Source: California Invasive Plant Council
URL of this page: http://www.cal-ipc.org/ip/management/ipcw/pages/detailreport.cfm@usernumber=26&surveynumber=182.php
Invasive Plants of California's Wildland
|Scientific name||Centaurea calcitrapa|
|Additional name information:||L.|
|Common name||purple starthistle, red star thistle, red starthistle, St. Barnaby’s thistle, golden starthistle|
|Synonymous scientific names||none known|
|Closely related California natives||0|
|Closely related California non-natives:||11|
|Listed||CalEPPC List B,CDFA B|
|By:||John M. Randall|
HOW DO I RECOGNIZE IT?
starthistle (Centaurea calcitrapa) is an annual to perennial thistle with
a mounding growth habit and heads of purple flowers surrounded by long, stout,
sharp-pointed spines. Plants form rosettes in their first growing season, the
leaves deeply pinnately lobed and gray-hairy with light-colored midribs; older
rosettes have a circle of spines in the center. Mature plants are one to four
feet high, densely and rigidly branched, and have numerous flowerheads (Roche
and Roche 1990). Purple starthistle is similar to Iberian starthistle
(Centaurea iberica), which is also found in
Mature plants 0.5 to 4 ft (20-130 cm) tall, often more or less mounded and densely and rigidly branched. Lower leaves on bolted plants are 4-8 in (10-20 cm) long and more or less deeply lobed. Flower heads many, each surrounded by leaves, involucres 0.25-0.3 in (6-8 mm) in diameter, 0.6-0.8 in (1.5-2 cm) long, ovoid in outline, main phyllaries greenish or straw-colored and tipped with a stout spine 0.4-1 in (1-2.5 cm) long, spine with a fringe of small spines at base. There are 25-40 flowers in each flowerhead. Corollas 0.6-1 in (1.5-2.5 cm) long, purple. Flowers at margins of flowerheads not enlarged as in some species of Centaurea. Achenes about 1/8 in (2.5-3.5 mm) long, white or brown streaked, smooth, with no pappus. The species epithet calcitrapa is derived from the word caltrop, a weapon with protruding spikes used in ancient times to obstruct the movement of cavalry. (Description from Hickman 1993, Roche and Roche 1990, Tutin et al. 1976)
|WHERE WOULD I FIND IT?||
Purple starthistle is
most troublesome in recently or repeatedly disturbed areas such as pastures and
overgrazed rangelands and along roads, ditches,
and fences, usually below 3,000 feet (1000 m) elevation. It is most prolific on
fertile soils and seems to prefer heavier bottomland and clay soils (Roche and
Roche 1990). Found along the coast from
|WHERE DID IT COME FROM AND HOW IS IT SPREAD?||
starthistle is native to the Mediterranean region of southern
|WHAT PROBLEMS DOES IT CAUSE?||
Purple starthistle is a pest of pastures, and in the San Francisco Bay Area it is regarded as a major problem (Roche and Roche 1990). It has also invaded some grassland preserves, notably within the East Bay Regional Park District and at the Jepson Prairie Preserve northwest of Rio Vista. It is not clear whether purple starthistle can form dense infestations in grasslands not subject to heavy grazing or other disturbances, but it is suspected that it can and that it will replace desirable native species.
Purple starthistle’s stiff, sharp spines and bitter taste discourage feeding by cattle, deer, and rodents (Amme 1985). It replaces palatable species in some grazed areas, and dense stands of mature plants can make areas inaccessible to livestock and humans (Roche and Roche 1990). Its spines are thicker and stronger than those of yellow starthistle and do not fall from the plants in autumn as do those of yellow starthistle. Because of this, forage that may grow in infested areas during fall and winter after purple starthistle has senesced may be inaccessible to grazers.
|HOW DOES IT GROW AND REPRODUCE?||
|HOW CAN I GET RID OF IT?|
methods: Grubbing or digging can control small infestations. Amme (1985)
reported that purple starthistle populations were sharply reduced after three
years of hand grubbing efforts at the Las Trampas site in the
Mechanical methods: Mowing is not an effective method of control. The rosettes are too low to be cut and plants that have already bolted often respond to mowing by producing multiple rosettes. Mowing plants that have begun to flower will spread the cut flowerheads, which may still be capable of dropping mature seed.
Insects and fungi: There is no biological control program for purple starthistle. Two species of Bangasternus seed head weevils that have been introduced to control yellow starthistle (Centurea. solstitialis) are reported to have ‘biotypes’ that feed on purple starthistle in Europe but there are no plans to introduce these to North America.
Grazing: Conventional grazing by sheep or cattle will not control purple starthistle and in fact can promote it, because grazing animals usually avoid this plant and selectively feed on species that would otherwise compete with it. It has been suggested, however, that rotational grazing practices with short graze periods followed by recovery periods may reduce purple starthistle and promote grasses and other species that compete with it (DiTomaso pers.comm.).
Clopyralid, 2,4-D and dicamba provided effective control of purple starthistle but had little or no effect on grasses (Whitson et al. 1987). Late winter or spring application is recommended because the seedlings and rosettes are most sensitive at this time (Roche and Roche 1981). Amme (1985) reported that a 1 percent solution of glyphosate killed all purple starthistle along a rocky road shoulder.