Starthistle, Yellow


Pest Information
Common Name: Starthistle, Yellow
Family Name: Asteraceae (Sunflower Family)
Latin Name: Centaurea solstitialis L.
Other Names: Yellow star thistle, geeldissel, golden star thistle, St. Barnaby's thistle, yellow centaury, yellow cockspur
Provincial Designation: Prohibited noxious
Seed Act Designation: Prohibited noxious
Life Cycle: Annual, Winter Annual
Mode of Spread: Seed

Detailed Information
Provincial Situation: In North America, yellow starthistle occurs in at least 41 of 50 US states and potentially in 4 Canadian provinces (AB, MB, SK & ON). Infestations are especially heavy in California where they cover more area than those in all other US states combined (about 17% of California’s total land base is estimated as infested). Alberta is suspected to have sporadic plants at US border edges.
Description:

Yellow starthistle stems are stiff and erect and grows up to 2m in height. Stems are usually openly branched. Yellow starthistle produces deeply lobed rosette leaves with pointed tips that lie close to the ground. Lower leaves are 5-15 cm long, and progressively smaller up the stem. Upper leaves are 1-3 cm long, narrow, and densely covered with cobwebby hairs later in the season.

Yellow starthistle inflorescences are borne in solitary flowerheads on stem tips, although vigorous plants may produce flowerheads in branch axils. The involucres (basket like recepticale) is about 1.2-1.8 cm long. Phyllaries(bracts) have 1 long central spine 1.0-2.5 cm long and 2 or more pairs of short lateral spines and are densely to sparsely covered with hairs. Yellow starthistle fruits are achenes of 2 types, both glabrous and about 2 to 3 mm long. Most of the seeds (75-90%) have a short (2-5 mm), stiff pappus (plumed). Seeds around the outside of the flowerhead are darker in color and have no pappus (plumeless).

Yellow starthistle has a large taproot that grows to soil depths of 1 m or more, providing drought tolerance. Hairs and waxy coating on mature yellow starthistle leaves reflect light, thus reducing the heat load and transpiration demand, while winged stems also dissipate heat. These qualities, along with deep roots, allow yellow starthistle to thrive under full sunlight in hot, dry conditions. Mycorrhizal fungi have been observed on yellow starthistle plants.

Once established, yellow starthistle can survive at high population densities, with estimates of 2 to 3 million plants per acre (5-7.5 million per hectare) reported. This dense cover reduces sunlight penetration to the soil surface, inhibiting germination and development of competing vegetation. Old yellow starthistle stalks are persistent and usually remain standing through the winter.

Key Characteristics:

 Rosette leaves deeply lobed margins with pointed tips
 Winged stems
 Cottony pubescence late in season
 Yellow flowers, solitary, and have ¾ inch long thorn like bracts

Similar Species: Malta starthistle (Centaurea melitensis) has smaller seed heads with reduced spines which are branched at base. http://calphotos.berkeley.edu/cgi/img_query?query_src=photos_index&where-taxon=Centaurea+melitensis
Purple starthistle (Centaurea calcitrapa) upper leaves do not form a wing down stem and flowers are purple.
http://calphotos.berkeley.edu/cgi/img_query?where-genre=Plant&where-taxon=Centaurea+calcitrapa
Where it Grows (Habitat & Ecology): The Yellow star-thistle plant has the ability to create monotypic stands and habitats in the cultivated soil of fields, graded dirt sites, and disturbed natural ecosystem lands. Its colonization eliminates and prevents other plant species from growing terminating the habitat's biodiversity. Extensive spreading monotypic fields of yellow starthistle are not uncommon. Its growth plasticity, competitiveness, preference for the Mediterranean climate, and a lack of natural herbivore enemies and co-evolved species, make it a very successful invader. The plant is an invasive pest in field crops, degrades native plant habitats and natural ecosystems, prevents the grazing of domestic animals in rangelands, and is a physical barrier to indigenous animal movement in wildlands
How it Spreads (Mode of Spread):

Since Yellow starthistle is a winter annual it relies on abundant seed production for spread. Distribution of yellow starthistle seedlings is predominantly in and near the previous year's yellow starthistle debris, which suggests a slow rate of spread.

Yellow starthistle produces two types of seed plumeless and plumed. Which takes care of the reseeding the area of the initial plant via plumeless and encouraging new plants in the near vicinity via the plumed. The size of the pappus on plumed seeds is small relative to seed size and wind moves seeds only short distances, roughly equal to the height of the plant. Plumed seeds are usually dispersed soon after flowers senesce and drop their petals. Plumeless seeds are usually retained in the seedhead until the spiny bracts fall off (about a month), but can be retained well into winter

The pappus bristles are covered with stiff, microscopic barbs that readily adhere to clothing and hair. Long-distance dispersal of yellow starthistle seed is often directly related to human activities and occurs by movement of livestock, vehicles, equipment, and contaminated hay and crop seed. Birds such as ring-necked pheasants American goldfinches feed heavily on yellow starthistle seeds contributing to spread.

Reproduction (Dispersal):

Since Yellow starthistle is a winter annual it relies on abundant seed production for spread. Distribution of yellow starthistle seedlings is predominantly in and near the previous year's yellow starthistle debris, which suggests a slow rate of spread.

Economic Importance (Beneficial Aspects): Yellow starthistle is regarded as an important honey source plant in California and other western states. Yellow starthistle is used in Turkish folk medicine for the treatment of ulcers. In a laboratory study, aqueous extracts of fresh or dried flowers of yellow starthistle given orally showed significant (p<0.01) anti-ulcerogenic activity in rats.
Toxicity and Other Concerns: Yellow star-thistle is a plant toxic to horses, causing chewing disease (Nigropallidal encephalomalacia). It has been suggested by several researchers that yellow starthistle might have an allelopathic effect on surrounding vegetation; however, there is no direct evidence to substantiate that claim.
Origin:

Yellow starthistle is native to southern Europe and western Eurasia.

Seed Production:

Plants can produce 1 to 1,000 flowerheads per plant and 30 to 80 seeds per flowerhead. Large plants can produce nearly 75,000 seeds.
European honeybees are an important pollinator of yellow starthistle and may be responsible for over half of seed set. Bumblebees are also important floral visitors, and several other insects contribute to the fertilization of yellow starthistle.
Yellow starthistle seed may remain viable in the soil for as long as 10 years.
Over 90% of yellow starthistle seeds are germinable 1 week after seed dispersal.
No germinable seeds are present until 2% of spiny heads initiate flowering. The time from flower initiation to the development of mature viable seed is about 8 days. Seed production increases exponentially as percent flowering progresses, and by 10% flowering, an estimated 100 germinable seeds are produced per 100 flowerheads.

Dispersal How it spreads Since Yellow starthistle is a winter annual it relies on abundant seed production for spread. Distribution of yellow starthistle seedlings is predominantly in and near the previous year's yellow starthistle debris, which suggests a slow rate of spread.

Yellow starthistle produces two types of seed plumeless and plumed. Which takes care of the reseeding the area of the initial plant via plumeless and encouraging new plants in the near vicinity via the plumed. The size of the pappus on plumed seeds is small relative to seed size and wind moves seeds only short distances, roughly equal to the height of the plant. Plumed seeds are usually dispersed soon after flowers senesce and drop their petals. Plumeless seeds are usually retained in the seedhead until the spiny bracts fall off (about a month), but can be retained well into winter

Cultural Control: Manual removal (hand-pulling or digging) of yellow starthistle is most effective when small patches or scattered plants are detected before they produce a crop of seeds. Hand-pulling can be an important option in steep or uneven terrain where other mechanical tools are impossible to use, and is useful along rivers and riparian zones. To ensure that plants do not recover, it is important to detach all aboveground stem material. A 2-inch piece of the stem can recover if leaves and buds are still attached.
The best time to pull yellow starthistle is after plants have bolted but before they produce viable seed. When using manual removal techniques it is important to minimize soil disturbance around removed plants since it can create an ideal site for re-establishment by new seedlings or invasion by another undesirable species.
Competition: Cultural control of yellow starthistle includes revegetation programs in which infested sites are seeded with either native or high forage non-native perennial grasses. Revegetation with desirable and competitive plant species is an important part of most integrated management strategies, and can be the best long-term sustainable method of suppressing yellow starthistle invasions, establishment, or dominance while providing high forage production.
Fertility: A vigorous community of desirable vegetation uses soil moisture and shades the soil surface, impeding establishment of yellow starthistle. Any activity that disturbs the soil and/or increases sunlight at the soil surface can encourage yellow starthistle.
Cultivation: Any tillage operation that severs the roots below the soil surface can effectively control yellow starthistle, which probably accounts for the uncommon occurrence of yellow starthistle as a cropland weed. Tillage is sometimes used for yellow starthistle control on roadsides. Early summer tillage, before viable seeds are set, and repeated tillage following rainfall/germination events will rapidly deplete the yellow starthistle seed bank, but may also have the same effect on the seed bank of desirable species.
Mowing:

Mowing may be an effective control method for yellow starthistle in accessible areas under intensive management, along roadsides, in recreational areas, and where landowners do not wish to use herbicides. Successful control with mowing depends on proper timing, the growth form of yellow starthistle, and the availability of desirable plants to fill the emptied niche. The degree of control one can expect with mowing also varies with site conditions and available moisture after defoliation. It is therefore important to monitor and follow-up with whatever action may be indicated to achieve satisfactory control.

Mowing too early (before seedheads reach spiny stage) or too late (after seed set) will usually increase the yellow starthistle problem. Mowing too early in the season can remove associated grass (native species are negatively impacted) cover and promotes more vigorous yellow starthistle regrowth. If done too late, mowing scatters yellow starthistle seed.

Grazing: Grazing management is critical to successful management of yellow starthistle on rangelands. A detailed summary of grazing management practices to deter invasion by yellow starthistle is given by DiTomaso.
Cattle, sheep and goats will graze on yellow starthistle in early spring, and up to the bolting stage. These ruminants will not graze yellow starthistle plants after the spines emerge. Yellow starthistle provides forage for ruminants in late spring and early summer when other green forage is generally unavailable. Properly timed grazing by cows, sheep and goats can effectively manage yellow starthistle stands, but will not eliminate populations.
Yellow starthistle is toxic to horses, causing a neurological disease called equine nigropallidal encephalomalacia, or "chewing disease" with prolonged ingestion. Poisoning is most likely when yellow starthistle is the only feed available or when yellow starthistle is a substantial contaminant of dried hay. In some cases, horses acquire a taste for yellow starthistle and seek it out even when other forage is available. Other animals (e.g. mules and burros) are not susceptible to the toxic effects.
Optimum control is achieved when yellow starthistle is grazed in the bolting, pre-spiny stage, followed by 1 to 3 additional grazings to remove regrowth, as long as yellow starthistle continues to bolt. This prescription must be continued for at least 3 years in a severe infestation to reduce the yellow starthistle seed bank. Grazing at this time allows annual grasses, legumes and most other resident annuals to complete their life cycle and set seed, allowing for seed bank replenishment and leaving appreciable amounts of plant residues on the ground.
Fire: Fire usually kills yellow starthistle plants, although some plants may resprout after low severity burning. Fires are usually not severe enough to kill yellow starthistle seed.
The effectiveness of fire in killing invasive plants or reducing their population growth depends on fire severity, time of burning, and prior and subsequent weather conditions [29], as well as the species present in the preburn community and represented in the soil seed bank.
Bio-Control: No bio-control agents at this time available in Alberta.
Four (4) bio-control agents have been imported from Europe to the US for Yellow Star-thistle control.  They are weevils ( 1 Bangastemus Prientalis and 2 Eustenopus Villosus), and Flies (3 Urophora Sorunaseva and 4 Chaetorellia Succinea), which attack the flower heads; reducing seed production.
Chemical Control: Of particular concern for yellow starthistle control is its resistance to picloram and some other synthetic auxin herbicides. DiTomaso  summarizes the literature on herbicide resistance of yellow starthistle, noting that picloram resistant plants were also cross-resistant to clopyralid, dicamba and fluroxypyr, but not to triclopyr or 2,4-D, all of which are synthetic auxins and have the same mode of action as picloram (WRIC).
Other Canadian Links: Government of Canada Poisonous Plant Website
http://www.cbif.gc.ca/pls/pp/ppack.info?p_psn=58&p_type=all&p_sci=sci
British Columbia Government
http://www.weedsbc.ca/weed_desc/yel_star.html
Alberta Invasive Plant Council
http://www.invasiveplants.ab.ca/Downloads/FS-YellowStarthistle.pdf
Invasive Species Council of Manitoba
http://www.invasivespeciesmanitoba.com/site/uploads/pdf/Yellow%20Starthistle%20(Read-Only).pdf
Herbarium Collections: 1. University of Alberta Vascular Plant Herbarium -  1 specimen from 1981, collector George Moreland from Pibroch, AB
Life Cycle: Yellow starthistle in an invasive winter annual, or rarely a biennial or short-lived perennial forb.


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Last Modified: 2012-01-06 11:01:27.865

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