Carduus pycnocephalus - L.
Italian Thistle
Other English Common Names: Italian Plumeless-thistle
Other Common Names: Italian plumeless thistle
Taxonomic Status: Accepted
Related ITIS Name(s): Carduus pycnocephalus L. (TSN 35788)
Unique Identifier: ELEMENT_GLOBAL.2.155762
Element Code: PDAST1S050
Informal Taxonomy: Plants, Vascular - Flowering Plants - Aster Family
 
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Dicotyledoneae Asterales Asteraceae Carduus
Check this box to expand all report sections:
Concept Reference
Help
Concept Reference: Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Concept Reference Code: B94KAR01HQUS
Name Used in Concept Reference: Carduus pycnocephalus
Conservation Status
Help

NatureServe Status

Global Status: GNR
Global Status Last Reviewed: 22Mar1994
Global Status Last Changed: 22Mar1994
Rounded Global Status: GNR - Not Yet Ranked
Nation: United States
National Status: NNA

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alabama (SNA), California (SNA), Hawaii (SNA), Idaho (SNA), New York (SNA), Oregon (SNA), Texas (SNA)

Other Statuses

NatureServe Global Conservation Status Factors

Range Extent Comments: Carduus pycnocephalus originated in western and southern Europe but today is widespread throughout temperate parts of the world. It is a serious pest in Australia, New Zealand, South Africa, Pakistan, Iran, and Europe. In the U.S. it is found in only a few parts of Texas and Arkansas but is rapidly spreading and "out of control" in most of California (Dunn 1976). C. pycnocephalus apparently arrived in California during the 1930s (Goeden 1974).

Other NatureServe Conservation Status Information

Distribution
Help
Global Range: Carduus pycnocephalus originated in western and southern Europe but today is widespread throughout temperate parts of the world. It is a serious pest in Australia, New Zealand, South Africa, Pakistan, Iran, and Europe. In the U.S. it is found in only a few parts of Texas and Arkansas but is rapidly spreading and "out of control" in most of California (Dunn 1976). C. pycnocephalus apparently arrived in California during the 1930s (Goeden 1974).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
NOTE: The distribution shown may be incomplete, particularly for some rapidly spreading exotic species.

U.S. & Canada State/Province Distribution
United States ALexotic, CAexotic, HIexotic, IDexotic, NYexotic, ORexotic, TXexotic

Range Map
No map available.

Ecology & Life History
Help
Basic Description: Carduus pycnocephalus, a member of the Thistle tribe of the Composite family, is an erect winter annual herb 3-18 dm tall.
Technical Description: The following description of Carduus pycnocephalus is adapted from Munz and Keck (1973), Parsons (1973), and Goeden (1974).

The name Carduus comes from the old Latin name for thistles. The stems are slender and narrowly spiny-winged, especially below. The lancolate leaves are pinnatifid, to about 12 cm. long, with spiny- tipped lobes and teeth, white-woolly below, greenish but more or less arachnoid above.

Branches end with a cluster of one to five rose-purple subcylindric flowerheads; the disk 1.5 cm wide. The phyllaries are not membranous-margined but are more or less persistantly floccose- tomentose. The corolla lobes are about threee times as long as the throat. The akenes are light tan or buff, about 20-nerved, and 5-6 mm long. The pappus is dull and 15-20 mm long. It reproduces only by its windborne or otherwise easily disseminated pappus achenes. Heterocarpy is well developed in Carduus pyncnocephalus (Bendall 1974). Hybridization between Carduus pycnocephalus and Carduus teniflorus has been reported in Europe (Batra et. al. 1981).

Diagnostic Characteristics: Carduus pycnocephalus can be distinguished from other thistle species by its relatively small and few terminal flowerheads and narrow phyllaries with copious tiny, firm, forward-pointing hairs, especially on the midrib (Hitchcock and Cronquist 1973).
Reproduction Comments: Carduus pycnocephalus reproduces only by seed. It prefers soils of high fertility, and its seedlings establish best on bare or disturbed sites (Wheatley 1971, Parsons 1973).

C. pycnocephalus seeds are mucilaginous, unlike most other thistles. The mucilage is abundant and adhesive enough to aid in seed dispersal (Evans et al. 1979).

C. pycnocephalus seeds exhibit polymorphism, with brown seeds that have less mucilage and germinate at lower temperatures than silver seeds. The brown seeds do not usually dehisce from the seedheads, and this may be important in the establishment of these seeds in the seedbed litter (Evans et al. 1979). GERMINATION AND GROWTH

Seed germination rate in Carduus pycnocephalus is very high, ranging between 83-96%. The seeds germinate at a wide variety of constant and alternating temperatures. The greatest diurnal fluctuation that supported optimum germination was 10 C for 16 hours and 35 C for 8 hours in each 24-hour period. Even with freezing temperatures during the daily cold period, germination was optimum if warm-period temperatures were from 5 to 20 C (Evans et al. 1979).

No after-ripening is required, and seeds can germinate either rapidly or after a long dormancy period. Seeds of C. pycnocephalus exhibit rapid germination (within 2 weeks) at optimum temperatures (Evans et al. 1979). Bendall (1974) found that 85% of Carduus pycnocephalus seeds produce germination inhibitors, but they are readily leached. The length of time the seeds can survive in the soil is not known but appears to be at least 8 years (Parsons 1973).

C. pycnocephalus can germinate at a variety of soil depths. Generally it does poorly on the surface of a bare seedbed, but on the surface of clay soils it shows 70% germination. At a depth of 0.5-2.0 cm germination is highest, but some seeds germinate to a depth of 8 cm (Evans et al. 1979). Seeds buried 1.3 cm deep show the highest percentage emergence, whereas 20 to 25% of seeds buried 5 to 10 cm deep remain dormant.

The growth of C. pycnocephalus is favored more by the addition of nitrogen than by phosphorus or potassium. High pH (6.5) also favors growth (Bendall 1975). SEED DISPERSAL

C. pycnocephalus does not reproduce vegetatively, but its seeds are well equipped for dispersal by wind because of the large pappus and relatively small size. The distance that seeds can be spread by wind is not known, but it is at least several hundred meters. Seeds are also spread when infested pastures are cut and the hay fed to animals on clean areas. Seed dispersal by water and on animals and machinery is less important (Parsons 1973). Ants may also play a role in dispersing the seeds (Uphof 1942).

Habitat Comments: It displaces desirable forage or cover plants, but more commonly colonizes disturbed habitats where interspecific competition is less intense (Goeden 1974). It is most abundant in coastal areas and occurs as a weed of pastures, ranges, roadsides, rural areas, fallow cropland, railroad rights-of-way, field margins, and ditchbanks (Goeden and Ricker 1978).

However, this weed does displace more desirable forage or cover plants. The blanketing effect of overwintering rosettes can severely reduce the establishment of other plants, as the leaves of the rosette can become erect in dense stands (Parsons 1973). If there is reasonable ground cover during the late summer and autumn the thistle will not invade a site, but it will come in following overgrazing or creation of fire breaks (Parsons 1973). Drought favors a rapid increase in the thistle population. On soils of naturally high fertility, thistle invasion can be expected at an earlier stage than on poorer soils. Thistles will invade basalt soils earlier than granite soils, and granite soils before sedimentary soils (Wheatley and Collett 1981).(Goeden and Ricker 1978).

C. pycnocephalus has been rapidly spreading on rangelands previ- ously dominated by alien annual grasses (Evans et al. 1979). This is partly due to its germination requirements and timing. C. pycnocephalus germinates at temperature and moisture regimes and in seedbed environments which would inhibit the germination of the alien annual grass species that presently dominate California grasslands. The seeds start to germinate in the fall with the first effective rain. Seedlings grow through the winter as rosettes and produce flowering stalks in the late spring before the summer drought.

Economic Attributes
Help
Economically Important Genus: Y
Management Summary
Help
Stewardship Overview: Carduus pycnocephalus, a vigorous annual thistle, arrived in California during the 1930s and has since become a serious weed problem. It occurs in a variety of disturbed habitats and germinates rapidly and in large numbers. Hand pulling, cultivation, and grazing are all effective control measures. Biological control agents, particularly the weevil Rhinocyllus conicus and the rust Puccinia Carduii-pycnocephali, show considerable promise in controlling C. pycnocephalus. Chemicals such as Picloram and 2,4-D may be of some use in controlling the weed, but an integrated management program involving a combination of techniques will prove most effective.
Species Impacts: Though some Carduus species are known to accumulate nitrates in toxic quantities, C. pycnocephalus has apparently not been incriminated as a toxic weed (Goeden 1974). The primary threat of this weed is its ability to dominate sites throughout California. C. pycnocephalus is a problem on Nature Conservancy property in this state and presents additional problems on grazed pastures. It reduces the establishment of annual grasses and reduces the value of hay and other crops due to the blanketing effect of the overwintering rosettes, high rate and timing of germination, and its broad range of germination conditions.
Management Requirements: With the right combination of control measures, it should be possible to eliminate C. pycnocephalus from selected areas. Its inability to reproduce vegetatively makes control easier, but constant monitoring will be necessary due to its potentially long seed dormancy (to 8 years).

Control of C. pycnocephalus requires active management once it becomes established in an area. Without management it cannot be eliminated and may completely carpet the site. MECHANICAL CONTROL

Cultivation before seed production will eventually eliminate thistles, but only if repeated for several years. According to Wheatley and Collett (1981), hand-hoeing is effective for small patches, but make sure to sever the root a good 10 cm below ground level. Mowing or slashing is not always reliable because the plant can regrow from the base and produce seeds very quickly.



Similarly, plants which are cut close to flowering time can produce seed on the cut portion. A significant amount of seed can be produced even if thistles are constantly mowed at 8 cm (Tasmanian Department of Agriculture 1977). Slashing is more effective than mowing as it destroys the aerial part of the plant more thoroughly (Parsons 1973).

For larger areas where the thistles are dominant, cultivation and cropping is a successful method of control provided a vigorous perennial pasture is established immediately after the cropping phase. In high fertility situations, using a roller to compact the soil is recommended during seedbed preparation (but not during seed sowing). This usually forces a massive germination of thistles that can be destroyed during cultivation (Wheatley and Collett 1981). GRAZING

Grazing by sheep, goats, and horses can be effective in control- ling thistles, but cattle are of little value (Parsons 1973). Bendall (1974) describes a grazing control method that has proven successful in Australia: thistle-infested areas are closed to grazing in the fall when seedlings appear. They are left ungrazed until the pasture has reached a height of 10-15 cm (about 6 to 10 weeks). The areas are then heavily grazed with sheep at more than twice the normal stocking rate. Sheep selectively graze the tender thistles and will kill 90-95% of the weeds. Only 2-3 weeks should be required for control. For this method to be successful, the autumn grazing break is necessary so that vigorous growth of other plants is allowed to occur, forcing the thistles to grow tall and tender. Continuous grazing significantly reduces thistle numbers but is not as effective as the use of an autumn break (Bendall 1973). BIOLOGICAL CONTROL

Biological control techniques for Carduus species have been extensively studied. Carduus pycnocephalus was one of the first weeds selected for biological control study by the USDA (Schroeder 1980). The search for its natural enemies has included Italy, Greece, Iran, and Pakistan, as well as southern California (Baloch et al. 1971, Baloch and Kahn 1973, Goeden 1974). According to Goeden (1974), C. pycnocephalus serves as an alternative food-plant or breeding host to a diversity of phytophagous insects, most of which are euryphagous, ectophagous, sap- or foliage-feeding species.

In southern Europe, more than 80 species are associated with C. pycnocephalus; about one third of them are stenophagous and restricted to host plants belonging to the tribe Cynareae.

In southern Europe, all major parts of C. pycnocephalus plants are damaged by one or more insect species, whereas in southern California the thistles are relatively free of insect damage. In California, more than 40 species of indigenous or introduced phytophagous insects have adopted this alien weed as an alternate food-plant, at least 15 of which also find it a suitable reproduc- tive host. Unfortunately, half of the identified species of insects found feeding on C. pycnocephalus in southern California are also pests of cultivated plants, thus not good choices for biocontrol.

Only three insect species appear to hold promise as biological control agents in California (Goeden 1974). These species are Psylliodes chalsomera, Rhinocyllus conicus, and Ceutorhynchuys trimaculatus. All three species are unknown as artichoke or safflower pests, apparently only reproduce on Cadruinae, cause injury to vital plant parts at a critical growth stage of their host-plant (and thus appear capable of influencing the reproductive potential of C. pycnocephalus), and occur over a relatively wide geographic area. However, according to Charles Turner (1985) of the USDA Biocontrol Lab in Albany, California, it is possible that these insects may also prey on several of the endangered native thistles in the genus CIRSIUM. Because of this concern, their use has been somewhat limited.

Psylliodes chalcomera was a fairly consistent associate of C. pycnocephalus in its vegetative and early reproductive stages throughout central and southern Italy. The adults are foliage feeders, but more importantly the larvae mine crowns of rosettes and tips of expanding and expanded shoots, blasting the latter, and thus reduce the production of flowerheads. This species has been studied in depth by USDA entomologists as a natural enemy of musk thistle, but certainly should also be considered for importation into California for C. pycnocephalus control" (Goeden 1974).

Larvae of Rhinocyllus conicus feed within the flowerheads of C. pycnocephalus, mining the receptacle and destroying the developing achenes (Goeden 1974, 1978). This weevil mainly reproduces on certain thistles belonging to the Carduus-Silybumcirsium complex. It survives best at low temperatures with short photoperiods (Kok 1979). Rhinocyllus conicus was first introduced into Canada in 1968 for the biological control of musk thistle (Carduus nutans L.) and plumeless thistle (Carduus acanthoides L.) (Harris and Zwolfer 1971).

It was imported into California in 1969 for the biological control of milk thistle (Silybum marianum Gaertn.) (Hawkes et al. 1972) and in 1973 to control C. pycnocephalus in southern California (Goeden and Ricker 1978). After their introduction to See Canyon in southern California, the weevil destroyed 90% of the achenes and infested 91% of the capitula; however, the population of C. pycnocephalus did not decline (Goeden and Ricker 1978). The weevil was released on infestations of Italian and slender-flower thistles at 16 sites in 11 counties in northern California during 1975-77 with establishment at most of the sites (Hawkes et al. 1978).

Certorhynchus trimaculatus occurs in Europe and northern Africa (Bolt et al. 1980). "Larvae thought to be Ceutorhynchus trimacu- latus were recovered from mines in crowns of C. pycnocephalus rosettes in central Italy, though only adults were positively identified as fairly consistent associates of this plant. This weevil has been studied in depth as a candidate biological control agent by USDA entomologists and may be usefully employed against C. pycnocephalus and other CARDUUS species in North America in the near future" (Goeden 1974).

The fungal rust Puccinia Carduii-pycnocephali Sydow, is known to occur only on the genus Carduus (Batra et al. 1981). Repeated greenhouse inoculations of the rust on growing rosettes signif- icantly reduced the growth of C. pycnocephalus but not the number of florets (Oliveri 1984). In field situations, the added hardship of intra- and interspecific competition may cause a greater effect on thistle populations. Optimum conditions for rust infection (18 to 20 C, 90 to 100% relative humidity) are likely to occur in autumn, in regions with a Mediterranean climate. This period also corresponds to the germination and vegetative growth periods of C. pycnocephalus (Oliveri 1984). Two other rusts, Puccinia centaureae dc and Puccinia galatica Sydow are also reported to attack Carduus pycnocephalus, but their impact has not been researched (Batra et al. 1981). CHEMICAL CONTROL

The use of herbicides to control C. pycnocephalus may not be appropriate on natural areas such as Nature Conservancy preserves. Near streams or lakes particular cautions should be taken when using herbicides. Prior to using any herbicide, check with the County Agricultural Commissioner to determine which chemicals are legal to use in a given situation. The labels also give more precise information on mixing and safety precautions. A Certified Pest Control Applicator should be hired for large jobs or those requiring nonselective herbicides.

A variety of herbicides have been used on C. pycnocephalus, but they give only temporary control (Wheatley and Collett 1981).

Picloram (Tordon): Dr. Jim McHenry (1985) of the University of California, Davis, recommends picloram to control C. pycnocephalus on Nature Conservancy lands. Since it is a nonselective herbicide, it must be carefully applied. It is most effective when applied in February or March at 1/8 to 1/16 lb acid equivalent per acre. Picloram kills half the test animals (LD50) at 8000 mg/kg body weight and is considered to be of "relatively no hazard." One drawback is its long persistence in the soil, up to 18 months.

2,4-D: 2,4-D is a phenoxy-type herbicide used for broadleaf weed control that works as a selective hormone or growth regulator. 2,4-D does not affect grasses. It is foliar absorbed and trans- located, making it effective in destroying the roots. 2,4-D is available in ester, amine, emulsifiable acid, and low volatile ester formulations. The chemical is noncorrosive and is generally considered nonharmful to wildlife. 2,4-D is lethal to 50% of tested animals (LD50) at 300-1000 mg/kg body weight and is classified as being of "little" to "some" hazard. It persists in the soil for 1-4 weeks.

2,4-D has been applied to C. pycnocephalus with limited success (Taylor 1977). 2,4-D ester should be applied when the thistles have a central stock height of no greater than 0.25 m (Wheatley and Collett 1981). Application should be at the rate of 1-1.5 lbs/100 gallons of water with 1 quart of surfactant/100 gallons. Surfactants affect the surface property of the spray by lowering surface tension to increase the herbicide's effectiveness.

2,4-D can be used in combination with biological control measures to control Carduus. Several recent studies (Kok 1980, Trumble and Kok 1980a, 1980b) have shown that the weevil Rhinocyllus conicus is not adversely affected by field applications of 2,4-D.

Selective weed oils: There are several petroleum oils used for weed control. The herbicidal use of oils depends on their chemical and physical properties. Most contact oils evaporate slowly and owe their plant toxicity to their high content of aromatic compounds. Spraying oil on thistle will be effective only if entire plants are coated.

APPLYING HERBICIDES: Herbicides can be applied uniformly over an area (for large infestations) or by spot spraying only the individual plants. Dr. McHenry recommends using a flat-fan nozzle (Spraying Systems Co. #8003 or 8004 nozzle tip) rather than the cone nozzles available on most garden sprayers. Cone sprayers produce greater atomization of the chemicals and increase the chance of drift into unwanted areas. Spraying should be done on calm days with dry plants (dew or rain will dilute the herbicide, reducing its effectiveness). When spraying large areas, a horizontal boom (6-8 feet long) made from aluminum tubing will improve herbicide coverage.

Monitoring Requirements: Monitoring is needed to determine the effectiveness of any C. pycnocephalus control measures. The necessity for constant monitoring is all the more important given this weed's potentially long seed dormancy period (to 8 years).

Management Programs: Carduus pycnocephalus is present on both the Ring Mountain and Jepson Prairie preserves in California, with Ring Mountain having the most significant infestation. Although other thistle species present greater problems on these preserves, C. pycnocephalus control has been included as an adjunct to other control efforts. Former preserve manager Greg Wolley (1986) has used both hand pulling and cutting to destroy the plants at Ring Mountain Preserve, CA. This has proven most effective during the spring and early summer.

Contact: Larry Serpa, Area Manager. 3152 Paradise Drive, Room 101, Tiburon, CA 94920. Tel.(415) 435-6465.

Management Research Needs: A great deal of research has been conducted on Carduus species throughout the world, but much more needs to be done on Carduus pycnocephalus. Additional research needs to be conducted on insects that can be used to control C. pycnocephalus and on the potential impact of these insects upon endangered native Cirsium species (Kok et al. 1982). Several management techniques appear promising, and integrated control operations involving a combina- tion of practices need investigation. The effects of prescribed fire on C. pycnocephalus also need investigation.
Population/Occurrence Delineation Not yet assessed
Help
Population/Occurrence Viability
Help
U.S. Invasive Species Impact Rank (I-Rank)
Help
Disclaimer: While I-Rank information is available over NatureServe Explorer, NatureServe is not actively developing or maintaining these data. Species with I-RANKs do not represent a random sample of species exotic in the United States; available assessments may be biased toward those species with higher-than-average impact.

I-Rank: Medium
Rounded I-Rank: Medium
I-Rank Reasons Summary: This winter annual is mostly a problem in California in a variety of disturbed habitats. It germinates rapidly and in large numbers. Control can be achieved through a variety of methods, including hand pulling, cultivation, and grazing, as well as biological control agents.
Subrank I - Ecological Impact: Low
Subrank II - Current Distribution/Abundance: High
Subrank III - Trend in Distribution/Abundance: Medium
Subrank IV - Management Difficulty: Medium/Low
I-Rank Review Date: 25Jan2004
Evaluator: Lu, S.
Native anywhere in the U.S?
Native Range: Native to Central, Southern, and Eastern Europe, as well as northern Africa, Mediterranean islands, Asia, Canary Islands, Madeira Islands, and the Azores (Weber 2003). Native to the Mediterranean, southern Europe, and North Africa to Pakistan (Bossard et al. 2000).

Download "An Invasive Species Assessment Protocol: Evaluating Non-Native Plants for their Impact on Biodiversity". (PDF, 1.03MB)
Provide feedback on the information presented in this assessment

Screening Questions

S-1. Established outside cultivation as a non-native? YES
Comments: This species is a non-native that is established outside of cultivation (Kartesz 1999).

S-2. Present in conservation areas or other native species habitat? Yes
Comments: Invasive in the United States (BLM CO 2004), specifically in California (Pitcher and Russo 1988; Beedy and Brussard 2002).

Subrank I - Ecological Impact: Low

1. Impact on Ecosystem Processes and System-wide Parameters:Low significance
Comments: In savannas, it can carry grass fires to tree canopies and thus increases fire hazards (Weber 2003). About 85% of seeds produce germination inhibitors, but they leach readily (Pitcher and Russo 1988).

2. Impact on Ecological Community Structure:Low significance
Comments: Carduus pycnocephalus can become dominant and exclude native species. The cover of overwintering rosettes prevents the establishment of other plant species. (Weber 2003; Pitcher and Russo 1988) Reduces the establishment of annual grasses (Pitcher and Russo 1988). This plant has been rapidly spreading on rangelands previously dominated by alien annual grasses. (Pitcher and Russo 1988)

3. Impact on Ecological Community Composition:Moderate significance
Comments: Carduus pycnocephalus can become dominant and exclude native species. The cover of overwintering rosettes prevents the establishment of other plant species. (Weber 2003; Pitcher and Russo 1988) Reduces the establishment of annual grasses (Pitcher and Russo 1988).

4. Impact on Individual Native Plant or Animal Species:Insignificant
Comments: No reported impacts.

5. Conservation Significance of the Communities and Native Species Threatened:Low significance
Comments: Found primarily in disturbed habitats and inhabits common, unthreatened habitats (Weber 2003; Pitcher and Russo 1988; Beedy and Brussard 2002).

Subrank II. Current Distribution and Abundance: High

6. Current Range Size in Nation:High significance
Comments: Established in 9 mainly coastal states, Alabama, Arkansas, California, Hawaii, Idaho, New York, Oregon, South Carolina, Texas (Kartesz 1999). In the US it is found in only a few parts of Texas and Arkansas but is rapidly spreading and out of control in most of California (Pitcher and Russo 1988).

7. Proportion of Current Range Where the Species is Negatively Impacting Biodiversity:Moderate significance
Comments: Able to dominate site throughout California except for the Great Basin and northern Mojave Desert (Bossard et al. 2000) (~20% of land area of states occupied) and is rapidly spreading and out of control in there (Pitcher and Russo 1988; Beedy and Brussard 2002). In Hawaii, but is not invasive in natural areas. Also not a problem in non-western areas in the US. (Weber 2003)

8. Proportion of Nation's Biogeographic Units Invaded:High/Low significance
Comments: At least in 4 TNC ecoregion, and at most in 45 ecoregions (Inference using data from Kartesz 1999 and TNC Ecoregion 2001 map).

9. Diversity of Habitats or Ecological Systems Invaded in Nation:High significance
Comments: It is most abundant in coastal areas and occurs as a weed of pastures, ranges, roadsides, rural areas, fallow cropland, railroad rights-of-way, field margins, and ditchbanks. It establishes best on bare or disturbed sites but willl not invade a site with reasonable ground cover during the late summer or autumn. However, it will come in following overgrazing or creation of fire breaks. Drought will likely cause a rapid increase in the thistle population. This plant has been rapidly spreading on rangelands previously dominated by alien annual grasses. (Pitcher and Russo 1988)Invades grasslands, scrub, woodland, and disturbed places (Weber 2003). In the inner Coast Ranges from Solano County north in California, this plant is common in chaparral and oak savanna (Bossard et al. 2000). In Nevada County California, it is found in grasslands, shrub lands, and oak woodlands (Beedy and Brussard 2002). In Hawaii, it recently naturalized in dry sites on the western slopes of Haleakala on Maui (Wagner et al. 1990)

Subrank III. Trend in Distribution and Abundance: Medium

10. Current Trend in Total Range within Nation:Low significance
Comments: Arrived in California during the 1930s and is still rapidly spreading throughout California (Pitcher and Russo 1988), but no reports of spread outside of California.

11. Proportion of Potential Range Currently Occupied:Unknown

12. Long-distance Dispersal Potential within Nation:Medium/Low significance
Comments: The seeds are very small in size, 4-5 mm (Rees et al. 1996) and have a large pappus, which allow for wind dispersal. (Pitcher and Russo 1988). Seeds can disperse 75 feet by wind and 325 feet in strong winds (Bossard et al. 2000).; The seeds are also very mucilaginous. They are adhesive enough to aid in seed dispersal. Other dispersal mechanisms include seed contaminated hay, soil from infested quarries, water, animals, and ants. (Pitcher and Russo 1988; Bossard et al. 2000)

13. Local Range Expansion or Change in Abundance:High significance
Comments: Arrived in California during the 1930s and is still rapidly spreading throughout California (Pitcher and Russo 1988).

14. Inherent Ability to Invade Conservation Areas and Other Native Species Habitats:Low significance
Comments: Invades disturbed places (Weber 2003). Likes to colonize disturbed habitats or bare sites where interspecific competition is less intense (Pitcher and Russo 1988).

15. Similar Habitats Invaded Elsewhere:High/Low significance
Comments: This plant is widespread throughout temperate parts of the world. It is a serious pest in Australia, New Zealand, South Africa, Pakistan, Iran, and Europe. (Pitcher and Russo 1988). Invades in Australia also. However it is present in but does not invade natural areas in New Zealand, South America, northern Europe, or southern Africa (Weber 2003).

16. Reproductive Characteristics:High significance
Comments: This plant is very reproductively aggressive. Fruit production is prolific - up to 20,000 seeds per year per plant, and seeds are viable up to 10 years (Weber 2003). It only reproduces by seed but the seeds exhibit polymorphism and have a very high germination rate, 83-96%. They also exhibit rapid germination of within 2 weeks and has a broad range of germination conditions. About 85% of seeds produce germination inhibitors, but they leach readily. Drought will likely cause a rapid increase in the thistle population (Pitcher and Russo 1988).

Subrank IV. General Management Difficulty: Medium/Low

17. General Management Difficulty:Moderate significance
Comments: An integrated long-term plan with persistent follow-up and twice-yearly monitoring is needed to eliminate this thistle (Bossard et al. 2000). Control requires active management but is easier because of its inability to reproduce vegetatively (Pitcher 1986). Control can be achieved by hand pulling, mowing, grazing (sheep, goats, and horses, NOT cattle), herbicides, or biocontrol using the weevil Phinocyllus conicus and the rust Puccinia Carduii-pycnocephali (Weber 2003; Pitcher and Russo 1988).

18. Minimum Time Commitment:Moderate significance
Comments: Up to 8 or 10 years of constant monitoring is necessary due to its potentially long seed dormancy (Pitcher and Russo 1988; Bossard et al. 2000).

19. Impacts of Management on Native Species:Medium significance/Insignificant
Comments: Biological control may possible impact native endangered Cirsium species (Pitcher and Russo 1988).

20. Accessibility of Invaded Areas:Unknown
Authors/Contributors
Help
NatureServe Conservation Status Factors Edition Date: 18Oct1988
NatureServe Conservation Status Factors Author: DON PITCHER [86-12-04], MARY J. RUSSO (Revision)
Management Information Edition Date: 18Oct1988
Management Information Edition Author: DON PITCHER [86-12-04], MARY J. RUSSO (Revision)

Botanical data developed by NatureServe and its network of natural heritage programs (see Local Programs), The North Carolina Botanical Garden, and other contributors and cooperators (see Sources).

References
Help
  • BLM Colorado. 2004. BLM national list of invasive weed species of concern. Available: http://www.co.blm.gov/botany/invasiweed.htm. (Accessed 2004).

  • Baloch, G.M., A.G. Khan, and M. Mushtaque. 1971. Biological control of CARDUUS spp. (Compositae: I. Insects associated with these in West Pakistan). Commonwealth Institute of Biological Control, Technical Bulletin 14:51-58.

  • Baloch, G.M., and A.G. Khan. 1973. Biological control of CARDUUS species. II. Phenology, biology and host-specificity of TERELLIA SERRATULAE L. (Diptera: Trypetidae). Commonwealth Institute of Biological Control, Technical Bulletin 16:11-22.

  • Batra, S.W.T., J.R. Coulson, P.H. Dunn, and P.E. Boldt. 1981. Insects and fungi associated with CARDUUS thistles (Compositae). USDA Technical Bulletin No. 1616. 100 pp.

  • Beedy, E.C. and P. Brussard. 2002. Nevada County natural resources report: a scientific assessment of watersheds and ecosystems. Table 3-2 - Noxious weeds and other invasive non-native plants known to occur in Nevada County. Nevada County Planning Department. Available: http://nevadacountynature.org/images/table3-2.pdf. (Accessed 2004).

  • Bendall, G.M. 197. The control of slender thistle, CARDUUS PYCNOCEPHALUS L. and CARDUUS TENUIFLORUS Curt. (Compositae), in pasture by grazing management. Australian Journal of Agricultural Research 24:831-837.

  • Bendall, G.M. 1974. Slender thistles in pasture: control by grazing management. Tasmanian Journal of Agricultural Research 45:62-63.

  • Bendall, G.M. 1975. Some aspects of the biology, ecology, and control of slender thistle, CARDUUS PYCNOCEPHALUS L. and C. TENUIFLORUS Curt. (Compositae), in Tasmania. Journal of Australian Institute of Agricultural Science 41:52-53.

  • Bolt, P.E., G. Campobasso, and E. Colonnelli. 1980. Palearctic distribution and host plants of CEUTORHYNCHS TRIMACULATUS and TRICHOSIROCALUS HORRIDUS (Coleoptera: Curculionidae). Annals of the Entomological Society of America 73:694-698.

  • Bossard, C.C., J.M. Randall, and M. Hoshovsky. (eds.) 2000. Invasive Plants of California's Wildlands. University of California Press, Berkeley, CA.

  • Dunn, P.H. 1976. Distribution of CARDUUS NUTANS, C. ACANTHOIDES, C. PUCNOCEPHALUS, and C. CRISPUS, in the United States. Weed Science 24:518-524.

  • Evans, R.A., J.A. Young, and R. Hawkes. 1979. Germination characteristics of Italian thistle (CARDUUS PYCNOCEPHALUS) and slenderflower thistle (CARDUUS TENUIFLORUS). Weed Science 27:327-332.

  • Goeden, R.D. 1974. Comparative survey of the phytophagous insect faunas of Italian thistle, CARDUUS PYCNOCEPHALUS in southern California and southern Europe relative to biological weed control. Environmental Entomology 3:464-474.

  • Goeden, R.D. 1978. Initial analyses of RHINOCYLLUS CONICUS (Froelich)(Col. Curculionidae) as an introduced natural enemy of milk thistle (SILYBUM MARIANUM (L.)Gaertner) and Italian thistle (CARDUUS PYCNOCEPHALUS L.) in southern California. Pages 39-50 in K.E. Frick. Biological control of thistles in the genus CARDUUS in the United States.

  • Goeden, R.D., and D.W. Ricker. 1978. Establishment of RHINOCYLLUS CONICUS (Col. Corculionidae) on Italian thistle in southern California. Environmental Entomology 7:787-789.

  • Harris, P., and H. Zwolfer. 1971. CARDUUS ACANTHOIDES L., welted thistle, and C. NUTANS L., nodding thistle (Compositae). Pages 76-79 in Biological control programmes against insects and weeds in Canada 1959-68. Tech. Commun. Commonw. Inst. Biological Control 4.

  • Hawkes, R.B., C.A. Andres, and P.H. Dunn. 1972. Seed weevil released to control milk thistle. California Agriculture, December, p.14.

  • Hawkes, R.B., L.A. Andres, P.H. Dunn, and D.M. Maddox. 1978. Biological control of problem weeds in non-cropland areas. Pages 71-75 in Proc. 30th Anniversary California Weed Conference.

  • Hitchcock, C.L., and A. Cronquist. 1973. Flora of the Pacific Northwest: An Illustrated Manual. University of Washington Press, Seattle, Washington. 730 pp.

  • Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.

  • Kartesz, J.T. 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. First edition. In: Kartesz, J.T., and C.A. Meacham. Synthesis of the North American Flora, Version 1.0. North Carolina Botanical Garden, Chapel Hill, N.C.

  • Kok, L.T. 1979. Influence of temperature and photoperiod on the mortality of diapausing RHINOCYLLUS CONICUS (Coleoptera: Curculionidae). Annals of the Entomological Society of America 72:206-208.

  • Kok, L.T. 1980. Compatibility of RHINOCYLLUS CONICUS, TRICHOSIROCALUS HORRIDUS and 2,4-D for CARDUUS thistle control. Proc. V Int. Symp. Biol. Contr. Weeds, Brisbane, Australia:441-445.

  • Kok, L.T., T.J. McAvoy, G.R. Johnson, and P.H. Dunn. 1982. Further tests on CEUTORHYNCHUS TRIMACULATUS R. as a candidate for the biological control of CARDUUS thistles. Crop Protection 1:67-74.

  • Munz, P.A., and D.D. Keck. 1973. A California Flora and Supplement. University of California Press, Berkeley, CA. 1905 pp.

  • Oliveri, I. 1984. Effect of PUCCINIA CARDUI-PYCNOCEPHALI on slender thistles (CARDUUS PYCNOCEPHALUS and C. TENUIFLORUS). Weed Science 32:508-510.

  • Oregon State University Extension Service. 1999. Problem thistles of Oregon. Available: http://eesc.orst.edu/agcomwebfile/edmat/EC1288.pdf. (Accessed 2004).

  • Parsons, W. T. 1973. Noxious weeds of Victoria. Inkata Press, Ltd., Melbourne, Australia. 300 pp.

  • Pitcher, D. and M.J. Russo. 1988. Element stewardship abstract for Carduus pycnocephalus. The Nature Conservancy: Arlington, VA. Available: http://tncweeds.ucdavis.edu/esadocs/cardpycn.html. (Accessed 2004).

  • Rees, N.E., P.C. Quimby Jr., G.L. Piper, E.M. Coombs, C.E. Turner, N.R. Spencer, and L.V. Knutson, editors. 1996. The biological control of weeds in the west. Western Society of Weed Science in Cooperation with the USDA Agricultural Research Service, Montana Department of Agriculture, and Montana State University. Color World Printer, Bozeman, Montana. Exceprts available: http://www.weedcenter.org/info/weedlist.html.

  • Schroeder, D. 1980. The biological control of thistles. Biocontrol News and Information 1:9-26.

  • Tasmanian Department of Agriculture. 1977. Annual report 1976-77. Tasmania, Government Printer. No. 64. 88 pp.

  • Taylor, R.L. 1977. Control of winged and slender winged thistles. Proc. 30th New Zealand Weed and Pest Control Conference: 38-41.

  • The Nature Conservancy. 2001. Map: TNC Ecoregions of the United States. Modification of Bailey Ecoregions. Online . Accessed May 2003.

  • Trumble, J.T., and L.T. Kok. 1980a. Impact of 2,4-D on CEUTHORHYNCHIDIUS HORRIDUS (Coleoptera: Curculionidae) and their compatibility for integrated control of CARDUUS thistles. Weed Research 20:73-75.

  • Trumble, J.T., and L.T. Kok. 1980b. Integration of thistle-head weevil and herbicide for CARDUUS thistle control. Protection Ecology 2:57-64.

  • Turner, Charles. 1985. USDA Biological Control Lab, Albany, California. Personal Communication.

  • Uphof, J. C. Th. 1942. Ecological relations of plants with ants and termites. The Botanical Review 8(9):563-598.

  • Wagner, W.L., D.R. Herbst, and S.H. Sohmer. 1990. Manual of the flowering plants of Hawaii. Univ. Hawaii Press and Bishop Museum Press, Honolulu. 1853 pp.

  • Weber, E. 2003. Invasive plant species of the world: a reference guide to environmental weeds. CABI Publishing, Cambridge, Massachusetts. 548 pp.

  • Wheatley, W. M. 1971. Thistles - Prickly problem of pasture improvement. The Agricultural Gazette of New South Wales 82(5): 258-261.

  • Wheatley, W.M., and I.J. Collett. 1981. Winning the thistle war. Agricultural Gazette of New South Wales 92:25-28.

Use Guidelines & Citation

Use Guidelines and Citation

The Small Print: Trademark, Copyright, Citation Guidelines, Restrictions on Use, and Information Disclaimer.

Note: All species and ecological community data presented in NatureServe Explorer at http://explorer.natureserve.org were updated to be current with NatureServe's central databases as of March 2019.
Note: This report was printed on

Trademark Notice: "NatureServe", NatureServe Explorer, The NatureServe logo, and all other names of NatureServe programs referenced herein are trademarks of NatureServe. Any other product or company names mentioned herein are the trademarks of their respective owners.

Copyright Notice: Copyright © 2019 NatureServe, 2511 Richmond (Jefferson Davis) Highway, Suite 930, Arlington, VA 22202, U.S.A. All Rights Reserved. Each document delivered from this server or web site may contain other proprietary notices and copyright information relating to that document. The following citation should be used in any published materials which reference the web site.

Citation for data on website including State Distribution, Watershed, and Reptile Range maps:
NatureServe. 2019. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. Available http://explorer.natureserve.org. (Accessed:

Citation for Bird Range Maps of North America:
Ridgely, R.S., T.F. Allnutt, T. Brooks, D.K. McNicol, D.W. Mehlman, B.E. Young, and J.R. Zook. 2003. Digital Distribution Maps of the Birds of the Western Hemisphere, version 1.0. NatureServe, Arlington, Virginia, USA.

Acknowledgement Statement for Bird Range Maps of North America:
"Data provided by NatureServe in collaboration with Robert Ridgely, James Zook, The Nature Conservancy - Migratory Bird Program, Conservation International - CABS, World Wildlife Fund - US, and Environment Canada - WILDSPACE."

Citation for Mammal Range Maps of North America:
Patterson, B.D., G. Ceballos, W. Sechrest, M.F. Tognelli, T. Brooks, L. Luna, P. Ortega, I. Salazar, and B.E. Young. 2003. Digital Distribution Maps of the Mammals of the Western Hemisphere, version 1.0. NatureServe, Arlington, Virginia, USA.

Acknowledgement Statement for Mammal Range Maps of North America:
"Data provided by NatureServe in collaboration with Bruce Patterson, Wes Sechrest, Marcelo Tognelli, Gerardo Ceballos, The Nature Conservancy-Migratory Bird Program, Conservation International-CABS, World Wildlife Fund-US, and Environment Canada-WILDSPACE."

Citation for Amphibian Range Maps of the Western Hemisphere:
IUCN, Conservation International, and NatureServe. 2004. Global Amphibian Assessment. IUCN, Conservation International, and NatureServe, Washington, DC and Arlington, Virginia, USA.

Acknowledgement Statement for Amphibian Range Maps of the Western Hemisphere:
"Data developed as part of the Global Amphibian Assessment and provided by IUCN-World Conservation Union, Conservation International and NatureServe."

NOTE: Full metadata for the Bird Range Maps of North America is available at:
http://www.natureserve.org/library/birdDistributionmapsmetadatav1.pdf.

Full metadata for the Mammal Range Maps of North America is available at:
http://www.natureserve.org/library/mammalsDistributionmetadatav1.pdf.

Restrictions on Use: Permission to use, copy and distribute documents delivered from this server is hereby granted under the following conditions:
  1. The above copyright notice must appear in all copies;
  2. Any use of the documents available from this server must be for informational purposes only and in no instance for commercial purposes;
  3. Some data may be downloaded to files and altered in format for analytical purposes, however the data should still be referenced using the citation above;
  4. No graphics available from this server can be used, copied or distributed separate from the accompanying text. Any rights not expressly granted herein are reserved by NatureServe. Nothing contained herein shall be construed as conferring by implication, estoppel, or otherwise any license or right under any trademark of NatureServe. No trademark owned by NatureServe may be used in advertising or promotion pertaining to the distribution of documents delivered from this server without specific advance permission from NatureServe. Except as expressly provided above, nothing contained herein shall be construed as conferring any license or right under any NatureServe copyright.
Information Warranty Disclaimer: All documents and related graphics provided by this server and any other documents which are referenced by or linked to this server are provided "as is" without warranty as to the currentness, completeness, or accuracy of any specific data. NatureServe hereby disclaims all warranties and conditions with regard to any documents provided by this server or any other documents which are referenced by or linked to this server, including but not limited to all implied warranties and conditions of merchantibility, fitness for a particular purpose, and non-infringement. NatureServe makes no representations about the suitability of the information delivered from this server or any other documents that are referenced to or linked to this server. In no event shall NatureServe be liable for any special, indirect, incidental, consequential damages, or for damages of any kind arising out of or in connection with the use or performance of information contained in any documents provided by this server or in any other documents which are referenced by or linked to this server, under any theory of liability used. NatureServe may update or make changes to the documents provided by this server at any time without notice; however, NatureServe makes no commitment to update the information contained herein. Since the data in the central databases are continually being updated, it is advisable to refresh data retrieved at least once a year after its receipt. The data provided is for planning, assessment, and informational purposes. Site specific projects or activities should be reviewed for potential environmental impacts with appropriate regulatory agencies. If ground-disturbing activities are proposed on a site, the appropriate state natural heritage program(s) or conservation data center can be contacted for a site-specific review of the project area (see Visit Local Programs).

Feedback Request: NatureServe encourages users to let us know of any errors or significant omissions that you find in the data through (see Contact Us). Your comments will be very valuable in improving the overall quality of our databases for the benefit of all users.