Cotton thistle
Encyclopedia
Onopordum acanthium is a flowering plant
in the family Asteraceae
. It is native to Europe
and Western Asia from the Iberian Peninsula
east to Kazakhstan
, and north to central Scandinavia
, and widely naturalised
elsewhere. It is a vigorous biennial plant
with coarse, spiny leaves and conspicuous spiny-winged stems.
Cotton Thistle is a biennial plant
, producing a large rosette
of spiny leaves
the first year. The plants typically germinate in the autumn after the first rains and exist as rosettes throughout the first year, forming a stout, fleshy taproot
that may extend down 30 cm or more for a food reserve.
In the second year, the plant grows (0.2–) 0.5–2.5 (–3) m tall and a width of 1.5 m. The leaves are 10–50 cm wide, are alternate and spiny, often covered with white woolly hairs and with the lower surface more densely covered than the upper. The leaves are deeply lobed with long, stiff spines along the margins. Fine hairs give the plant a greyish appearance. The massive main stem may be 10 cm wide at the base, and is branched in the upper part. Each stem shows a vertical row of broad, spiny wings (conspicuous ribbon-like leafy material), typically 2–3 cm wide, extending to the base of the flower head.
The flower
s are globe shaped, 2–6 cm in diameter, from dark pink to lavender, and are produced in the summer. The flower buds form first at the tip of the stem and later at the tip of the axillary branches. They appear singly or in groups of two or three on branch tips. The plants are androgynous, with both pistil
and stamen
s, and sit above numerous, long, stiff, spine-tipped bract
s, all pointing outwards, the lower ones wider apart and pointing downwards. After flowering, the ovary
starts swelling and forms about 8,400 to 40,000 seeds per plant.
with dry summers, such as the Mediterranean region, growing best in sandy, sandy clay and calcareous soil
s which are rich in ammonium
salts. It grows in ruderal
places, as well as dry pastures and disturbed fields. Its preferred habitats are natural areas, disturbed sites, roadsides, fields, and especially sites with fertile soils, agricultural areas, range/grasslands, riparian zones, scrub/shrublands valleys and plains along with water courses. Temperature and moisture, rather than soil nutrient concentrations determine the ecological performance of Onopordum species.
In Europe, the plant tends to colonize disturbed pastures. In its native range, Cotton Thistle is considered a weak competitor that needs regeneration gaps to develop and maintain stands; populations tend to retreat when disturbance ceases. The plant has been widely introduced at mid-latitudes across much of North America.
Cotton Thistle can spread rapidly. For example, it was first found in Utah in 1963. By 1981, it covered approximately 6070 hectares in 17 counties. Eight years later, it had spread to cover more than 22,540 hectares in 22 counties.
for at least seven years and possibly for up to twenty years or more. Yearly seed production and seed dormancy
are highly variable depending on environmental conditions. The slender and smooth achenes are about 3 mm long and are brown with gray markings. They are tipped with a pappus of slender bristles. Mainly locally dispersed by wind, or more widely by humans, birds, wildlife, livestock or streams, the seeds are sensitive to light and only germinate when close to the surface. Seedlings will emerge from soil depths up to 4.5 cm, with 0.5 cm being optimal. While some seeds will germinate in the dark, studies indicate that most germination occurs with alternating light/dark cycles, with 8 hours being the optimal day length.
The leaves of Cotton Thistle provide food for the caterpillar
s of some Lepidoptera
, such as the Thistle Ermine (Myelois circumvoluta).
The botanical name is derived from the Ancient Greek
words onos (donkey), perdo (to consume), and acanthos (thorn), meaning 'thorny donkey food'.
The common name of Cotton Thistle derives from the cotton
-like hairs on the leaves. Other names include Scots thistle or Scottish thistle, heraldic thistle and woolly thistle; the name Scots thistle comes from its status as the national emblem
of Scotland
.
for its bold foliage and large flowers. It has been used to treat cancers and ulcers and to diminish discharges of mucous membranes. The receptacle was eaten in earlier times like an artichoke. The cottony hairs on the stem have been occasionally collected to stuff pillows. Oil from the seeds has been used for burning and cooking.
, South America
, and Australia
as an ornamental plant, and is now considered a major agricultural and wildland noxious weed
. It has been recorded from nearly 50 countries. It is difficult to eradicate because of its drought resistance. It can spread rapidly and eventually dense stands prohibit foraging by livestock
. Infestations of Cotton Thistle often start in disturbed areas such as roadways, campsites, burned areas, and ditch banks. The weed adapts best to areas along rivers and streams, but can be a serious problem in pastures, grain fields and range areas. A single Cotton Thistle is imposing enough, but an entire colony can ruin a pasture
or destroy a park or campsite, sometimes forming tall, dense, impenetrable stands. Besides creating an impenetrable barrier to humans and animals, Cotton Thistle nearly eliminates forage use by livestock
and some mammal species such as deer
and elk
.
Known infestations include most of the Pacific Northwest along with Utah, Colorado, New Mexico, Wyoming, Nebraska, and South Dakota. On western rangeland, infestations directly result in significant economic losses for ranchers. It is also widespread in Australia and New Zealand. In Australia it commonly hybridises with the related invasive Illyrian Thistle Onopordum illyricum
.
Small infestations may be physically removed or cut a few centimetres below the soil surface ensuring that no leaves remain attached to prevent regrowth. Mowing during early flowering will not kill the plant but will reduce seed production. Repeated treatments may be required because populations typically exhibit a wide range of developmental stages among individual plants. Slashing should be done prior to flowering since seed may mature in the seed head after cutting. Plants should not be mowed following seed set, as this increases chances for seed dispersal.
Chemical
Because of their shorter life cycle, Cotton Thistle plants can be effectively treated with herbicides. All herbicide treatments should be applied at the rosette stage of the plant. Generally, herbicide applications would be in early spring or autumn. One of the primary difficulties in chemical control of Cotton Thistles is their ability to germinate nearly year round. From autumn to spring a range of plant sizes can be found which may result in variable success from chemical control. Herbicides are very effective on seedlings and young rosettes, but control becomes more variable with increasing plant age. Onopordum spp. seeds may persist for several years in the soil. Buried seed may persist for up to twenty years, and reinfestation is likely without yearly management. Therefore several years of re-treatment may be necessary. Picloram, dicamba, 2,4-D, dicamba + 2,4,-D, and metsulfuron are effective for controlling Cotton Thistle. Clopyralid is more selective for controlling plants in the Asteraceae family, but will also injure or kill legumes.
Biological
There are no biological control agents that have been specifically released for Cotton Thistle control in the United States
. A thistle head weevil (Rhinocyllus conicus
) that feeds on Italian Thistle (Carduus pycnocephalus
) has also been shown to feed on Cotton thistle. However, this insect was the object of imprudent biological control introduction, and it became an invasive species that has threatened endangered native thistles in North America (Strong 1997). Establishment of this thistle head weevil as a biological control agent for Cotton thistle has been unsuccessful in the Pacific Northwest. A thistle crown weevil (Trichosirocalus horridus
) that feeds on Musk, Bull, Plumeless, Italian, and Creeping Thistles will also feed on Cotton Thistle. In Australia, this insect has been shown to kill Cotton Thistle rosettes. The related Trichosirocalus briese is also being tested as a control agent.
In Australia, a total of seven insects have been released to control Cotton thistle. Two of the seven released insects are weevil
s, including Larinus latus
which feeds on the seeds, and Lixus cardui
, which bores in the stems.
Integrated management
A combination of methods (IPM) is often more effective than any single method. An integrated pest management plan deals with prevention as well as control. Eradication of weed species is often not a practical goal, but in many cases reducing infestation to manageable levels is an achievable objective. Seed bank longevity is a major factor in managing Cotton Thistles. Re-establishing competitive perennial grasses and monitoring infested areas on a yearly basis is critical. Herbicides can successfully be used for reducing thistle populations and giving grasses a competitive advantage. However, they cannot be used as a stand alone solution. These techniques must be linked with good grazing practices in rangeland areas. Otherwise, the thistles will recolonize and rapidly replenish the seed bank to pre-control levels.
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
in the family Asteraceae
Asteraceae
The Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...
. It is native to Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and Western Asia from the Iberian Peninsula
Iberian Peninsula
The Iberian Peninsula , sometimes called Iberia, is located in the extreme southwest of Europe and includes the modern-day sovereign states of Spain, Portugal and Andorra, as well as the British Overseas Territory of Gibraltar...
east to Kazakhstan
Kazakhstan
Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...
, and north to central Scandinavia
Scandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...
, and widely naturalised
Naturalisation (biology)
In biology, naturalisation is any process by which a non-native organism spreads into the wild and its reproduction is sufficient to maintain its population. Such populations are said to be naturalised....
elsewhere. It is a vigorous biennial plant
Biennial plant
A biennial plant is a flowering plant that takes two years to complete its biological lifecycle. In the first year the plant grows leaves, stems, and roots , then it enters a period of dormancy over the colder months. Usually the stem remains very short and the leaves are low to the ground, forming...
with coarse, spiny leaves and conspicuous spiny-winged stems.
Description
Biennial plant
A biennial plant is a flowering plant that takes two years to complete its biological lifecycle. In the first year the plant grows leaves, stems, and roots , then it enters a period of dormancy over the colder months. Usually the stem remains very short and the leaves are low to the ground, forming...
, producing a large rosette
Rosette (botany)
In botany, a rosette is a circular arrangement of leaves, with all the leaves at a single height.Though rosettes usually sit near the soil, their structure is an example of a modified stem.-Function:...
of spiny leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
the first year. The plants typically germinate in the autumn after the first rains and exist as rosettes throughout the first year, forming a stout, fleshy taproot
Taproot
A taproot is an enlarged, somewhat straight to tapering plant root that grows vertically downward. It forms a center from which other roots sprout laterally.Plants with taproots are difficult to transplant...
that may extend down 30 cm or more for a food reserve.
In the second year, the plant grows (0.2–) 0.5–2.5 (–3) m tall and a width of 1.5 m. The leaves are 10–50 cm wide, are alternate and spiny, often covered with white woolly hairs and with the lower surface more densely covered than the upper. The leaves are deeply lobed with long, stiff spines along the margins. Fine hairs give the plant a greyish appearance. The massive main stem may be 10 cm wide at the base, and is branched in the upper part. Each stem shows a vertical row of broad, spiny wings (conspicuous ribbon-like leafy material), typically 2–3 cm wide, extending to the base of the flower head.
The flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s are globe shaped, 2–6 cm in diameter, from dark pink to lavender, and are produced in the summer. The flower buds form first at the tip of the stem and later at the tip of the axillary branches. They appear singly or in groups of two or three on branch tips. The plants are androgynous, with both pistil
Gynoecium
Gynoecium is most commonly used as a collective term for all carpels in a flower. A carpel is the ovule and seed producing reproductive organ in flowering plants. Carpels are derived from ovule-bearing leaves which evolved to form a closed structure containing the ovules...
and stamen
Stamen
The stamen is the pollen producing reproductive organ of a flower...
s, and sit above numerous, long, stiff, spine-tipped bract
Bract
In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis, or cone scale. Bracts are often different from foliage leaves. They may be smaller, larger, or of a different color, shape, or texture...
s, all pointing outwards, the lower ones wider apart and pointing downwards. After flowering, the ovary
Ovary (plants)
In the flowering plants, an ovary is a part of the female reproductive organ of the flower or gynoecium. Specifically, it is the part of the pistil which holds the ovule and is located above or below or at the point of connection with the base of the petals and sepals...
starts swelling and forms about 8,400 to 40,000 seeds per plant.
Distribution and habitat
Cotton Thistle is native to Europe and Asia. The plant prefers habitatsHabitat (ecology)
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...
with dry summers, such as the Mediterranean region, growing best in sandy, sandy clay and calcareous soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
s which are rich in ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
salts. It grows in ruderal
Ruderal species
A ruderal species is a plant species that is first to colonize disturbed lands. The disturbance may be natural , or due to human influence – constructional , or agricultural .Ruderal species typically dominate the disturbed area...
places, as well as dry pastures and disturbed fields. Its preferred habitats are natural areas, disturbed sites, roadsides, fields, and especially sites with fertile soils, agricultural areas, range/grasslands, riparian zones, scrub/shrublands valleys and plains along with water courses. Temperature and moisture, rather than soil nutrient concentrations determine the ecological performance of Onopordum species.
In Europe, the plant tends to colonize disturbed pastures. In its native range, Cotton Thistle is considered a weak competitor that needs regeneration gaps to develop and maintain stands; populations tend to retreat when disturbance ceases. The plant has been widely introduced at mid-latitudes across much of North America.
Cotton Thistle can spread rapidly. For example, it was first found in Utah in 1963. By 1981, it covered approximately 6070 hectares in 17 counties. Eight years later, it had spread to cover more than 22,540 hectares in 22 counties.
Ecology
Cotton Thistle reproduces only by seeds. Most seeds germinate in autumn after the first rains, but some seeds can germinate year round under favourable moisture and temperature conditions. Seeds that germinate in late autumn become biennials. But when they germinate earlier, they can behave as annuals. Buried seed can remain viable in the soil seed bankSoil Seed Bank
The soil seed bank refers to the natural storage of seeds, often dormant, within the soil of most ecosystems. The study of soil seed banks started in 1859 when Charles Darwin observed the emergence of seedlings using soil samples from the bottom of a lake. The first scientific paper on the subject...
for at least seven years and possibly for up to twenty years or more. Yearly seed production and seed dormancy
Seed dormancy
Seed dormancy is a condition of plant seeds that prevents germination when the seeds are under optimal environmental conditions for germination. Living, non dormant seeds germinate when soil temperatures and moisture conditions are suited for cellular processes and division; dormant seeds do...
are highly variable depending on environmental conditions. The slender and smooth achenes are about 3 mm long and are brown with gray markings. They are tipped with a pappus of slender bristles. Mainly locally dispersed by wind, or more widely by humans, birds, wildlife, livestock or streams, the seeds are sensitive to light and only germinate when close to the surface. Seedlings will emerge from soil depths up to 4.5 cm, with 0.5 cm being optimal. While some seeds will germinate in the dark, studies indicate that most germination occurs with alternating light/dark cycles, with 8 hours being the optimal day length.
The leaves of Cotton Thistle provide food for the caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...
s of some Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
, such as the Thistle Ermine (Myelois circumvoluta).
Taxonomy and naming
Three subspecies are accepted:- Onopordum acanthium subsp. acanthium. Most of the species' range.
- Onopordum acanthium subsp. gautieri (Rouy) Franco. France, Spain.
- Onopordum acanthium subsp. parnassicum (Boiss. & Heldr.) Nyman. Greece.
The botanical name is derived from the Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
words onos (donkey), perdo (to consume), and acanthos (thorn), meaning 'thorny donkey food'.
The common name of Cotton Thistle derives from the cotton
Cotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective capsule, around the seeds of cotton plants of the genus Gossypium. The fiber is almost pure cellulose. The botanical purpose of cotton fiber is to aid in seed dispersal....
-like hairs on the leaves. Other names include Scots thistle or Scottish thistle, heraldic thistle and woolly thistle; the name Scots thistle comes from its status as the national emblem
National emblem
A national emblem symbolically represents a nation. Most national emblems originate in the natural world, such as animals or birds, but another object may serve. National emblems may appear on many things such as the national flag, coat of arms, or other patriotic materials...
of Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
.
Uses
Cotton Thistle is grown as an ornamental plantOrnamental plant
Ornamental plants are plants that are grown for decorative purposes in gardens and landscape design projects, as house plants, for cut flowers and specimen display...
for its bold foliage and large flowers. It has been used to treat cancers and ulcers and to diminish discharges of mucous membranes. The receptacle was eaten in earlier times like an artichoke. The cottony hairs on the stem have been occasionally collected to stuff pillows. Oil from the seeds has been used for burning and cooking.
Cotton Thistle as an invasive species
In the late 19th century, it was introduced to temperate regions of North AmericaNorth America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, and Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
as an ornamental plant, and is now considered a major agricultural and wildland noxious weed
Weed
A weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More specifically, the term is often used to...
. It has been recorded from nearly 50 countries. It is difficult to eradicate because of its drought resistance. It can spread rapidly and eventually dense stands prohibit foraging by livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...
. Infestations of Cotton Thistle often start in disturbed areas such as roadways, campsites, burned areas, and ditch banks. The weed adapts best to areas along rivers and streams, but can be a serious problem in pastures, grain fields and range areas. A single Cotton Thistle is imposing enough, but an entire colony can ruin a pasture
Pasture
Pasture is land used for grazing. Pasture lands in the narrow sense are enclosed tracts of farmland, grazed by domesticated livestock, such as horses, cattle, sheep or swine. The vegetation of tended pasture, forage, consists mainly of grasses, with an interspersion of legumes and other forbs...
or destroy a park or campsite, sometimes forming tall, dense, impenetrable stands. Besides creating an impenetrable barrier to humans and animals, Cotton Thistle nearly eliminates forage use by livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...
and some mammal species such as deer
Red Deer
The red deer is one of the largest deer species. Depending on taxonomy, the red deer inhabits most of Europe, the Caucasus Mountains region, Asia Minor, parts of western Asia, and central Asia. It also inhabits the Atlas Mountains region between Morocco and Tunisia in northwestern Africa, being...
and elk
Moose
The moose or Eurasian elk is the largest extant species in the deer family. Moose are distinguished by the palmate antlers of the males; other members of the family have antlers with a dendritic configuration...
.
Known infestations include most of the Pacific Northwest along with Utah, Colorado, New Mexico, Wyoming, Nebraska, and South Dakota. On western rangeland, infestations directly result in significant economic losses for ranchers. It is also widespread in Australia and New Zealand. In Australia it commonly hybridises with the related invasive Illyrian Thistle Onopordum illyricum
Onopordum illyricum
Onopordum illyricum is a species of thistle known by the common name Illyrian thistle, or Illyrian cottonthistle. It is native to southestern Europe, but has been introduced into Australia and California, where it has become a noxious weed....
.
Control
MechanicalSmall infestations may be physically removed or cut a few centimetres below the soil surface ensuring that no leaves remain attached to prevent regrowth. Mowing during early flowering will not kill the plant but will reduce seed production. Repeated treatments may be required because populations typically exhibit a wide range of developmental stages among individual plants. Slashing should be done prior to flowering since seed may mature in the seed head after cutting. Plants should not be mowed following seed set, as this increases chances for seed dispersal.
Chemical
Because of their shorter life cycle, Cotton Thistle plants can be effectively treated with herbicides. All herbicide treatments should be applied at the rosette stage of the plant. Generally, herbicide applications would be in early spring or autumn. One of the primary difficulties in chemical control of Cotton Thistles is their ability to germinate nearly year round. From autumn to spring a range of plant sizes can be found which may result in variable success from chemical control. Herbicides are very effective on seedlings and young rosettes, but control becomes more variable with increasing plant age. Onopordum spp. seeds may persist for several years in the soil. Buried seed may persist for up to twenty years, and reinfestation is likely without yearly management. Therefore several years of re-treatment may be necessary. Picloram, dicamba, 2,4-D, dicamba + 2,4,-D, and metsulfuron are effective for controlling Cotton Thistle. Clopyralid is more selective for controlling plants in the Asteraceae family, but will also injure or kill legumes.
Biological
There are no biological control agents that have been specifically released for Cotton Thistle control in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. A thistle head weevil (Rhinocyllus conicus
Rhinocyllus conicus
Rhinocyllus conicus is a species of true weevil. It is best known as a controversial agent of biological pest control which has been used against noxious thistles in the genera Carduus, Cirsium, Onopordum, and Silybum....
) that feeds on Italian Thistle (Carduus pycnocephalus
Carduus pycnocephalus
Carduus pycnocephalus is a species of thistle native to the Mediterranean region of Europe and Asia which has become a noxious weed in Australia, New Zealand, South Africa, South America, and North America, especially in California, where it is a C-listed weed by...
) has also been shown to feed on Cotton thistle. However, this insect was the object of imprudent biological control introduction, and it became an invasive species that has threatened endangered native thistles in North America (Strong 1997). Establishment of this thistle head weevil as a biological control agent for Cotton thistle has been unsuccessful in the Pacific Northwest. A thistle crown weevil (Trichosirocalus horridus
Trichosirocalus horridus
Trichosirocalus horridus is a species of true weevil, native to Europe. It is a biological pest control agent that was introduced into the United States in 1974 to control exotic thistles, especially in the Cirsium and Carduus genera....
) that feeds on Musk, Bull, Plumeless, Italian, and Creeping Thistles will also feed on Cotton Thistle. In Australia, this insect has been shown to kill Cotton Thistle rosettes. The related Trichosirocalus briese is also being tested as a control agent.
In Australia, a total of seven insects have been released to control Cotton thistle. Two of the seven released insects are weevil
Weevil
A weevil is any beetle from the Curculionoidea superfamily. They are usually small, less than , and herbivorous. There are over 60,000 species in several families, mostly in the family Curculionidae...
s, including Larinus latus
Larinus latus
Larinus latus is a species of true weevil. It is used as an agent of biological pest control against Onopordum thistles in Australia....
which feeds on the seeds, and Lixus cardui
Lixus cardui
Lixus cardui is a species of true weevil found in EuropeIt was introduced in Australia to control scotch thistle Onopordum acanthium, an invasive weed....
, which bores in the stems.
Integrated management
A combination of methods (IPM) is often more effective than any single method. An integrated pest management plan deals with prevention as well as control. Eradication of weed species is often not a practical goal, but in many cases reducing infestation to manageable levels is an achievable objective. Seed bank longevity is a major factor in managing Cotton Thistles. Re-establishing competitive perennial grasses and monitoring infested areas on a yearly basis is critical. Herbicides can successfully be used for reducing thistle populations and giving grasses a competitive advantage. However, they cannot be used as a stand alone solution. These techniques must be linked with good grazing practices in rangeland areas. Otherwise, the thistles will recolonize and rapidly replenish the seed bank to pre-control levels.
External links
- Species Profile- Scotch Thistle (Onopordum acanthium), National Invasive Species Information Center, United States National Agricultural LibraryUnited States National Agricultural LibraryThe United States National Agricultural Library is one of the world's largest agricultural research libraries, and serves as a National Library of the United States and as the library of the United States Department of Agriculture...
. Lists general information and resources for Cotton Thistle.