Pacific Island Ecosystems at Risk (PIER)


Silybum marianum


RISK ASSESSMENT RESULTS: High risk, score: 17.5


Australian/New Zealand Weed Risk Assessment adapted for Hawai‘i.
Information on Risk Assessments
Original risk assessment

Silybum marianum (L.) Gaertn. Family - Asteraceae. Common Names(s) - milk thistle, blessed milk-thistle, spotted thistle, variegated thistle . Synonym(s) - Carduus marianus L., Mariana mariana (L.) Hill.

Answer

Score

1.01

Is the species highly domesticated?

y=-3, n=0

n

0

1.02

Has the species become naturalized where grown?

y=1, n=-1

1.03

Does the species have weedy races?

y=-1, n=-1

2.01

Species suited to tropical or subtropical climate(s) (0-low; 1-intermediate; 2-high) – If island is primarily wet habitat, then substitute “wet tropical” for “tropical or subtropical”

See Append 2

1

2.02

Quality of climate match data (0-low; 1-intermediate; 2-high) see appendix 2

1

2.03

Broad climate suitability (environmental versatility)

y=1, n=0

y

1

2.04

Native or naturalized in regions with tropical or subtropical climates

y=1, n=0

y

1

2.05

Does the species have a history of repeated introductions outside its natural range?

y=-2, ?=-1, n=0

y

3.01

Naturalized beyond native range y = 1*multiplier (see Append 2), n= question 2.05

y

1.5

3.02

Garden/amenity/disturbance weed y = 1*multiplier (see Append 2)

n=0

y

3.03

Agricultural/forestry/horticultural weed y = 2*multiplier (see Append 2)

n=0

y

3

3.04

Environmental weed y = 2*multiplier (see Append 2)

n=0

y

3

3.05

Congeneric weed y = 1*multiplier (see Append 2)

n=0

n

0

4.01

Produces spines, thorns or burrs

y=1, n=0

y

1

4.02

Allelopathic

y=1, n=0

n

0

4.03

Parasitic

y=1, n=0

n

0

4.04

Unpalatable to grazing animals

y=1, n=-1

n

-1

4.05

Toxic to animals

y=1, n=0

n

0

4.06

Host for recognized pests and pathogens

y=1, n=0

n

0

4.07

Causes allergies or is otherwise toxic to humans

y=1, n=0

n

0

4.08

Creates a fire hazard in natural ecosystems

y=1, n=0

n

0

4.09

Is a shade tolerant plant at some stage of its life cycle

y=1, n=0

n

0

4.10

Tolerates a wide range of soil conditions (or limestone conditions if not a volcanic island)

y=1, n=0

y

1

4.11

Climbing or smothering growth habit

y=1, n=0

n

0

4.12

Forms dense thickets

y=1, n=0

y

1

5.01

Aquatic

y=5, n=0

n

0

5.02

Grass

y=1, n=0

n

0

5.03

Nitrogen fixing woody plant

y=1, n=0

n

0

5.04

Geophyte (herbaceous with underground storage organs -- bulbs, corms, or tubers)

y=1, n=0

n

0

6.01

Evidence of substantial reproductive failure in native habitat

y=1, n=0

n

0

6.02

Produces viable seed.

y=1, n=-1

y

1

6.03

Hybridizes naturally

y=1, n=-1

6.04

Self-compatible or apomictic

y=1, n=-1

6.05

Requires specialist pollinators

y=-1, n=0

n

0

6.06

Reproduction by vegetative fragmentation

y=1, n=-1

n

-1

6.07

Minimum generative time (years) 1 year = 1, 2 or 3 years = 0, 4+ years = -1

See left

1

1

7.01

Propagules likely to be dispersed unintentionally (plants growing in heavily trafficked areas)

y=1, n=-1

y

1

7.02

Propagules dispersed intentionally by people

y=1, n=-1

y

1

7.03

Propagules likely to disperse as a produce contaminant

y=1, n=-1

y

1

7.04

Propagules adapted to wind dispersal

y=1, n=-1

y

1

7.05

Propagules water dispersed

y=1, n=-1

y

1

7.06

Propagules bird dispersed

y=1, n=-1

n

-1

7.07

Propagules dispersed by other animals (externally)

y=1, n=-1

y

1

7.08

Propagules survive passage through the gut

y=1, n=-1

n

-1

8.01

Prolific seed production (>1000/m2)

y=1, n=-1

y

1

8.02

Evidence that a persistent propagule bank is formed (>1 yr)

y=1, n=-1

y

1

8.03

Well controlled by herbicides

y=-1, n=1

y

-1

8.04

Tolerates, or benefits from, mutilation, cultivation, or fire

y=1, n=-1

8.05

Effective natural enemies present locally (e.g. introduced biocontrol agents)

y=-1, n=1

Total score:

17.5

Supporting data:

Notes

Source

1.01

(1)Blessed milkthistle has been used medicinally for at least 2000 years [with no apparent loss in weediness[

(1)DiTomaso, J. M. and E. A. Healy. 2007. Weeds of California and Other Western States. ANR Publications. Oakland, CA.

1.02

1.03

2.01

(1)Variegated thistle originated in the Mediterranean region, Asia Minor and the Soviet Union. It has now spread to most temperate areas of the world and is considered an important weed in many of them. (2)Variegated thistle (Silybum marianum) is widely distributed in Mediterranean Europe and north Africa, where it occurs primarily on disturbed and nutrient-enriched land. The species has been introduced to other regions with a Mediterranean climate, such as California, Chile and southern Australia where it is a weed of grazing lands.

(1)Parsons, W.T. and E. G. Cuthbertson. 2001. Noxious weeds of Australia. CSIRO Publishing. Collingwood, Australia. (2)Groves, R. H. and J.J. Burdon. 1996. The use of pathogens native to Europe to control thistles in southern Australia. Plant Protection Quarterly 11(Supplement 2): 256-258.

2.02

2.03

(1)Hardiness:
USDA Zone 5a: to -28.8 °C (-20 °F)
USDA Zone 5b: to -26.1 °C (-15 °F)
USDA Zone 6a: to -23.3 °C (-10 °F)
USDA Zone 6b: to -20.5 °C (-5 °F)
USDA Zone 7a: to -17.7 °C (0 °F)
USDA Zone 7b: to -14.9 °C (5 °F)
USDA Zone 8a: to -12.2 °C (10 °F)
USDA Zone 8b: to -9.4 °C (15 °F)
USDA Zone 9a: to -6.6 °C (20 °F)
USDA Zone 9b: to -3.8 °C (25 °F)

(1)http://davesgarden.com/guides/pf/go/1056/ [Accessed 25 Mar 2009]

2.04

(1)Small daily and yearly temperature deviations as well as no frost are characteristics of a marginal tropical climate [naturalized in Canary Islands, subtropical]

(1)Brandes, D. and K. Fritzsch. 2002. Alien plants of Fuerteventura, Canary Islands. http://www.maltawildplants.com/ASTR/Docs/ASTSQ/Canary_Aliens.pdf [Accessed 25 Mar 2009]

2.05

(1)Variegated thistle originated in the Mediterranean region, Asia Minor and the Soviet Union. It has now spread to most temperate areas of the world and is considered an important weed in many of them. Variegated thistle is common in the western United States in pastures and neglected areas, and on channel banks. It is a common weed in sheep areas of New Zealand and is regarded as weedy in South Arica, South America (Argentina and Brazil) and Afghanistan, and within its native range throughout Europe and Tunisia, Israel, Jordan and Iraq.

(1)Parsons, W.T. and E. G. Cuthbertson. 2001. Noxious weeds of Australia. CSIRO Publishing. Collingwood, Australia.

3.01

(1)Variegated thistle originated in the Mediterranean region, Asia Minor and the Soviet Union. It has now spread to most temperate areas of the world and is considered an important weed in many of them. Variegated thistle is common in the western United States in pastures and neglected areas, and on channel banks. It is a common weed in sheep areas of New Zealand and is regarded as weedy in South Africa, South America (Argentina and Brazil) and Afghanistan, and within its native range throughout Europe and Tunisia, Israel, Jordan and Iraq.

(1)Parsons, W.T. and E. G. Cuthbertson. 2001. Noxious weeds of Australia. CSIRO Publishing. Collingwood, Australia.

3.02

(1)In his observations of the species in southeast Australia, Parsons (1973) usually found it on soils of alluvial or volcanic origin, on the soils of river flats and in places where N was plentiful. In agriculture and forest lands it was found wherever soil was disturbed, on fire lanes of ranges and forests, on farm roads, around animal camps and yards and near rabbit warrens. Grasslands become susceptible to invasions by the species if dry weather in late summer and autumn results in breaks in the cover so that thistle seedlings become established. [a disturbance adapted weed of agriculture and natural settings, already scored for question 3.04]

(1)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York.

3.03

(1)In New Zealand, this species is a serious weed in open pastures and waste places, but particularly in coastal areas. Unconsolidated sands and light, stony soils that dry out badly in summer are likely to have good stands of S. marianum. Glue and Matthews (1957) found it to be the largest and fastest growing of all the common thistles in the country. (2)Blessed milkthistle is a state-listed noxious weed in Oregon (class B) and Washington (class A) and is a government-listed noxious weed in much of southern Australia. (3)The Mediterranean climate of California has provided a suitable environment for many alien species (9), but milk thistle is relatively unique in that it rapidly spread through the central valleys of California during the 1940's (10). Spreading in a short time to dominate a discontinuous habitat is a remarkable demonstration of adaptation for colonizing. The agricultural environment that was invaded had been dominated by alien annual weeds for 150 yr. For a species without vegetative propagation to invade a community of annuals underscores the competitive advantage of its germination characteristics.

(1)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York. (2)DiTomaso, J. M. and E. A. Healy. 2007. Weeds of California and Other Western States. ANR Publications. Oakland, CA. (3)Young, J. A., R. A. Evans and R. B. Hawkes. 1978. Milk Thistle (Silybum marianum) Seed Germination. Weed Science 26: 395-398.

3.04

(1)This plant occurs frequently in disturbed sites and is invasive because the large rosettes shade out native plants and form extensive patches that crowd out native vegetation and impede wildlife. (2)The Pampas region of South America is the site of one of the world's most important grasslands. These grasslands were invaded by S. marianum and by Cynara cardunculus, often called "cardoon." The two species, introduced from Eurasia, grow to great size in the Pampas and in favorable seasons may form an almost impenetrable plant cover over large areas (Darwin 1839, Hudson 1918). Even today, at several places in the world where infestations have gotten out of control, it is not uncommon to travel and farm and range roads with thickets of S. marianum towering to 3 to 4 m in height on either side.

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK. (2)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York.

3.05

(1)No other Silybum species listed as weeds anywhere

(1)http://www.hear.org/gcw/scientificnames/scinames.htm [Accessed 25 Mar 2009]

4.01

(1)A stout herb with glabrous to slightly pubescent stems of 20-250 cm height, and spiny-dentate leaves….Stem leaves are sessile, smaller and less deeply divided, with yellowish white spines up to 8 mm length…Involucral bracts are tapering into spines of 2-5 cm length.

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK.

4.02

(1)The rosettes commonly reach 1 m in diameter, coverage of the ground is complete and all plants beneath the mat are destroyed. When the thistle and its remains deteriorate, a large bare spot has been prepared for perhaps unwanted vegetation. (2)Variegate thistle is very competitive in pastures and, when well established, eliminates most other plants, including other thistle species by shading and competition for moisture and nutrients [not allelopathy] (3)There is no obvious allelopathic effect of S. marianum on the germination of other plants.

(1)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York. (2)Parsons, W.T. and E. G. Cuthbertson. 2001. Noxious weeds of Australia. CSIRO Publishing. Collingwood, Australia. (3)Gabay,R., U.Plitmann and A. Danin. 1994. Factors affecting the dominance of Silybum marianum L. (Asteraceae) in its specific habitats. Flora 189: 201-206.

4.03

(1)A stout herb with glabrous to slightly pubescent stems of 20-250 cm height, and spiny-dentate leaves

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK.

4.04

(1)poisononing of livestock as the result of feeding on S. marianum is not a special case of toxicity but instead is a routine problem that arises wherever animals are forced to or allowed to graze on species, sometimes crops, that accumulate high levels of nitrate. Stock animals normally have little interest in this formidable plant because of the tough, sharp spines on leaves and flowerheads. They will eat when the plant has been cut and wilted, or when it is standing after being sprayed with a hormone-like herbicide. At times of plant die-off in late summer and autumn, animals may be seed feeding on senescent leaves. If nitrogen is plentiful in the soil and the nitrate is high in the plant tissues the animals can be harmed. For the farmer who is uninformed of this there is a danger, and for those who appreciate the problem there is a dilemma, for if a range has a scattering of S. marianum or if his animals may suddenly break into dense patches of the thistle, there is a continuing decision that needs to be made about the quantity they should be allowed to ingest. In Australia, it is reported that the field cases of nitrate poisoning are very often in hungry livestock or among animals that are under the stress of mustering... (2)Goats readily eat the flower heads, and they have been used successfully by a number of landholders to reduce seed production which eventually has an effect on thistle populations.

(1)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York. (2)Parsons, W.T. and E. G. Cuthbertson. 2001. Noxious weeds of Australia. CSIRO Publishing. Collingwood, Australia.

4.05

(1)On occasion it is very high in nitrates and can be very toxic to stock animals…poisoning of livestock as the result of feeding on S. marianum is not a special case of toxicity but instead is a routine problem that arises wherever animals are forced to or allowed to graze on species, sometimes crops, that accumulate high levels of nitrate. Stock animals normally have little interest in this formidable plant because of the tough, sharp spines on leaves and flowerheads. They will eat when the plant has been cut and wilted, or when it is standing after being sprayed with a hormone-like herbicide. At times of plant die-off in late summer and autumn, animals may be seed feeding on senescent leaves. If nitrogen is plentiful in the soil and the nitrate is high in the plant tissues the animals can be harmed. For the farmer who is uninformed of this there is a danger, and for those who appreciate the problem there is a dilemma, for if a range has a scattering of S. marianum or if his animals may suddenly break into dense patches of the thistle, there is a continuing decision that needs to be made about the quantity they should be allowed to ingest. In Australia, it is reported that the field cases of nitrate poisoning are very often in hungry livestock or among animals that are under the stress of mustering...[nitrogen is not a toxin but management issue]

(1)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York.

4.06

(1)Not listed as an important alternate hose for plant pathogens [most mentions of pathogens deal with prospective biocontrol agents] (2)Silybum marianum (L.) Gaertn. (milk thistle) is a problematic invasive weed in the western United States. The rust fungus, Puccinia punctiformis (F. Strauss) Rohl., is found throughout the world as a pathogen of Cirsium arvense (L.) Scop. (Canadian thistle). Recently, plants of S. marianum grown from surface-disinfested seeds in our quarantine greenhouse were parasitized by a rust. Apparently, an isolate of P. punctiformis collected from C. arvense in Turkey that was present in the greenhouse had spread to adjacent S. marianum plants and caused infection without applying any artificial dew period. Ribosomal internal transcribed spacer region sequences from fungal spore DNA isolated from the two hosts were identical. Initial signs on S. marianum were abundant, fragrant spermogonia on large leaves. These signs occur on secondary shoots of C. arvense and are indicative of systemic fungal infection (1). As the fungus infection developed on S. marianum, uredinia and urediniospores were produced. Sori on older leaves also produced teliospores. Urediniospores from infected leaves were harvested and sprayed uniformly on eight 17-day-old plants of S. marianum grown in isolation from P. punctiformis. The spore suspension consisted of 4 mg urediniospores suspended in 40 ml distilled water. Inoculated plants were incubated for 18 h in a dew chamber at 20°C in the dark and transferred to a greenhouse (20 to 25°C, 30 to 50% relative humidity, and natural light). After 13 days, uredia with urediniospores developed on four of the plants. Using the same procedure, inoculations were repeated on plants of S. marianum and S. eburneum Coss. & Durieu (the only other species described in the genus) with urediniospores of a domestic isolate of the fungus from C. arvense in Maryland. Of 51 inoculated plants of S. marianum, 23 became infected and produced uredinia. None of the 12 inoculated plants of S. eburneum showed symptoms of infection. In nature, C. arvense and S. marianum occupy different ecological areas. C. arvense is found predominately in humid temperate habitats, while S. marianum is found in habitats with a dry Mediterranean climate. Life cycles of each host are also different. C. arvense is a perennial that emerges in spring and dies back in winter, while S. marianum is a winter annual that emerges in fall and dies in late spring. Because of the differences in life cycles combined with the different geographical distribution, P. punctiformis from C. arvense may rarely encounter susceptible S. marianum plants in the field. Since fungal spores can be produced routinely on artificially inoculated plants, there might be potential to use P. punctiformis for biological control of S. marianum. To our knowledge, this is the first report of S. marianum as a host for P. punctiformis.

(1)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York. (2)Berner, D. K., L. K. Paxson, W. L. Bruckart, D. G. Luster, M. McMahon, and J. L. Michael. 2002. First Report of Silybum marianum as a Host of Puccinia punctiformis. Plant Disease 86: 1271.

4.07

(1)Seeds contain silybin, a compound that stimulates liver tissue growth and is used as an antidote for poisoning by the death cap mushroom [Amanita phalloides]. Blessed milkthistle has been used medicinally for at least 2000 years. The young foliage, with prickles removed, is sometimes consumed as a salad green or cooked vegetable. (2)Edible Parts: Flowers; Leaves; Root; Stem. Edible Uses: Coffee; Oil.

(1)DiTomaso, J. M. and E. A. Healy. 2007. Weeds of California and Other Western States. ANR Publications. Oakland, CA. (2)http://pfaf.org/database/plants.php?Silybum+marianum [Accessed 25 Mar 2009]

4.08

(1)Fire hazards not among the many problems associated with this weed

(1)Parsons, W.T. and E. G. Cuthbertson. 2001. Noxious weeds of Australia. CSIRO Publishing. Collingwood, Australia.

4.09

(1)Shading discourages thistle seedlings by reducing their root growth and, therefore, their capacity to survive in competition with deep-rooted perennial species. (2)It cannot grow in the shade.

(1)Parsons, W.T. and E. G. Cuthbertson. 2001. Noxious weeds of Australia. CSIRO Publishing. Collingwood, Australia. (2)http://pfaf.org/database/plants.php?Silybum+marianum [Accessed 25 Mar 2009]

4.10

(1)oil pH requirements: 6.6 to 7.5 (neutral) 7.6 to 7.8 (mildly alkaline) 7.9 to 8.5 (alkaline) (2)Silybum marianum is mainly confined to high fertility soils. It frequently establishes on river flats, sheep camps, around stock yards and any other area of higher than normal soil nitrogen levels, especially if the area has been disturbed.

(1)http://davesgarden.com/guides/pf/go/1056/ [Accessed 25 Mar 2009] (2)Bean, C. 1985. ELEMENT STEWARDSHIP ABSTRACT for Silybum marianum. Available from http://tncinvasives.ucdavis.edu/esadocs/documnts/silymar.pdf [Accessed 25 Mar 2009]

4.11

(1)A stout herb with glabrous to slightly pubescent stems of 20-250 cm height, and spiny-dentate leaves

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK.

4.12

(1)This plant spread quickly once established and may form an impenetrable cover over large areas. (2)Charles Darwin (1898) provided one of the first and certainly one of the most vivid descriptions of a plant invasion at its zenith, the dominance of Silybum marianum (variegated thistle) in the Argentinean pampas by 1833. In recounting his overland journey from Bahia Blanca to Buenos Aires, he noted that "very many (probably several hundred) square miles are covered by one mass of these prickly plants, and are impenetrable to man or beast. Over the undulating plains, where these great beds occur, nothing else can now live."

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK. (2)Mooney, H. A., and R. J. Hobbs. 2000. Invasive species in a changing world. Island Press. Washington, D.C.

5.01

(1)Terrestrial

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK.

5.02

(1)Asteraceae

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK.

5.03

(1)Asteraceae

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK.

5.04

(1)S. marianum can propagate only by seeds, some of which may persist in the field as long as 10 yr.

(1)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York.

6.01

(1)It is a common weed in sheep areas of New Zealand and is regarded as weedy in South Africa, South America (Argentina and Brazil) and Afghanistan, and within its native range throughout Europe and Tunisia, Israel, Jordan and Iraq. [apparently not]

(1)Parsons, W.T. and E. G. Cuthbertson. 2001. Noxious weeds of Australia. CSIRO Publishing. Collingwood, Australia.

6.02

(1)Fruits are black achenes of 6-8 mm length and 2.5-4 mm width. The pappus is 15-20 mm long.

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK.

6.03

(1)2 species [unknown if hybridization occurs]

(1)Webb, C. J., W. R. Sykes, and P. J. Garnock-Jones. 1988. Flora of New Zealand Volume IV: Naturalized Pteridophytes, Gymnosperms, Dicotyledons. Botany Division, D.S.I.R. Christchurch, New Zealand.

6.04

(1)Studies carried on the biology of Silybum marianum Gaertn. in years 1982-87 in moderate climatic conditions made it possible to determine the duration of germination, development of basal leaves, blooming and fructifying process. The process of blooming of capitular inflorescences in natural and artificial self-pollination conditions showed that milk thistle protects itself against self-pollination (protandry) but it is not self-sterile. The colour of involucre depends on the meteorological conditions in the fructifying stage: when the weather is cool and rainy many seeds do not colour at all. [unlikely to become self-pollinated but not self-incompatible]

(1)Czabajska, W., K. Kazimierczak, and E. Maciolkowska-Ludowicz.1989. Studies on the biology of Silybum marianum Gaertn. Pt. 1. Development, blooming and fructifying. Herba Polonica 35(2-3): 109-115.

6.05

(1)The plant is of some value to the honey industry because the flowers provide a useful source of pollen in early summer. (2)The flowers are hermaphrodite (have both male and female organs) and are pollinated by Bees. (3)Reduction in seed set after removal of honey bees may not occur as predicted for some other exotic weeds since they are also frequently visited by diverse guilds of native bees. Examples may include Asteraceae: Centaurea solstitialis, Cichorium intybus L., and Silybum marianum (L.) Gaertn.;

(1)Parsons, W.T. and E. G. Cuthbertson. 2001. Noxious weeds of Australia. CSIRO Publishing. Collingwood, Australia. (2)http://pfaf.org/database/plants.php?Silybum+marianum [Accessed 25 Mar 2009] (3)Thorp, R. W. Adrian M. Wenner, and John F. Barthell. 1999. POLLEN AND NECTAR RESOURCE OVERLAP AMONG BEES ON SANTA CRUZ ISLAND. 5th California Islands Symposium: 261-268.

6.06

(1)S. marianum can propagate only by seeds, some of which may persist in the field as long as 10 yr.

(1)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York.

6.07

(1)S. marianum is an erect annual or biennial to 3 m or more, commonly 1 to 2 m

(1)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York.

7.01

(1)Seeds are dispersed by attaching to animals, by water and in mud.

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK.

7.02

(1)The weed is spread by natural means, by transport vehicles, including farm equipment, by animals, with movement of hay, in mud and water, by accident on sacks and other articles of commerce, and sometimes with intent to use the species for folk remedies or other medical purposes.

(1)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York.

7.03

(1)In 1851, in Australia, this species was subject of the first legislation against noxious weeds in that country…In Tasmania, it is found in feed grains offered to stock animals and in low-grade, uncertified cropseed supplies. Here it is one of the species whose seeds are "prohibited" in the standards for certified pasture seed.

(1)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York.

7.04

(1)seeds and pappus may vary in size, and where latter is large enough the seed may be carried some distance by the wind…The seeds are large and have a small pappus, so that many are found within a few meteres of the parent plant, thus giving rise to dense local stands (2)Seeds probably disperse only short distances with wind

(1)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York. (2)DiTomaso, J. M. and E. A. Healy. 2007. Weeds of California and Other Western States. ANR Publications. Oakland, CA.

7.05

(1)Seeds are dispersed by attaching to animals, by water and in mud.

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK.

7.06

(1)Variegated thistle seeds are large and palatable and are eaten by birds and rodents. Evidence of this was observed at all sites. In spite of these losses, large seed banks were maintained at all sites. [birds and rodents are seed predators, not dispersers]

(1)Bruzzese, E. and K. Turnbull. 1996. Ecology of Cirsium vulgare and Silybum marianum in relation to biological control. Plant Protection Quarterly 11(Supplement 2): 245-249.

7.07

(1)Seeds are dispersed by attaching to animals, by water and in mud. (2)S. marianum is a common ruderal plant in Israel, where it is adapted to a life of association with the harvesting-ant Messor semirufus. An oil body (an elaiosome) at the tip of the achene attracts the ants and they carry the seeds to the protection of their nests. Later they are carried out and planted with refuse from the nests (dead ants, grains, soil, other plant parts). Rain water and nutrients in the refuse stimulate early establishment of plants that become much larger and produce more seed heads than plants in a control area.

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK. (2)Holm, L. G., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World weeds: natural histories and distribution. John Wiley and Sons. New York.

7.08

(1)Variegated thistle seeds are large and palatable and are eaten by birds and rodents. Evidence of this was observed at all sites. In spite of these losses, large seed banks were maintained at all sites. [birds and rodents are seed predators, not dispersers]

(1)Bruzzese, E. and K. Turnbull. 1996. Ecology of Cirsium vulgare and Silybum marianum in relation to biological control. Plant Protection Quarterly 11(Supplement 2): 245-249.

8.01

(1)Precise figures on seed pro- production for milk thistle are not available. We do know that seeds average 0.02 g in weight, about 50 seeds are produced per terminal head, and 10 to 50 heads are produced per plant. From this we can calculate 10 to 50 g of seed produced per plant. With a conservative average density of 2 plants/mi2 theoretical seed production reaches 100 to 500 kg/ha. (2)Seed banks ranged from 2111 to 6058 seeds m-2.

(1)Young, J. A., R. A. Evans and R. B. Hawkes. 1978. Milk Thistle (Silybum marianum) Seed Germination. Weed Science 26: 395-398. (2)Bruzzese, E. and Keith Turnbull. 1996. Ecology of Cirsium vulgare and Silybum marianum in relation to biological control. Plant Protection Quarterly 11(Supplement 2): 245-249.

8.02

(1)Seeds may remain viable for 10 years.

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK.

8.03

(1)Chemical control is most effective at the seedling and rosette stages. An effective herbicide is 2,4-D ester. Planting desirable species suppresses seedling establishment of this plant. (2)Variegated thistle is susceptible to several herbicides. It is most readily killed in the seedling and rosette stages, becoming more resistant as plants mature. Herbicides containing 2,4-D or MCPA are effective, but in New Zealand, MCPA is generally preferred. Because seeds germinate over several months and autumn spraying kills only those plants which have emerged, a further spraying is necessary to kill those germinating in later winter-early spring.

(1)Weber, E. 2003. Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. CABI Publishing. Wallingford, UK. (2)Parsons, W.T. and E. G. Cuthbertson. 2001. Noxious weeds of Australia. CSIRO Publishing. Collingwood, Australia.

8.04

(1)Cultivation can control seedlings. Mowing mature plants before flowers open can help control stands. Burning can encourage seed germination and establishment [benefits from fire, but is suppressed by cultivation and mowing]

(1)DiTomaso, J. M. and E. A. Healy. 2007. Weeds of California and Other Western States. ANR Publications. Oakland, CA.

8.05

(1)The seedhead weevil (Rhinocyllus conicus) was released in 1971 in southern California as a biocontrol agent for blessed milkthistle, but control has been poor to date. In addition, the weevil attacks several native thistle species. [probably no natural enemies in Hawaii, but unknown at this point]

(1)DiTomaso, J. M. and E. A. Healy. 2007. Weeds of California and Other Western States. ANR Publications. Oakland, CA.


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