; Chater and Walters, 1976
LiechtensteinWidespreadNativeMurr, 1924; Chater and Walters, 1976
LithuaniaWidespreadNativeKomarov et al., 1961; Chater and Walters, 1976
LuxembourgWidespreadNativeChater and Walters, 1976
MacedoniaWidespreadNativeHayek, 1931; Chater and Walters, 1976
MaltaAbsent, formerly presentDuthie, 1875
MoldovaWidespreadNativeChater and Walters, 1976
NetherlandsWidespreadNative Not invasive Reichenbach and Reichenbach, 1854; Chater and Walters, 1976; Heukels and van der Meijden, 1983
NorwayWidespreadNativeLid, 1944; Chater and Walters, 1976
PolandWidespreadNativeChater and Walters, 1976
PortugalWidespreadNativeChater and Walters, 1976; Franco, 1984
RomaniaWidespreadNativeSavulescu, 1964; Chater and Walters, 1976
Russian FederationPresentPresent based on regional distribution.
-Central RussiaWidespreadNativeChater and Walters, 1976
-Eastern SiberiaWidespreadNativeKomarov et al., 1961
-Northern RussiaPresentChater and Walters, 1976
-Southern RussiaWidespreadNativeKomarov et al., 1961
-Western SiberiaWidespreadNativeKomarov et al., 1961
SerbiaWidespreadNativeHayek, 1931; Rohlena, 1942; Chater and Walters, 1976
SlovakiaWidespreadNativeChater and Walters, 1976
SloveniaWidespreadNativeChater and Walters, 1976
SpainRestricted distributionNative Not invasive Willkomm and Lange, 1870; Merino, 1906; Chater and Walters, 1976
SwedenWidespreadNativeNyman, 1867; Chater and Walters, 1976
SwitzerlandWidespreadNativeReichenbach and Reichenbach, 1854; Chater and Walters, 1976
UKWidespreadNative Invasive Chater and Walters, 1976; Stace, 1997
-Channel IslandsWidespreadNativeMcClintock, 1975; Le Sueur, 1984
-England and WalesPresentDixon and Clay, 2001
UkraineWidespreadNativeKomorov et al., 1961; Chater and Walters, 1976
Yugoslavia (former)WidespreadNativeBoissier, 1875; Hayek, 1931; Chater and Walters, 1976


AustraliaPresentPresent based on regional distribution.
-South AustraliaRestricted distributionIntroduced1954 Invasive Black, 1957
-TasmaniaWidespreadIntroduced Invasive McLaren et al., 2000
-VictoriaRestricted distributionIntroduced1880-1890 Invasive Schmidl, 1972
-Western AustraliaPresentIntroducedDepartment of Agriculture - Western Australia, 2002
New ZealandWidespreadIntroduced1874 Invasive Allan, 1940

History of Introduction and Spread

Top of page All introductions of S. jacobaea outside of the native range appear to have been accidental. The earliest records (1850s) for the introduction of S. jacobaea into Canada are into Nova Scotia as a ballast alien (Harris et al., 1971), with records from Prince Edward Island in 1888, where it was reported as common in 1900 (Catling et al., 1985). Collections were made from New Brunswick (1891) and Quebec (1904), with sporadic collections from Ontario (1861 and 1903; Bain, 1991). The introduction to British Columbia appears to have occurred around 1913 (Harris et al., 1971). In the USA, S. jacobaea was recorded from California in 1912 and Oregon in 1922 (Isaacson, 1978), although there are early records of S. jacobaea as an adventive in New York (Taylor, 1915) and Philadelphia (Britton and Brown, 1936). By the mid-1950s S. jacobaea was a significant weed on the Pacific coast. There is one report of S. jacobaea from Idaho in 1987 (Burrill et al., 1994). The greatest infestations are west of the Cascades, although there are reports of S. jacobaea starting to invade east of the Cascades.

S. jacobaea was introduced to Victoria (Australia) from Europe between 1880 and 1890 (Schmidl, 1972), and is a particular problem in the south-east of the state. The first record from South Australia was in 1954 (Black, 1957). Localized outbreaks occur in the high rainfall (>750 mm) areas of Western Australia (Department of Agriculture - Western Australia, 2002). In New Zealand, S. jacobaea was first reported in 1874 (Allan, 1940), and is common over both the North and South Islands.

Harper and Wood (1957), and subsequent authors, identified S. jacobaea as an exotic in South Africa and Argentina. However, a search of the recent flora records for these two countries revealed no references to the occurrence of S. jacobaea; although other hepatotoxic Senecio species do occur in these countries. Grime et al. (1988) argue that S. jacobaea may be declining in many areas of the UK, although Preston et al. (2002) note that the distribution of S. jacobaea does not appear to have changed over the last 40 years.

Risk of Introduction

Top of page Further spread is highly probable, owing to the risks of both accidental movement as an achene contaminant of agricultural produce, deliberate introduction as a herbal plant, and, less likely, as an ornamental.

S. jacobaea is one of five species listed under the UK Weeds Act 1959 and the Town and Country Planning Act 1990. In the Weeds Act, primary responsibility for control rests with the occupier of any land on which the plants are growing. Where there is a risk that S. jacobaea might spread, the Minister of Agriculture can serve a notice on the occupier of the land requiring action to be taken to prevent its spread (Roberts, 1982). However, in practice, 'priority is given to those complaints where there is a threat to farmland or land that is being used for the keeping of horses as part of a diversified farm business' (Alun Michael, House of Commons, UK, 7th November 2002); pressure groups interested in equines are campaigning to amend the Weeds Act 1959, although such campaigns have been criticised (Cook, 2003).

S. jacobaea is listed as a prohibited noxious weed (Class I) under the Canada Seeds Order (Anon., 1986a), and is listed under Weed Control Acts in British Columbia and Nova Scotia (NSDAM, 1977; Anon., 1986b). S. jacobaea is covered by Federal and State quarantine laws in Arizona, California, Colorado, Idaho, Montana and Washington (National Plant Board, 2003). In addition, S. jacobaea is listed as a noxious weed in Colorado (Colorado State Code, 2000) and Idaho (Idaho Department of Agriculture, 1993), a prohibited noxious weed in Arizona (Arizona Department of Agriculture, 1996), a Class B noxious weed in California (California Department of Food and Agriculture, 1998) and Washington (Washington Department of Agriculture, 1992, 1997) and Class B designated weed in Oregon (Oregon Department of Agriculture, 1997a, b).

In Australia, S. jacobaea is a proclaimed plant that is notifiable throughout the state of South Australia, under the Animal and Plant Control Act 1986 (Animal & Plant Control Commission, 1999). In Tasmania, S. jacobaea is a noxious weed under the Noxious Weeds Act 1964 and the Weed Management Act 1999 (DPIWE, 2003). In Western Australia, S. jacobaea is a declared noxious weed (Department of Agriculture - Western Australia, 2002). In New Zealand, S. jacobaea is prohibited under the Biosecurity Act 1993 (MAF Biosecurity Authority, 2002).


Top of page In its European range, S. jacobaea is a native of sand dune communities, as well as woodland and grassland communities (Harper and Wood, 1957). However, it is more commonly found associated with man, especially on overgrazed grassland and poorly managed cultivated land. Increasingly, in Europe and its introduced range, it is associated with waste places, railways and roadsides (Watt, 1987). Generally, S. jacobaea prefers mesic habitats. In Australia, S. jacobaea is found in high rainfall areas (Schmidl, 1972), whilst in New Zealand it is found where rainfall exceeds 870 mm/year (Wardle, 1987). More commonly, S. jacobaea is found on lighter, well-drained soils and with a pH greater than 7.

Habitat List

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Coastal areas Present, no further details Harmful (pest or invasive)
Disturbed areas Present, no further details Harmful (pest or invasive)
Managed forests, plantations and orchards Present, no further details
Managed grasslands (grazing systems) Present, no further details Harmful (pest or invasive)
Rail / roadsides Present, no further details Harmful (pest or invasive)
Urban / peri-urban areas Present, no further details
Natural grasslands Present, no further details Harmful (pest or invasive)

Hosts/Species Affected

Top of page S. jacobaea is not normally a weed of crops but it will colonize set-aside (Welch, 1995) and is a major concern wherever poorly managed and overgrazed pasture occurs (Ralphs, 2002).

Biology and Ecology

Top of page Genetics

A chromosome number of 2n = (4x) = 40 has commonly been reported for European material, although 2n = (8x ) = 80 has also been recorded (e.g., Bolkhovskikh et al., 1969; Moore, 1973). Chromosome number appears to be independent of infraspecific boundaries (Kadereit and Sell, 1986). Böcher and Larsen (1955) record a chromosome number of 2n = 32 (which needs to be confirmed) from S. jacobaea material collected from sand dunes in County Donegal (Ireland), which Kadereit and Sell (1986) suggest might be S. jacobaea subsp. jacobaea var. condensatus. Hybridization is recorded in the UK and Ireland with S. aquaticus L. (as S. x ostenfeldii Druce), S. erucifolius L. (as S. x liechtensteinensis Murr., syn. S. x whitwellianus Lees ex Cheetham nomen nudum) and S. cineraria DC. (a garden escape in the UK; as S. x albescens Burbridge & Colgan) (Benoit et al., 1975), in Germany with S. aquaticus (Hegi, 1929), in Austria and Liechtenstein with S. erucifolius (Hegi, 1929) and in Germany, Austria, Tyrol and Switzerland with S. alpinus (L.) Scop. (as S. x reisachii Gremblich and S. x eversii Huter; Hegi, 1929). Chater and Walters (1976) indicate that hybrids between S. jacobaea and S. aquaticus occur occasionally in Central and Western Europe. Benoit et al. (1975) question the reliability of the UK and Continental records of hybrids between S. jacobaea and S. erucifolius, and the Irish records of hybridization between S. jacobaea and S. squalidus. Hybrids between S. aquaticus and S. jacobaea are partially fertile, morphologically variable and often form hybrid swarms (Harper and Wood, 1957; Benoit et al., 1975); such hybrids are generally lowland < 350 m) and particularly common in the north and west of the UK and Ireland (Preston et al., 2002). Hybrids between S. cineraria and S. jacobaea are partially fertile and morphologically variable, most often similar to S. jacobaea (Harper and Wood, 1957; Benoit et al., 1975); such hybrids appear to be spreading in the UK and Ireland either as garden escapes or through spontaneous crossing (Preston et al., 2002). Hybrids between S. jacobaea and S. alpinus are widely distributed in Germany, Tyrol and Switzerland (Hegi, 1929). Generally, the distribution of hybrids in continental Europe is poorly understood; hybrids may have been under-recorded for the parents. The occurrence of hybrids in the introduced range of S. jacobaea is unknown. There appears to have been no investigation of neutral DNA marker variation in either the native or introduced ranges of S. jacobaea.

Physiology and Phenology

In a population of S. jacobaea from Aberdeenshire (Scotland, UK), Forbes (1977) showed that of the plants which flowered in the first two years, or survived into a third year, 8% were annual, 39% were biennial and 53% perennial. Otzen (1977) has suggested that flowering individuals have significant carbohydrate reserves in the stem bases and roots, which may allow S. jacobaea to behave as a facultative perennial.

S. jacobaea contains pyrrolizidine alkaloids (PAs), some of which are highly toxic to animals and humans (Mattocks, 1986). PAs have been described from 459 species in 16 plant families (Rizk, 1991), although only six families contain hepatotoxic PAs (WHO, 1988). The most important families (genera) are: Boraginaceae (Heliotropium), Asteraceae (Senecio) and Fabaceae (Crotalaria). Numerous reviews have been published on the chemistry and toxicology of PAs (e.g., Bull et al., 1968; Mattocks, 1986; Rizk, 1991; Hartmann, 1999). PAs are not toxic to mammals per se, rather the hazard arises through the normal oxidative detoxification mechanisms in the liver that convert them to pyrrolic metabolites (dehydroalkaloids; Mattocks, 1986). Hepatotoxicity or carcinogenicity of these highly reactive electrophilic alkylating agents is a result of their binding to nucleophilic centres in tissues or to cross-link DNA (Mattocks, 1986; Woo et al., 1993; Stegelmeier et al., 1999; Kim et al., 1999; Fu et al., 2001).

Nine PAs are known from the aerial parts of S. jacobaea: jacobine, jacoline, jacocine, jacozine, senecionine, seneciphylline, olosenine, retrosine and senkirkine (Mattocks, 1986; Rizk, 1991;), of which the first six are the most important. It is known that there is considerable plant-to-plant variation in the total PA concentration and concentration of individual PAs (Witte et al., 1992). Herbivory by the adults and larvae of the specialist flea beetle Longitarsus jacobaeae and non-specialist insects, are negatively correlated with PA concentration (Vrieling and van Wijk, 1994; Vrieling and de Boer, 1999). Witte et al. (1992) identified two chemotypes among European populations of S. jacobaea, one the 'jacobine-type' (profile dominated by jacobine, jacoline, jacocine, jacozine, senecionine and seneciphylline) and the other 'erucifoline-type' (dominated by erucifoline, with only traces of PAs from the 'jacobine-type'); these two chemotypes may reflect crossing with S. erucifolius. There appears to be a strong genetic component of variation in PA content between S. jacobaea plants (Vrieling et al., 1993). In an investigation of two annual Senecio species (S. vernalis and S. vulgaris), Hartmann and Zimmer (1986) found that the highest PA content occurred in the capitula, and that PA concentration (1.0-1.4 mg/g fresh weight) was 5- to 10-fold higher than in the roots and leaves. Similar qualitative differences in PA distribution have been shown in S. jacobaea (Witte et al., 1992). There appears to be no significant reduction in the toxicity of S. jacobaea PAs when the leaves are dried (Goeger et al., 1982a; Cooper and Johnson, 1998). In fact, some evidence suggests that dried leaves and plants killed with herbicides are more palatable to livestock (Irvine et al., 1977).

Reproductive Biology

Capitula open when expanding disc florets force the involucral bracts apart; ray florets expand later giving S. jacobaea the initial appearance of being eradiate. Expansion and unrolling of ray florets occurs in less than 24 hours; stigmas are receptive as soon as the floret is expanded. Disc florets open later (centripetally). The capitula are visited by many types of insects, mainly Hymenoptera and Diptera (Cameron, 1935; Harper and Wood, 1957). Flowers produce both nectar and a faint odour, with pollen presentation in the UK between 08.00 and 17.00 h (peak 10.00-12.00 h; Harper and Wood, 1957). Within a single capitulum, anthers continue to dehisce over four to nine days (Harper and Wood, 1957). Rain limits both floret opening and anthesis. Andersson (2001) provides data which indicate that S. jacobaea is self-incompatible; probably with sporophytic self-incompatibility, in common with other members of the Asteraceae (Hiscock, 2000). Thus, S. jacobaea is an example of a successful self-incompatible colonizer (Brennan et al., 2002). In the UK, S. jacobaea is one of the most important species for Lepidoptera (Proctor et al., 1996).

Propagation is primarily by achenes, although vegetative propagation by roots may also occur (Poole and Cairns, 1940; Harper and Wood, 1957). The ray and disc florets of S. jacobaea produce heteromorphic achenes (Green, 1937; McEvoy, 1984). Disc floret achenes are light (mean weight = 199 µg), numerous (mean = 58 achenes per capitula) and equipped with a pappus, which aids wind transport, and rows of trichomes, which may aid animal transport (McEvoy, 1984). In contrast, ray achenes are heavy (mean weight = 286 µg), less numerous (mean = 13 achenes per capitula) and lack apparent dispersal structures (McEvoy, 1984). Disc achenes are released shortly after they mature, the parent may retain ray achenes for months after maturity (Green, 1937; McEvoy, 1984;), due to the latter being retained by the parent plant (Baker-Kratz and Maguire, 1984).

Individual S. jacobaea plants vary greatly in the numbers of achenes that they produce. Cameron (1935) indicates that 4700 to 174,000 achenes are produced per plant, with the higher number being an unusual plant that had been damaged by considerable grazing. Salisbury (1964) cites the example of a plant from the South Downs (UK) that he estimated to have produced c. 170,000. Van der Meijden and van der Waals-Kooi (1979) estimate that up to 30,000 achenes are produced by a single plant. S. jacobaea achene viability has been estimated as high as 80-90%, although lower levels (60%) have been estimated from late-flowering individuals (Salisbury, 1964; Schmidl, 1972; Baker-Kratz and Maguire, 1984). For a given weight, disc achenes have a higher germination percentage than ray achenes; germination time decreases with increasing achene weight in disc achenes, but increases with achene weight in ray achenes (McEvoy, 1984). Crawley and Nachapong (1985) have shown that S. jacobaea plants in the UK, defoliated by Tyria jacobaeae larvae, are capable of producing regrowth shoots that flower and produce achenes in early autumn of the same year. These regrowth achenes are significantly lighter (0.26 mg dry weight versus 0.41 mg dry weight), with a lower germination rate (78.8% versus 86.4%), compared to primary achenes.

In an experimental study, McEvoy and Cox (1987) showed that the majority (89%) of S. jacobaea achenes were dispersed within 5 m of the parent, despite differences arising from the height of release, wind direction, achene type and time of release. In contrast, Begon and Mortimer (1981) speculated that S. jacobaea achenes travel at least 15 m. Disc achenes were dispersed about twice as far as ray achenes (McEvoy and Cox, 1987). Dispersal distances are reduced by high atmospheric humidity due to achene trichomes becoming matted and the phyllaries closing around the achenes (Poole and Cairns, 1940). Animal dispersal of achenes may be important in some cases. For example, large numbers of S. jacobaea achenes are found in rabbit dung in eastern England (Pakeman et al., 1998; Pakeman et al., 1999).

Vegetative reproduction can occur from crown buds, excised root fragments and intact roots (Harper and Wood, 1957; Wardle, 1987). Schmidl (1972) reported that more than 35% of plants produced multiple crowns; disturbance or injury promotes vegetative reproduction. Vegetative rosettes form buds more readily than flowering plants (Poole and Cairns, 1940).

Information on achene longevity is conflicting. Achenes may remain viable for up to 15 years when stored dry. Thompson and Makepeace (1983) showed a decline in achene viability with depth of burial (achene viability declined to 1% in 10-16 years when buried under 4 cm soil). James et al. (2000), in a study to investigate achene longevity in relation to soil type and burial depth, showed that after 16 years, no viable achenes were found in a clay soil, whilst 1-3% of achenes remained viable in silt loam and peat soils, and up to 13% remained viable in sandy soils. Viability was greatest for the most deeply buried achenes (up to 18 years for achenes buried 19-21 cm deep).

Environmental Requirements

S. jacobaea is found in the drier regions of Europe and Asia (Harper and Wood, 1957). It can survive under most soil moisture conditions, even the hot, dry summers of the eastern part of the Pacific Northwest, and overwinters successfully in areas where temperatures reach -30°C when there is good snow cover. However, S. jacobaea tends to be found in more mesic areas. For example, in Australia and New Zealand it is found in high rainfall areas (Schmidl, 1972; Wardle, 1987), whilst in North America, it is established in areas with cool, wet, cloudy weather (Bain, 1991). In Oregon, S. jacobaea appears to be particularly well adapted to coastal areas or to inland areas that have some marine influence and a relatively moderate climate (Hawkes, 1981). Harper and Wood (1957) indicate that severe frost kills the aerial parts of the plant but regeneration can occur from the crown. Poole and Cairns (1940) state that young rosettes regenerating from root fragments are very liable to frost damage. Harper and Wood (1957) indicate that the distribution of S. jacobaea is probably not limited by climatic extremes in Eurasia, and the absence of grazing and cultivation at high altitudes limits distribution. The distribution of S. jacobaea is associated with moderate levels of distrubance and relatively unproductive conditions, although it is not excluded from any vegetation type except where disturbance is minimal (Grime et al., 1988; Clay et al., 2000).


Gange et al. (2002) report that S. jacobaea is weakly mycorrhizal.

Latitude/Altitude Ranges

Top of page
Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
0 0 0 0

Air Temperature

Top of page
Parameter Lower limit Upper limit
Absolute minimum temperature (ºC) -30
Mean annual temperature (ºC) 4 19
Mean maximum temperature of hottest month (ºC) 25 45
Mean minimum temperature of coldest month (ºC) -14 8


Top of page
ParameterLower limitUpper limitDescription
Dry season duration07number of consecutive months with <40 mm rainfall
Mean annual rainfall400mm; lower/upper limits

Rainfall Regime

Top of page Summer

Soil Tolerances

Top of page

Soil drainage

  • free

Soil reaction

  • acid
  • alkaline
  • neutral

Soil texture

  • light
  • medium

Special soil tolerances

  • infertile
  • shallow

Natural enemies

Top of page
Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Botanophila jacobaeae Herbivore Fruits/pods/Inflorescence
Botanophila seneciella Herbivore Fruits/pods/Inflorescence
Bremia lactucae Pathogen Seedlings
Cochylis atricapitana Herbivore Growing point
Coleosporium tussilaginis f.sp. senecionis-sylvati Pathogen Fruits/pods/Growing point/Inflorescence/Leaves/Stems
Longitarsus flavicornis Herbivore Growing point/Inflorescence/Leaves/Roots/Stems
Longitarsus jacobaeae Herbivore Growing point/Inflorescence/Leaves/Roots/Stems
Patagoniodes farinaria Herbivore
Pegohylemya jacobaeae Herbivore Australia
Podosphaera fusca Pathogen
Puccinia dioicae Pathogen Growing point/Inflorescence/Leaves/Stems
Puccinia expansa Pathogen
Puccinia glomerata Pathogen
Tyria jacobaeae Herbivore Growing point/Inflorescence/Leaves/Stems

Notes on Natural Enemies

Top of page Some lepidopteran larvae sequester pyrrolizidine alkaloids from S. jacobaea, the most important of which is Tyria jacobaeae (James et al., 1992), although McLaren (1992) has promoted the value of Cochylis atricapitana as a potential biological control agent for S. jacobaea in Australia. Harper and Wood (1957) and Cameron (1935) list insect herbivores and fungal pathogens found on S. jacobaea in the UK. Records of other insect species found feeding on S. jacobaea are scattered throughout the entomological literature (e.g., Philogene, 1973; McQuillan and Ireson, 1987). Potential fungal pathogens for S. jacobaea have been found in the introduced range of S. jacobaea (Johnston, 1990; Paul et al., 1993). For further information on natural enemies see Julien and Griffiths (1998).

Means of Movement and Dispersal

Top of page Natural Dispersal (Non-Biotic)

Achenes are wind-dispersed (perhaps poorly so; Wardle, 1987), although Poole and Cairns (1940) estimated that only about 0.5% of achenes were wind-dispersed. Achene dispersal distances range from 0 m to 14 m depending on conditions (McEvoy and Cox, 1987). The majority of achenes (89%) are dispersed within 5 m of the parent plant, and in no cases were achenes found to disperse more than 14 m from the parent plant. Schmidl (1972) indicates that achenes may be dispersed by water. McEvoy and Rudd (1993) have shown that disturbance is a major factor in establishment of S. jacobaea and populations are limited more by the availability of microsites for germination and establishment than by achene availability.

Vector Transmission (Biotic)

Humans and their animals transport achenes (Schmidl, 1972).

Agricultural Practices

Movement of hay is likely to spread the achenes, whilst set-aside creates ideal habitats for S. jacobaea establishment in the UK (Clay et al., 2000). The movement of livestock, and survival of achenes in faeces, is also likely to aid dispersal. Poor management of pasture provides ideal conditions for the establishment of S. jacobaea.

Accidental Introduction

S. jacobaea may be accidentally introduced by man, collecting the plants for ornament and then disposing on rubbish heaps; also as a result of movement of soil in the course of building works, and by attachment to vehicles or in the slip-stream of road and rail vehicles.

Intentional Introduction

Intentional introduction of S. jacobaea is unlikely, although there is an anecdotal account of inflorescences being offered for sale by enterprising UK farmers (Page, 1993).

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Clothing, footwear and possessionsFruits attached to clothes, shoes, etc. Yes
Containers and packaging - woodHay packaging Yes
Land vehiclesFarm vehicles, etc. Yes
Plants or parts of plantsLivestock feed Yes
Soil, sand and gravelAttached to vehicles Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Flowers/Inflorescences/Cones/Calyx fruits
Fruits (inc. pods) fruits
Growing medium accompanying plants fruits
Leaves fruits
Stems (above ground)/Shoots/Trunks/Branches fruits
Plant parts not known to carry the pest in trade/transport
Seedlings/Micropropagated plants
True seeds (inc. grain)

Impact Summary

Top of page
Animal/plant collections None
Animal/plant products Negative
Biodiversity (generally) Negative
Crop production None
Environment (generally) Negative
Fisheries / aquaculture None
Forestry production None
Human health None
Livestock production Negative
Native fauna None
Native flora Negative
Rare/protected species None
Tourism None
Trade/international relations Negative
Transport/travel None


Top of page The primary economic impact of S. jacobaea is through the reduction in pasture productivity where there are heavy infestations, and it is at this point that S. jacobaea poisoning is most likely to occur. Holm et al. (1979) indicate it as a 'principal' weed in New Zealand. S. jacobaea is one of the commonest causes of livestock poisoning in the UK (Cooper and Johnson, 1998; Noonan, 2001), whilst in the north-western USA poisoning has reached such proportions that it is a considerable economic problem (Johnson, 1982). For example, in the state of Oregon (USA), losses due to S. jacobaea infestations have been estimated to be approximately US$ 2-5 million annually (Snyder, 1972; Isaacson and Ehrensing, 1977). Coombs et al. (1996) estimate that the annual benefit of S. jacobaea control in Oregon is US$ 5 million, with S. jacobaea control being achieved at a cost of about $5/ha. In Australia, McLaren and Mickan (1997) estimated the total annual cost of S. jacobaea presence to be Au$ 4 million. In Australia and New Zealand, pyrrolizidine alkaloid (PA) toxicosis is a general cause of heavy livestock losses (Culvenor, 1985). Livestock generally avoid S. jacobaea because of the toxic PAs, although when it is present in hay, S. jacobaea will be eaten; Peterson and Culvenor (1983) have reviewed syndromes of PA poisoning in domesticated animals. Acute poisoning (and death) occurs from a large intake of the plant over a short period. However, chronic poisoning over a longer period is more usual, and results from sublethal poisoning over weeks or years (Bull et al., 1968; McLean, 1970; Mattocks, 1986); the long-term consequences of the consumption of sublethal PA doses on cattle production are unknown. Some animals develop a lethal addiction to, or preference for, the plant once they have started eating it (Cooper and Johnson, 1998).

S. jacobaea is primarily hepatotoxic (with renal megalocytosis and mild nephrosis) in animals, although it appears to be pneumotoxic in pigs (Harding et al., 1964; Bull et al., 1968). Livestock and equines differ widely in their sensitivity to PAs (WHO, 1988), sheep and goats (chronic lethal dose of S. jacobaea = 1.25-4.04 kg/kg body weight) are resistant, cattle and horses (chronic lethal dose = 0.05-0.2 kg/kg body weight) less so, and poultry and pigs, rather sensitive (Hooper, 1978). The resistance of sheep to PA poisoning has been ascribed to destruction of the alkaloids in the rumen by conversion into non-toxic 1-methylenepyrrolizidine derivatives (Bull et al., 1968; Craig et al., 1986). S. jacobaea toxicity remains in hay and dried grass and is reduced in silage, but not enough to be safe for consumption by cattle (Candrian et al., 1986); dried grass, hay or silage is the most common source of livestock poisoning (Giles, 1983; Leyland, 1985). In Oregon, Coombs et al. (1996) estimate that PA poisoning of livestock decreased by about 90% when S. jacobaea populations were controlled.

Environmental Impact

Top of page S. jacobaea competes with natural vegetation, reducing grass and other low-growing plants. This can lead to soil erosion as well as a loss in biodiversity.

Impact: Biodiversity

Top of page S. jacobaea can be a serious problem in species-rich grassland. The horizontally flattened rosettes can overtop and kill surrounding vegetation (McEvoy, 1984), which may explain why S. jacobaea persists in the absence of environmental disturbance. Watt (1987) cites the efforts of the Nature Conservancy Council to control S. jacobaea manually in UK National Nature Reserves. However, in its introduced range S. jacobaea may be an important species for endemic invertebrates. For example, 42 endemic or oligophagous insects or mites have been recovered from S. jacobaea on the Pacific Coast of North America (Frick, 1964; Frick and Hawkes, 1970; Frick, 1972).

Social Impact

Top of page The aetiology of pyrrolizidine alkaloid (PA) poisoning in humans was first described by Willmot and Robertson (1920; wheat flour contaminated with leaves and achenes of Senecio ilicifolius and S. burchellii), although similar symptoms were known in livestock as Molteno disease (South Africa), Winton's disease (New Zealand) and Pictou disease (Canada). The first case of livestock poisoning in the UK was reported in 1917 (Stockman, 1917). Human disease caused by PA toxicity is endemic to Central Asia, mainly because of staple food contamination by seed of Heliotropium species (Boraginaceae) (Tandon et al., 1976; Mohabbat et al., 1976; Tandon et al., 1978; WHO, 1988); most recently in Tajikistan (Chauvin et al., 1993; Mayer and Lüthy, 1993). PA poisoning from S. vulgaris achenes was reported in 1994 in a group of Bedouins in northern Iraq (Altaee and Mahmood, 1998). Additional cases of human toxicity have been recorded from the use of PA-containing plants in herbal remedies (Huxtable, 1980; Culvenor et al., 1986; Roulet et al., 1988; WHO, 1988; Röder, 1995, 2000). PA poisoning in humans is seen as veno-occlusive disease; a provisional tolerable daily PA intake is proposed at 1 µg/kg body weight/day (Ridker et al., 1985; ANZFA, 2001). There appear to be no cases of human death caused by the PAs derived from consumption of S. jacobaea.

PAs and/or toxic metabolites are secreted in the milk of lactating dairy cattle (Dickinson et al., 1976; Dickinson and King, 1978; Goeger et al., 1979; Deinzer et al., 1982; Goeger et al., 1982b; Molyneaux and James, 1990) and have been found in eggs (Edgar and Smith, 1999). However, since commercial milk supplies are bulked there is unlikely to be significant human exposure by this route (ANZFA, 2001), although S. jacobaea consumption rapidly reduces butterfat production in cattle (Miller, 1936). During PA poisoning epidemics, cases of veno-occlusive disease in suckling babies have been recorded (Roulet et al., 1988). PAs can been found in honey (Dickinson, 1976; Deinzer et al., 1977; Röder, 1995; Crews et al., 1997; Edgar et al., 2002). PA levels, at least as high as 3.9 µg/g honey, have been recorded from S. jacobaea honey, although such honey is not used commercially as it has an unpleasant flavour (Deinzer et al., 1977; Crews et al., 1997). However, the consequences of low level PA exposure for human health are unclear (ANZFA, 2001).

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • Highly adaptable to different environments
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Highly mobile locally
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
Impact outcomes
  • Negatively impacts agriculture
  • Negatively impacts animal health
  • Negatively impacts tourism
  • Reduced amenity values
  • Reduced native biodiversity
Impact mechanisms
  • Competition - monopolizing resources
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult to identify/detect as a commodity contaminant
  • Difficult to identify/detect in the field
  • Difficult/costly to control


Top of page Sharrow and Mosher (1982) suggested that S. jacobaea is a good feed for sheep during summer months, although the long-term effects of pyrrolizidine alkaloid (PA) exposure on sheep may be detrimental. Ernst and Leloup (1987) showed that S. jacobaea is a good atmospheric biomonitor for the pollutants iron, manganese and zinc.

S. jacobaea is an important food plant for many wild insect species in its native range. For example, Smith (1980) indicates that 84 insect species depend on S. jacobaea, including 33 lepidopterans. Furthermore, Wiggins (1977) reported that in a survey of Sussex (UK) wild flowers, S. jacobaea received more visits by insects than any other species. S. jacobaea is also an important species for insects in its introduced range (Frick, 1964; Frick and Hawkes, 1970; Frick, 1972).

Despite PA toxicity, S. jacobaea has been recommended for medicines (e.g. Gerard, 1597; Grieve, 1931; Schoental, 1963; Wren, 1968) and continues to be used in homeopathic preparations.

Anecdotal reports indicate that enterprising farmers may sell S. jacobaea as cut flowers to an unsuspecting public (Page, 1993).

Similarities to Other Species/Conditions

Top of page The morphological variability of S. jacobaea means that it may be confused with some of the other larger Senecio species and other Asteraceae. In Europe, the most likely sources of confusion are S. erucifolius, S. aquaticus and S. squalidus. S. erucifolius has a creeping rhizome, that forms small patches and clumps, and finely divided stem leaves with an acute terminal lobe, in contrast to the blunt terminal lobe of S. jacobaea leaves. Furthermore, disc and ray achenes of S. erucifolius are hairy. S. aquaticus can be difficult to separate from S. jacobaea, especially when the main stem of the latter has been destroyed. However, S. aquaticus has a loose, irregular-spreading corymb, large capitula (2.5 - 3 cm diameter), white-margined involucral bracts and both the ray and disc achenes being ±glabrous. Furthermore, S. aquaticus tends to be found in marshes, wet meadows and ditches and is more common in the northern part of the range of S. jacobaea. S. squalidus is distinguished from S. jacobaea by the loose, irregular-spreading corymb, short stature (20 - 40 cm) and its occurrence as a weed of waste places and walls; S. squalidus is very rarely found in grassland. At the early growth stages, S. jacobaea may be confused with S. sylvaticus, although the greenish-grey, gland-covered, strongly-scented leaves of S. sylvaticus are distinct from those of S. jacobaea. At the flowering stage, S. sylvaticus and S. jacobaea are distinct: S. sylvaticus is short (30 - 70 cm) and the capitula have indistinct ray florets.

In North America, based on the size of the plant, S. jacobaea may be confused with S. eremophilus and Tanacetum vulgare. S. jacobaea and S. eremophilus are distinguished by leaf morphology; leaves of S. eremophilus taper to a point and are once partite, whilst those of S. jacobaea are rounded and 2-3 partite. The homomorphic, discoid capitula, dark-margined phyllaries and strongly aromatic leaves of T. vulgare distinguish it from S. jacobaea.

In New Zealand, S. jacobaea may be confused with another exotic, S. aquaticus.

Prevention and Control

Top of page Cultural Control

Sheep will graze S. jacobaea at both the rosette and the flowering stages. Grazing at the rosette stage can weaken the plant and delay flowering, whilst at the flowering stage it can prevent achene production. Sheep show a high tolerance of pyrrolizidine alkaloids, particularly older sheep, and have been suggested as a means of controlling S. jacobaea (Brenchley, 1920; Sharrow and Mosher, 1982; Amor et al., 1983; Olson and Lacey, 1994; Betteridge et al., 2000). Heavy stocking is normally necessary to ensure that at least the larger rosettes and the flowering plants are grazed. However, continuous exposure of sheep to dense ragwort infestations should be avoided as toxicity problems can occur, particularly in areas known to have a high copper content in the soil (WHO, 1988). Following grazing, ragwort plants may recover quickly and produce new shoots. A second crop of flowers may be produced following grazing at the flowering stage, which will necessitate a further grazing if achene production is to be prevented. Sheep-based control of S. jacobaea cannot be recommended on animal welfare grounds.

Pasture improvement is as an essential adjunct to any control programme. Maintenance of a dense vigorous pasture will reduce the opportunity for S. jacobaea seedlings to establish and help to prevent the spread of S. jacobaea. Cropping pastures infested with S. jacobaea is one of the most effective ways of reducing the infestation. Repeated cultivation destroys the established plants and exhausts the achene banks in the soil.

Alternative land uses may be considered in cases of heavy infestations. Establishing trees for forestry or amenity purposes may provide an effective way of suppressing S. jacobaea as has been suggested in Tasmania, Australia (DPIWE, 1998). Such cultural control is a long-term intervention, therefore interim control measures are still essential.

Mechanical Control

Mechanical approaches to S. jacobaea control include cutting, digging-out, hand-pulling and machine-pulling; each of these treatments may need to be repeated two or three times per year (preferably before flowering). Cutting is a useful emergency treatment to prevent fruiting, although the plants must be cut before the achenes are mature and the treatment must be followed by another control treatment, since cutting may encourage production of side shoots. For pulling to be effective, the crown, together with the larger roots, must be completely removed from the ground or rapid regrowth may occur. Regrowth from the small roots that would normally be left after pulling or grubbing is also possible. Digging-out and hand-pulling (using gloves) are best accomplished when the soil is wet but are not practical for large areas of S. jacobaea infestation. A problem of both digging-out and hand-pulling control methods are that small plants may be missed, hence the need for annual treatment. Machine-pulling is suitable for large areas of infestation; plants are selected based on height differences; however, shorter plants are ignored. Plants must be removed from the site, as there is evidence that once removed from the soil, they show increased palatability to livestock, and burnt to prevent achene production.

Chemical Control

Many different herbicides, types of application methods and times of application have been tested in the UK, North America, Australia and New Zealand for the control of S. jacobaea. An important part of such investigations is the effect of the herbicide treatment on useful species in the pasture sward (such as Trifolium and Lolium species).

Herbicide type

Black (1976) showed that 2,4-D ester gave effective control of S. jacobaea in the late-rosette, bud and flowering stages, although repeated treatments were necessary. 2,4-D was superior to 2,4-DB at equivalent rates. 2,4-DB ester effectively controlled seedling and early-rosette S. jacobaea only. Furthermore, the herbicides mecoprop, 2,3,6-TBA, 2,4-D acid and fenoprop were as effective as 2,4-D ester for the control of S. jacobaea but caused more injury to other sward components. Thompson (1977) showed that granular application of picloram gave effective S. jacobaea control, followed by chlorthiamid, dichlobenil, 2,4-D and dicamba. Lawson and Wiseman (1982) found that clopyralid in a gel, applied in the spring, killed S. jacobaea. Rahman et al. (1990) showed that a combination of 2,4-D and phosphate fertilizer resulted in the best sward composition and growth, and allowed the least re-invasion of ragwort into low fertility hill country pasture. Friend (1987) showed that for complete prevention of achene production it was necessary to use a mixture of diquat and clopyralid or 2,4-D. Dixon and Clay (2001) showed that weed wiper applications of glyphosate and clopyralid applied in both May and June and glyphosate applied as a conventional spray in June (in the UK) killed all plants, whilst clopyralid appeared to reduce the number of plants germinating the following year. Dixon and Clay (2001) also showed that citronella oil (Cymbopogon winterianus) had a more rapid effect than either clopyralid or 2,4-D, especially when applied to smaller plants in March. Treatment of S. jacobaea with 2,4-D appears to mobilize carbohydrates and may make the plant more palatable to livestock (Irvine et al., 1977).

Application method

Bird (1977) demonstrated that a boom spray application of 2,4-D ester gave only 40% control of S. jacobaea, whereas a boom spray application combined with two spot sprays of picloram in September and November in New Zealand gave about 95% control. Thompson (1977) showed that as a foliar spray, asulam was less effective than any granular herbicide application, except dicamba. Spot applications of granules of picloram or dicamba completely killed old plants (Taylor, 1973). Martin et al. (1988) in trials in New Zealand showed that spot treatments of picloram with 2,4-D provided >95% control, regardless of application time. James et al. (1997) showed that spot treatment of flazasulfuron resulted in excellent weed control and avoided the problem of pasture damage. Friend (1987) reported that clopyralid, applied as a spot spray, at the late rosette and shooting stages completely prevented achene production and gave a very high level of mortality.

Time of application

Forbes (1978) showed that October spraying with 2,4-D amine MCPA gave 99% control of S. jacobaea in Scotland. In Northern Ireland, Courtney (1975) reported that MCPA and 2,4-D gave 100% selective control in grassland when applied in spring. Herbicides may be applied over a wide range of dates between April and November, although spraying after the early bud stage may allow achenes to be produced. Forbes (1974) showed that MCPA, applied at the rosette stage in mid-May prevented flowering in the year of spraying. However, 2,4-D ester controlled both flowering and first year plants in the year of spraying better than MCPA. Friend (1987) found that no achenes were produced when plants were sprayed with clopyralid before the appearance of the first flowers, although achene weight and germinability increased when spraying was delayed until after flowering. In Australia, there is evidence that regrowth and flowering may occur in 2,4-D-treated plants but the achenes are infertile (Watt, 1987).

Effect on other pasture species

Black (1976) showed grasses and white clover were increasingly injured as 2,4-D ester application increased. Taylor (1973) showed that overall application of herbicides frequently resulted in severe damage to white clover (Trifolium repens). James et al. (1997) achieved very good weed control with flazasulfuron but also damage to the pasture, particularly Lolium perenne.

In general, 2,4-D is a successful control agent, although a second application is often needed for adequate control and older plants need higher doses than generally recommended. In the UK, spraying as late as December increased subsequent germination and establishment of seedlings compared with an April application, although this would not be a problem for annual herbicide application (Forbes, 1978). DEFRA (2002) recommend herbicide applications (2,4-D or citronella oil for selective control and glyphosate for non-selective control) when rosettes start growing or in early summer before flower heads mature, using either spot-treatment, a wick applicator or spraying with a selective herbicide. In any of these cases, herbicide may need to be applied twice per year, every two years. Other recommendations for chemical control of S. jacobaea in parts of its introduced range can be found (e.g., DPIWE, 1998).

Biological Control

Biological control is effective in reducing plant density and is recommended for areas where other controls are neither practical nor economical. Several years are required to establish an insect population large enough to reduce a weed population. The objective is not to eradicate S. jacobaea but to reduce it to a level where it has negligible economic effects. The three most frequently introduced insects for biological control are Tyria jacobaeae (cinnabar moth), Longitarsus jacobaeae (ragwort flea beetle) and Botanophila seneciella (ragwort seed fly). T. jacobaeae larvae feed on the aerial parts of S. jacobaea (Dempster, 1982; James et al., 1992). B. seneciella larvae penetrate the achene heads and feed on the developing achenes, usually attacking up to 40% of the heads and consuming 75-95% of the achenes (McEvoy et al., 1991); uneaten achenes often fail to germinate. L. jacobaeae larvae feed on the root crowns, stems and leaf petioles of the plants, whilst adults attack the leaves (Frick, 1970; Hawkes and Johnson, 1978; Windig, 1991).

Reviews of biological control strategies for S. jacobaea have been prepared for its introduced distribution, particularly for North America (e.g., McEvoy et al., 1991), Australia (e.g., McLaren et al., 2000) and New Zealand (e.g., Syrett, 1983). The success of such strategies have been mixed, for example, they have been very valuable in controlling S. jacobaea in California and Oregon ( Pemberton and Turner, 1990; McEvoy et al., 1991), Canada (Harris et al., 1979) and Tasmania (McLaren et al., 2000) but, to date, have proven less useful in New Zealand (Ivens, 1979; Syrett et al., 1991). Biological control does not appear to be an effective strategy for S. jacobaea control in the UK (Clay et al., 2000).

S. jacobaea was brought under successful biological control in California through the combined action of T. jacobaeae and L. jacobaeae, which persist despite very low S. jacobaea densities (Pemberton and Turner, 1990). The control of S. jacobaea has resulted in the return of nearly natural vegetation on coastal prairie sites and improved productivity on pasture sites (Pemberton and Turner, 1990). T. jacobaeae was released in western parts of North America during 1959-1962 for S. jacobaea control (Nagel and Isaacson, 1974) and together with additional releases of T. jacobaeae, L. jacobaeae and B. seneciella in western Oregon in 1975, has resulted in the reduction of S. jacobaea infestations by 60-70% (Brown, 1990).

T. jacobaeae and L. jacobaeae are complementary enemies of S. jacobaea and feed on different stages and at different times of the year (Crawley and Pattrasudhi, 1988), and have proved an effective biocontrol strategy in North America, although in coastal areas of North America, L. jacobaeae appears to be the main control factor (e.g. Harris et al., 1981; Hawkes, 1981; McEvoy et al., 1991; Syrett et al., 1991; James et al., 1992). Ireson et al. (2000) showed that Longitarsus flavicornis was dispersed over all infested areas of southern Tasmania, and more than 90% of northern Tasmania. However, prevailing site conditions (e.g. flooding) and incompatible management practices (e.g. boom-sprayed herbicides) restrict the efficacy of L. flavicornis on many areas of Tasmania. Recently, the lepidopteran Cochylis atricapitana, the larvae of which are leaf, crown, stem or bud borers, has been effective in controlling S. jacobaea in Australia (McLaren, 1992; McLaren, 2000), especially where T. jacobaeae and B. jacobaeae have not proven particularly effective (Field, 1990; Syrett, 1990).

Much research has been undertaken into the biological relationships between S. jacobaea and its insect pests in both its native (e.g., Islam and Crawley, 1983; Crawley and Nachapong, 1984; Wilcox and Crawley, 1988; Crawley and Gillman, 1989; Gillman and Crawley, 1990) and introduced ranges (e.g., McEvoy et al., 1991; McEvoy et al., 1993; McEvoy and Rudd, 1993; McEvoy and Coombs, 1999).

Integrated Control

Thousands of pages on the Web are devoted to S. jacobaea control, particularly in North America, Australia and New Zealand. These pages, and particularly those of Government agencies, should be consulted for the most recent recommendations regarding S. jacobaea control. In addition, Government agencies have produced information leaflets on the control of S. jacobaea where it is, or is likely to become, a problem (e.g., Northland Regional Council, undated; Mather, undated; MAFF, undated). Integrated management requires containment, reduction and finally elimination of S. jacobaea. Such long-term control has a short-term goal of preventing achene production in infested areas, and is emphasized by all control recommendations. In general, S. jacobaea occurrence in pastures is a symptom of poor management, therefore reseeding and grazing and fertility management may be essential components of a control plan. Furthermore, if management is to be effective in pastures, control must also take place on wasteland, set-aside and roadsides (DEFRA, 2002). Woo et al. (2001) discuss the integrated management of S. jacobaea.


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