Carduus nutans (nodding thistle)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Plant Type
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Biology and Ecology
- Latitude/Altitude Ranges
- Air Temperature
- Rainfall Regime
- Soil Tolerances
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Pathway Vectors
- Plant Trade
- Impact Summary
- Impact: Biodiversity
- Threatened Species
- Social Impact
- Risk and Impact Factors
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Carduus nutans L.
Preferred Common Name
- nodding thistle
Other Scientific Names
- Carduus macrocephalus Desf.
- Carduus thoermeri Weinm.
International Common Names
- English: musk thistle
- Spanish: cardo almizclero; cardo pendiente; cardo rojo
- French: chardon nu; chardon penche
Local Common Names
- Germany: Nickende Distel
- Italy: cardo rosso
- Netherlands: knikkende Distel
- Sweden: nicktistel
- CRUMA (Carduus macrocephalus)
- CRUNU (Carduus nutans)
- CRUTH (Carduus thoermeri)
Summary of InvasivenessTop of page It is considered a serious pasture weed in parts of New Zealand, Australia, USA, Canada and Argentina. It can also create some problems in arable crops and seed crops in all of these countries. The aggressive growth and rapid spread of C. nutans that has occurred in pastoral systems show that this species is capable of being very invasive if allowed to invade. Pastures that are subjected to fertilizers and over-grazing are particularly vulnerable, especially in temperate climates with rainfall between 500-1000 mm. It has been declared noxious in most countries where introduced to help curb further spread.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Asterales
- Family: Asteraceae
- Genus: Carduus
- Species: Carduus nutans
Notes on Taxonomy and NomenclatureTop of page Carduus is the Latin name for 'thistle' and nutans is Latin for 'nodding', referring to the drooping attitude of the mature flower heads (Popay and Medd, 1990). There is considerable variation within this species, and confusion still exists as to what rank to assign to variant populations. Within Europe where the species originated, Franco (1976) described seven other large-flowered Carduus species alongside C. nutans. However, he felt these taxa needed further study due to considerable variation within the group that made differentiation between the species difficult. Of these species, McCarty (1985) considered three of them to be present within North America, namely C. nutans, C. thoermeri and C. macrocephalus, but suggested that the similarity between the taxa meant they should be assigned to subspp. of C. nutans. Desrochers et al. (1988a) conducted a biosystematic study of the complex, including morphological, flavonoid and isozyme analyses. They concluded that these taxa within North America can be best described as one species with two subspecies, namely C. nutans subsp. nutans and subsp. leiophyllus (Petrovic) Stoj. & Stef. Plants within Australia and New Zealand appear to also belong to these two taxa, with most being C. nutans subsp. nutans (Popay and Medd, 1990). Due to the general confusion within the literature as to exactly which sub-species of C. nutans was present within each trial reported, no attempt will be made to separate out the subspecies within the present review.
DescriptionTop of page Popay and Medd (1990) provided the following description of C. nutans. It is an annual, or usually biennial herb initially forming a prostrate rosette. Cotyledons are nearly sessile, rather oblong in shape, often squarish tipped. The first true leaves are more or less opposite; develop simultaneously up to 2.5 cm long with soft-prickly teeth and some multi-cellular hairs. Very young rosettes are open, consisting of relatively undissected leaves bearing soft spines on the margins and sometimes with a few simple hairs on the upper surface. Young leaves are relatively soft and upright, especially in long grass or among other thistle seedlings. After three to five true leaves have formed, they become harder, spinier and pressed to the ground, forming a flattened rosette. Older rosette leaves are pinnatifid and undulating. Lobes are palmate or triangular, with prominently spined margins. Mature leaves often have a faint metallic sheen, and a whitish marginal zone, especially about the bases of the leaves. The rosettes have stout, sometimes branched, taproots which penetrate to 40 cm or more, helping to make them more tolerant of drought than many other pasture species.
The reproductive phase begins when the apex of the rosette elongates ('bolts') after vernalization, with some rosette leaves being carried up on the stem while the remainder die. An erect branched stem up to 150 cm tall rapidly forms. Damage to the apex may result in the formation of several stems. The stems are woolly, spinous-winged, with peduncles naked for a variable distance below the head. Solitary terminal capitula form first on the main stems then successively on lower branches. The emerging buds are upright initially then drooping distinctively at right angles or more to the stem at maturity. Flower heads are woolly, up to 6 cm in diameter, surrounded by several whorls of spiny tipped, often purplish phyllaries. The outer ones reflex at maturity, and phyllaries of intermediate whorls are constricted in the middle, with bases broader than the blades. The corolla is bright crimson or crimson-purple in colour, rarely white. Achenes are 3.0-4.5 mm long, fawn, with fine transverse wrinkles. Pappus consists of numerous simple white hairs are up to 2 cm long.
Desrochers et al. (1988a) state that C. nutans subsp. nutans have phyllaries with arachnoid hairs and which have their lower portions equal or slightly narrower than their upper portions. The leaves are moderately to densely pubescent and the flower head is 1.5-3.5 cm in diameter. The achene is 3.2-3.8 mm long. In contrast, C. nutans subsp. leiophyllus have glabrous phyllaries with their lower portions definitely narrower than their upper portions. The leaves are glabrous to slightly pubescent and flower heads with diameters of 1.8-4.5 cm (sometimes to 7 cm). Achenes are 4.0-5.0 mm long.
Plant TypeTop of page Annual
Distribution TableTop of page
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/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|China||Restricted distribution||Invasive||Ichizen et al., 1993|
|-Nei Menggu||Present||Liu et al., 2003|
|-Xinjiang||Present||Native||Flora of China Editorial Committee, 2003; USDA-ARS, 2003|
|Georgia (Republic of)||Present||Native||Missouri Botanical Garden, 2003; USDA-ARS, 2003|
|Iran||Present||Native||Not invasive||Holm et al., 1979|
|Kyrgyzstan||Present||Native||Missouri Botanical Garden, 2003; USDA-ARS, 2003|
|Turkey||Widespread||Native||Invasive||Holm et al., 1979|
|Tunisia||Present||Native||Not invasive||Medd and Smith, 1978|
|Canada||Present||Present based on regional distribution.|
|-Alberta||Restricted distribution||Introduced||Invasive||Desrochers et al., 1988b|
|-British Columbia||Restricted distribution||Introduced||Invasive||Desrochers et al., 1988b|
|-Manitoba||Widespread||Introduced||Invasive||Desrochers et al., 1988b|
|-New Brunswick||Widespread||Introduced||1871||Invasive||Desrochers et al., 1988b|
|-Newfoundland and Labrador||Restricted distribution||Introduced||Invasive||Desrochers et al., 1988b|
|-Ontario||Widespread||Introduced||1920||Invasive||Desrochers et al., 1988b|
|-Quebec||Present||Introduced||Royal Botanical Gardens Canada, 2003|
|-Saskatchewan||Widespread||Introduced||Invasive||Desrochers et al., 1988b|
|USA||Present||Present based on regional distribution.|
|-Alabama||Restricted distribution||Introduced||Invasive||Dunn, 1976|
|-Arizona||Present, few occurrences||Introduced||Invasive||Dunn, 1976|
|-Delaware||Present, few occurrences||Introduced||Invasive||Dunn, 1976|
|-Massachusetts||Present, few occurrences||Introduced||Invasive||Dunn, 1976|
|-Mississippi||Present, few occurrences||Introduced||Invasive||Dunn, 1976|
|-Nevada||Restricted distribution||Introduced||Invasive||Dunn, 1976|
|-New Hampshire||Present||Introduced||Invasive||USDA-NRCS, 2002|
|-New Jersey||Restricted distribution||Introduced||1853||Invasive||Dunn, 1976|
|-New Mexico||Present, few occurrences||Introduced||1853||Invasive||Dunn, 1976|
|-New York||Present, few occurrences||Introduced||1853||Invasive||Dunn, 1976|
|-North Carolina||Present, few occurrences||Introduced||Invasive||Dunn, 1976|
|-North Dakota||Widespread||Introduced||Invasive||Dunn, 1976|
|-Ohio||Restricted distribution||Introduced||Invasive||Dunn, 1976|
|-Oregon||Restricted distribution||Introduced||Invasive||Dunn, 1976|
|-Pennsylvania||Restricted distribution||Introduced||Invasive||Dunn, 1976|
|-Rhode Island||Present||Introduced||Invasive||USDA-NRCS, 2002|
|-South Carolina||Restricted distribution||Introduced||Invasive||Dunn, 1976|
|-South Dakota||Widespread||Introduced||Invasive||Dunn, 1976|
|-Texas||Present, few occurrences||Introduced||Invasive||Dunn, 1976|
|-Washington||Restricted distribution||Introduced||Invasive||Dunn, 1976|
|-West Virginia||Widespread||Introduced||Invasive||Dunn, 1976|
|Argentina||Present||Introduced||1920s||Invasive||Holm et al., 1979|
|Uruguay||Restricted distribution||Introduced||Invasive||Holm et al., 1979|
|Austria||Widespread||Native||Invasive||Holm et al., 1979|
|Belgium||Present||Native||Not invasive||Royal Botanic Garden Edinburgh, 2003|
|Czech Republic||Present||Native||Not invasive||Royal Botanic Garden Edinburgh, 2003|
|Finland||Present||Native||Not invasive||Medd and Smith, 1978|
|France||Present||Native||Not invasive||Holm et al., 1979|
|Germany||Widespread||Native||Invasive||Holm et al., 1979|
|Hungary||Widespread||Native||Invasive||Holm et al., 1979|
|Italy||Present, few occurrences||Native||Not invasive||Holm et al., 1979|
|Moldova||Present||Native||Not invasive||Royal Botanic Garden Edinburgh, 2003|
|Netherlands||Present||Native||Not invasive||Royal Botanic Garden Edinburgh, 2003|
|Norway||Present||Native||Not invasive||Medd and Smith, 1978|
|Poland||Widespread||Native||Invasive||Holm et al., 1979|
|Russian Federation||Widespread||Native||Invasive||Holm et al., 1979|
|-Central Russia||Present||Native||USDA-ARS, 2003|
|-Northern Russia||Present||Native||USDA-ARS, 2003|
|-Southern Russia||Present||Native||Not invasive||Royal Botanic Garden Edinburgh, 2003|
|Serbia||Present||Native||Not invasive||Holm et al., 1979|
|Slovakia||Present||Native||Not invasive||Royal Botanic Garden Edinburgh, 2003|
|Spain||Present||Native||Royal Botanic Garden Edinburgh, 2003|
|Sweden||Present||Native||Not invasive||Medd and Smith, 1978|
|Switzerland||Present||Native||Not invasive||Medd and Smith, 1978|
|UK||Widespread||Native||Not invasive||Perring, 2002|
|Ukraine||Present||Native||Not invasive||Royal Botanic Garden Edinburgh, 2003|
|Australia||Present||Present based on regional distribution.|
|-New South Wales||Widespread||Introduced||1950||Invasive||Medd, 1987|
|-Queensland||Restricted distribution||Introduced||Invasive||Doing et al., 1969|
|-South Australia||Eradicated||Introduced||Invasive||Medd, 1987|
|-Tasmania||Restricted distribution||Introduced||Invasive||Medd, 1987|
|-Victoria||Present, few occurrences||Introduced||Invasive||Medd, 1987|
|-Western Australia||Eradicated||Introduced||Invasive||Medd, 1987|
|New Zealand||Widespread||Introduced||1889||Invasive||Webb et al., 1988|
History of Introduction and SpreadTop of page C. nutans is thought to have first arrived in the USA in 1853 within ship's ballast dumped at Camden, New Jersey (Dunn, 1976). Other sightings of the weed were made in eastern North America (from New Brunswick, Canada to New York and Pennsylvania, USA) between 1853 to 1882. From these scattered infestations, the weed has spread through USA and Canada, probably in farm seed and hay (Desrochers et al., 1988b). It is recorded as reaching Otago, New Zealand in 1889 (Popay and Medd, 1990) and has since spread to other parts of the country, probably also in pasture seed and hay. It was first introduced from New Zealand to Australia in 1950 as a contaminant within pea (Pisum sativum) seed (Medd, 1987), though has probably been introduced many times in different lots of seeds imported into Australia, both from New Zealand and the United Kingdom (Doing et al., 1969). C. nutans was reported by Doing et al. (1969) as being well established in Argentina in the 1920s.
Risk of IntroductionTop of page Due to tightening regulations concerning the movement of weed seeds with crop seeds, this pathway is now less likely than in the past. However, uncertified seed is still transported within countries and occasionally between countries. Movement with hay is the other main pathway for long-distance dispersal within countries.
HabitatTop of page C. nutans occurs naturally in a wide range of climates in Europe, Asia Minor and North Africa (Popay and Medd, 1990). Within its native range in Britain, it is considered to be a weed of rough, often overgrazed or recently established pastures, on roadsides and disturbed places, mainly on chalk, limestone or limestone-enriched soils, and also sandy or shingly ground (Perring, 2002). In Italy, it is usually found in loamy-sand soil of marginal productivity that has been disturbed by man or animals (Boldt, 1978). It has since spread to improved grasslands in parts of Canada, USA, Australia and New Zealand, where it does best if soil fertility is good, winters are cool but autumn and spring are warm and moist (Popay and Medd, 1990). Doing et al. (1969) have found C. nutans thrives if soils are deep, well drained and lack compacted horizons, have high nitrogen and especially phosphate levels, and high exchangeable calcium. Dry summers assist the species by causing poor pasture cover in autumn when rains arrive, allowing seedlings to establish while competition is minimal (Popay and Medd, 1990). C. nutans is typically found in pastures grazed by sheep rather than cattle because of the tighter grazing of pastures by sheep reducing competition with emerging thistle seedlings (Harrington, 1996). Although often most troublesome in grasslands, C. nutans is also a weed in habitats where soil is disturbed, such as cultivated fields (Letendre et al., 1976), roadsides and field nurseries (Monks et al., 1991). In Europe, occurrence is generally in deciduous hardwood and not in coniferous climax zones.
Habitat ListTop of page
|Terrestrial – Managed||Cultivated / agricultural land||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|
|Terrestrial ‑ Natural / Semi-natural||Natural grasslands||Present, no further details||Harmful (pest or invasive)|
|Riverbanks||Present, no further details|
Hosts/Species AffectedTop of page Although C. nutans is sometimes found in crops, it is primarily a weed of grasslands. The species involved depend on the composition of the pastures found in each of the countries that the weed is a problem. For example, it is associated with phalaris (Phalaris aquatica)/ white clover (Trifolium repens) pastures in Australia (Medd, 1979) and perennial ryegrass (Lolium perenne)/ white clover pastures in New Zealand (Panetta and Wardle, 1992). In Argentina, C. nutans is considered a weed in alfalfa (Medicago sativa L.) and cereal crops (Doing et al., 1969).
Host Plants and Other Plants AffectedTop of page
Biology and EcologyTop of page Genetics
The chromosome number for C. nutans is 2n=16 (Moore and Mulligan, 1956). This species hybridizes readily with C. acanthoides, which has 2n=22. The chromosome numbers of the hybrids have been shown by Moore and Mulligan (1956) to be continuous between 16 and 22, with F1 hybrids having a number intermediate between the two parents. The morphological traits of the various intermediate hybrids and backcrosses have been studied by Warwick et al. (1992).
Physiology and Phenology
The seeds of C. nutans show innate dormancy during the first few months after being released into the soil, but this usually disappears within 4 months (Popay et al., 1987). Seeds normally germinate soon after innate dormancy is over, usually during autumn, while pasture grasses offer little competition following damage by summer dryness (Popay and Thompson, 1979). Germination is greatest at temperatures of 15-30°C and when soil is moist (Popay and Medd, 1990). Germination is inhibited by far-red light and is stimulated by white or red light, potassium nitrate or pricking the seed coat (Medd and Lovett, 1978a). Thus a pasture cover 6-7 cm high can reduce C. nutans germination by 90% (Phung and Popay, 1981), and also cause high mortality of seedlings that do germinate. Only 8.3% (1-19%) survival was observed in autumn-germinated C. nutans in New Zealand pastures.
C. nutans are normally biennial, flowering in the second summer following an autumn germination (Popay and Medd, 1990). C. nutans has an absolute low temperature vernalization requirement for floral initiation, though older, bigger plants need shorter periods of vernalization than younger ones (Medd and Lovett, 1978b). Thus plants can act as winter annuals if growing conditions allow rapid growth over winter, and the time of year that seedlings establish is also important. Interference with its normal development, such as grazing or spraying, can cause the species to act as a short-lived perennial (Doing et al., 1969), making control difficult when plants of different ages are present.
The compound capitulum of C. nutans consists of tubular florets, with each floret bearing male and female organs, and fertilization is mostly through out-crossing (Popay and Medd, 1990). The style transports previously discharged sticky pollen grains from the anther cylinder as it elongates. Stylar branches later bifurcate, exposing the inner receptive surfaces to pollen. Florets progressively mature inwardly from the periphery of the capitula. These asynchronous development events result in autogamous, geitonogamous and xenogamous pollination, generally effected by a wide range of short and long-tongued insects feeding on nectar secreted into the corolla tube by a ridge surrounding the base of the style. The sticky nature of the pollen prevents wind-dispersal.
Propagation is completely by seeds, which are produced principally over an 11-week period each summer. An average of 63 seed-bearing inflorescences were produced per plant in New Zealand, resulting in 6200 viable seeds per plant (Jessep, 1990). Popay et al. (1984) estimated under pasture conditions that seed production would average 8622 per m² (65% viability) from 3.8 flowering stems per m² carrying 29 flower heads per m². If seeds remain ungerminated on the soil surface, they seldom survive longer than 1-2 years, whereas James et al. (1998) have estimated seeds buried 20 cm deep will last 80 years or longer. They found that after 16 years of burial, seeds 5 cm deep still exhibited 20% viability and those at 20 cm had 32% viability.
Medd and Smith (1978) attempted to predict the climatic limits for the spread of C. nutans within Australia, and noted how it is adapted to a wide range of climates in Europe, including Mediterranean, temperate and maritime climates. Frosts during summer flowering are assumed to limit its growth in cooler climates, and a vernalization requirement prevents it from flowering in areas with warm winters (Medd and Lovett, 1978b). Doing et al. (1969) states that C. nutans spread markedly in Australia during a sequence of wet years, whereas in more humid New Zealand climates, spread was hastened by a series of dry summers. Dryness is required to allow pastures to open up sufficiently for seedlings to establish successfully, but some moisture is required during the summer of flowering to maximize seed production (Popay and Medd, 1990). In Europe, it grows from sea level at the Baltic Sea to 2000 m altitude, but rarely over 1000 m in the Alps (Doing et al., 1969).
Doing et al. (1969) list species often associated with C. nutans in Europe and Australia where it is considered a pioneer species in disturbed environments with weakly differentiated soil profiles enriched in nitrogen. It is considered a characteristic species of the alliance Onopordion acanthii, occurring with high constancy in stands belonging to this vegetation unit, but rarely in large numbers. Some species listed both in Europe and Australia which frequently dominate in association with C. nutans include Conyza canadensis, Diplotaxis tenuifolia, Echium vulgare, Oenothera biennis, Reseda lutea and Senecio jacobaea. Popay and Medd (1990) consider C. nutans to be associated in Australia with annual communities maintained under grazing, dominated by Bromus spp., Hordeum leporinum, Malva neglecta, Medicago arabica, Modiola caroliniana and Trifolium subterraneum. In New Zealand, they list common associates as Hordeum murinum, H. leporinum, Lolium perenne, Trifolium repens, T. subterraneum and annual species of Trifolium and Medicago.
Latitude/Altitude RangesTop of page
|Latitude North (°N)||Latitude South (°S)||Altitude Lower (m)||Altitude Upper (m)|
Air TemperatureTop of page
|Parameter||Lower limit||Upper limit|
|Mean annual temperature (ºC)||7||23|
RainfallTop of page
|Parameter||Lower limit||Upper limit||Description|
|Dry season duration||0||6||number of consecutive months with <40 mm rainfall|
|Mean annual rainfall||250||1500||mm; lower/upper limits|
Rainfall RegimeTop of page Winter
Soil TolerancesTop of page
Special soil tolerances
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
|Cheilosia grossa||Herbivore||Growing point/Inflorescence/Roots/Stems|
|Trichosirocalus horridus||Herbivore||New Zealand|
|Urophora solstitialis||Herbivore||Inflorescence||New South Wales; Australia|
Notes on Natural EnemiesTop of page In the quest for suitable biological control agents for C. nutans, large numbers of natural enemies for this species have been identified (e.g. Desrochers et al., 1988b; Talosi et al., 1989; Gassmann and Kok, 2002), and the principal species are listed. All come from Europe, though some have already been introduced to other parts of the world as part of biological control programmes. Rhinocyllus conicus (Coleoptera: Curculionidae) lays eggs on flower bracts of C. nutans from where larvae burrow into the receptacle and reduce seed production due to their feeding behaviour within the receptacle (Hodgson and Rees, 1976). Trichosirocalus horridus (syn. Ceuthorhynchidius horridus) (Coleoptera: Curculionidae) lays its eggs on the underside of rosette leaves, from where the larvae feed on the leaf petiole and move down to the root/stem junction, often causing considerable damage to the rosette (Woodburn, 1997). Urophora solstitialis (Diptera: Tephritidae) complements the damage caused by R. conicus to seed production of C. nutans both in Europe and in other countries to which it has been introduced (Woodburn and Briese, 1996). Feeding of the larvae within the capitulum results in the formation of galls around the larvae, which reduces assimilates reaching the seeds. Cheilosia corydon (= C. grossa) (Diptera: Syrphidae) larvae feed inside the foliage and stems of C. nutans, which disrupts flower and seed production. Some attempts have been made to introduce this to USA from Italy (Quattro and Quattro, 1997). Puccinia carduorum (Uridenales: Pucciniaceae) is an autoecious rust fungus native to the Mediterranean area but is also reported from Bulgaria and Romania. The disease appears first as tiny yellow specks and in several days, rust pustules containing thousands of spores become visible. It was introduced accidentally to USA, where it is spreading and appears to only build up damaging levels on C. nutans and some other Carduus species (Bruckart et al., 1996). Ceutorhynchus trimaculatus (Coleoptera: Curculionidae) larvae feed on leaf buds, growing tips and in the crown of the rosette, and the adults also feed on C. nutans foliage. It was found to be one of the more damaging insects on C. nutans growing in southern Europe (Sheppard et al., 1995) but is not host-specific enough to be considered worth releasing in USA (Kok et al., 1982). Psylliodes chalcomera (Coleoptera: Chrysomelidae) is a flea beetle whose larvae feed on leaf buds and young rosette leaves, and adults also feed heavily on C. nutans (Gassmann and Kok, 2002). Trials have suggested this species is fairly host specific, with no damage occurring to Cirsium species in the USA, so some releases in USA were made in the late 1990s.
Means of Movement and DispersalTop of page Natural Dispersal (Non-Biotic)
C. nutans is generally considered to be dispersed by wind because of the pappus attached to ripe seed although it appears that seeds seldom travel far by this mechanism. Smith and Kok (1984) found that most seeds travelled no further than 50 m from the point of release and less than 1% were blown further than 100 m as they were detached from the pappus soon after leaving the mother plant.
Vector Transmission (Biotic)
As many animals prefer not to graze thistles, seeds are usually not dispersed in the guts of livestock. Goats do eat the seed heads however, but Holst and Allan (1996) showed that only 0.2% of C. nutans seed survive passage through a goat, and only 0.01% of these seeds germinated. Dispersal by animals is much more likely to occur from seed heads still containing seeds becoming attached to the fleeces of passing sheep. Pemberton and Irving (1990) consider the structure of C. nutans achenes make them very suited for dispersal by ants.
Most long-distance dispersal of C. nutans, within but especially between countries, is likely to have occurred due to contamination of pasture and crop seed, though this is now greatly reduced due to tightening regulations on seed quality (Popay and Medd, 1990). Some movement is also likely with seed contamination in hay, in lime for increasing soil pH, and on agricultural machinery.
Most if not all movements of C. nutans to new countries have been accidental, mainly in crop seed, but also possibly in ship ballast and hay (Desrochers et al., 1988b; Popay and Medd, 1990).
Pathway VectorsTop of page
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Fruits (inc. pods)||seeds|
|Growing medium accompanying plants||seeds|
|True seeds (inc. grain)||seeds|
|Plant parts not known to carry the pest in trade/transport|
|Stems (above ground)/Shoots/Trunks/Branches|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
ImpactTop of page The main economic impact of C. nutans is in pastures where it reduces animal production by preventing animals from eating plants growing in the vicinity of the plant and by suppressing the growth of desirable vegetation (Desrochers et al., 1988b). In addition to competition with pasture plants, there is some evidence that the weed may have an allelopathic effect (Wardle et al., 1991). Dense, mature stands of C. nutans become obstructive to livestock and dried fragments and spines may cause physical injury or adhere to wool, lowering its value (Popay and Medd, 1990). A simulation model studying the effects of C. nutans on pasture losses and animal production suggested it was economically beneficial to apply herbicides in spring whenever ground cover exceeded 2.5% (Moore et al., 1989). Apart from effects on animal production, many millions of dollars are spent annually on controlling C. nutans, primarily because of its status as a noxious plant (Vere and Medd, 1979). It is considered a serious pasture weed in parts of New Zealand, Australia, USA, Canada and Argentina. It can also create some problems in arable crops and seed crops in all of these countries.
Impact: BiodiversityTop of page It is generally only a problem in improved pastures subjected to fertilizers and heavy grazing pressure, rather than in natural plant communities. Care is required in North America not to introduce biological control agents that might impact on native thistle species (Gassmann and Kok, 2002).
Threatened SpeciesTop of page
|Threatened Species||Conservation Status||Where Threatened||Mechanism||References||Notes|
|Astragalus schmolliae (Schmoll's milkvetch)||CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered); NatureServe NatureServe; USA ESA candidate species USA ESA candidate species||Colorado||Ecosystem change / habitat alteration||US Fish and Wildlife Service, 2015a|
|Centrocercus minimus (Gunnison sage-grouse)||USA ESA listing as threatened species USA ESA listing as threatened species||Colorado; Utah||Ecosystem change / habitat alteration||US Fish and Wildlife Service, 2013|
|Cirsium vinaceum (Sacramento Mountains thistle)||NatureServe NatureServe; USA ESA listing as threatened species USA ESA listing as threatened species||New Mexico||Competition (unspecified); Ecosystem change / habitat alteration||US Fish and Wildlife Service, 2010|
|Cirsium wrightii (Wright's marsh thistle)||NatureServe NatureServe; USA ESA candidate species USA ESA candidate species||Arizona; New Mexico||Competition (unspecified); Ecosystem change / habitat alteration||US Fish and Wildlife Service, 2015b|
Social ImpactTop of page Heavy infestations probably reduce the value of pastoral properties.
Risk and Impact FactorsTop 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
- Ecosystem change/ habitat alteration
- Negatively impacts agriculture
- Negatively impacts animal health
- Negatively impacts tourism
- Reduced amenity values
- Threat to/ loss of endangered species
- Threat to/ loss of native species
- Competition - monopolizing resources
- Produces spines, thorns or burrs
- Highly likely to be transported internationally accidentally
UsesTop of page Although C. nutans is generally considered to have no uses, high quality honey is made from its flowers (Popay and Medd, 1990). Aktay et al. (2000) report that it is used in Turkish folk remedies.
Similarities to Other Species/ConditionsTop of page Given that Desrochers et al (1988a) consider most of the large headed Carduus thistles outside of the native range of these species are probably subspecies of C. nutans, the main weedy species likely to be confused with C. nutans is Carduus acanthoides L. This species, known as plumeless thistle, is sufficiently similar to C. nutans that hybrids of the two species commonly form where they grow together in Canada (Moore and Mulligan, 1956), USA (Dunn, 1976) and New Zealand (Webb et al., 1988). Moore and Mulligan (1956) describe C. nutans as having flower heads mostly 2.5-4.0 cm diameter, nodding and tending to be solitary, compared with 1.5-2.5 cm diameter heads in C. acanthoides which are erect and tend to be clustered. Stems in C. nutans are without spiny wings below the head but are spiny-winged up to the head in C. acanthoides. Hybrids have an intermediate morphology.
Prevention and ControlTop of page Cultural Control
As C. nutans is a biennial found mainly in pastures, a key to controlling it in such systems is to utilize its dormancy when covered by green vegetation, preventing it from germinating (Phung and Popay, 1981). Techniques to utilize this include sowing pastures in dry areas with drought-tolerant cultivars and avoiding overgrazing of pastures during dry times of the year by reducing stock numbers and growing supplementary crops (Harrington, 1996). Although sheep and cattle avoid grazing C. nutans plants, goats will graze them especially as seed-heads are forming (Holst and Allan, 1996). C. nutans is still spreading to new areas and increasing its density in presently infested areas. Declaring the species noxious and thus applying regulatory pressures to reduce its incidence is a common strategy for controlling the species (Skinner et al., 2000). Prohibiting the presence of any C. nutans seed within certified pasture and crop seed is a common strategy to reduce further spread of the species (Popay and Medd, 1990).
Hand grubbing is commonly practised for infestations of low density or as a follow-up operation after herbicide treatment of denser or larger infestations (Popay and Medd, 1990). Grubbing hoes must cut the plants 5-10 cm below ground level to prevent resprouting from dormant axillary buds. Mowing the plant during flowering can greatly reduce seed production, though a single mowing is seldom sufficient due to the wide differences in the maturity of plants in a natural population (McCarty and Hatting, 1975).
Good control of C. nutans can be obtained using herbicides such as 2,4-D, MCPA, clopyralid, dicamba and picloram, though the favoured option in clover-based pastures is to use the less effective MCPB while seedlings are young and thus susceptible to this herbicide (Popay and Medd, 1990). MCPA or 2,4-D will successfully control larger rosettes without damaging the clover substantially, but application must occur before rosettes become too large, and plants need to be actively growing (Popay et al., 1989). Repeated application of phenoxy herbicides to C. nutans populations over several decades has led to resistant ecotypes developing in some parts of New Zealand (Harrington, 1990).
Of the organisms listed in the Natural Enemies section, some have been introduced widely throughout the world to control C. nutans whereas others have been only tentatively released thus far and several have been deemed unsuitable for use.
Rhinocyllus conicus has been released in Canada, USA, New Zealand and Australia since the 1970s and is well established in all of these countries (Popay and Medd, 1990). Although R. conicus has been recorded as being successful against C. nutans in parts of the USA, it has generally been less successful in New Zealand where it has been estimated that 69% reduction in seed production is required to reduce C. nutans populations, more than is usually achieved by the weevil (Shea and Kelly, 1998).
Trichosirocalus mortadelo is probably restricted to C. nutans, and was introduced from Germany to Canada and from there to New Zealand and then Australia, and from Italy to the USA. However, it remains a possibility that the original introductions for C. nutans also included T. horridus and examination of voucher specimens is required to clarify the issue (Julien and Griffiths, 1998). Cartwright and Kok (1985) found the response of C. nutans in the USA was dependent on plant size and growing conditions, though infested plants consistently produced more stems and larger crowns than uninfested individuals due to the destruction of apical dominance. However, small and medium infested plants were shorter and produced fewer seeds and heads than uninfested plants. In Australia, Woodburn (1997) found T. horridus killed some plants and reduced rosette growth of survivors by 50%. The reproductive potential of the attacked plants, measured as seeds per plant, was reduced by 67%.
The third insect to be used quite extensively as a biocontrol agent is Urophora solstitialis (Julien and Griffiths, 1998). It has been used in Australia and New Zealand to destroy seeds produced late in the season which are not controlled by R. conicus. However, there have been some problems with competition between the two agents (Woodburn and Briese, 1996). There have been limited releases of Cheilosia corydon (=C. grossa), Psylliodes chalcomera and Puccinia carduorum in USA, but the impact of these species cannot yet be ascertained (Gassmann and Kok, 2002).
Research has been underway for a number of years in New Zealand to develop a mycoherbicide for C. nutans and several other thistle species using the fungus Sclerotinia sclerotiorum (Lib.) de Bary (Bourdot and Harvey, 1996), but a commercial product has still not been released from this work. Although there has been limited success to date in controlling C. nutans with biological control agents, it is generally agreed that they are an important component in any integrated weed control programme for this weed rather than as a sole control method (Woodburn and Briese, 1996).
As discussed by several authors, the most effective strategy for controlling C. nutans is to use a combination of regulatory, cultural, physical, biological and chemical techniques (e.g. Harrington, 1996; Huwer et al., 2002).
ReferencesTop of page
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Distribution MapsTop of page
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