yellow star-thistle (Centaurea solstitialis) Plant Guide

Plant Guide

YELLOW STAR-

THISTLE

Centaurea solstitialis L.

Plant Symbol = CESO3

Contributed by: USDA NRCS Montana/Wyoming

Plant Materials Program

Figure 1. Yellow star-thistle flower heads. Photo by

Mark Stannard, USDA-NRCS Pullman Plant Materials

Center, Pullman, Washington.

Alternate Names

Yellow starthistle

Uses

Flowers provide nectar for honey bees.

Status

Yellow star-thistle is a listed noxious weed and is

invasive in many western states. Consult the

PLANTS Web site and your State Department of

Natural Resources for this plant’s current status (e.g.,

threatened or endangered species, state noxious

status, and wetland indicator values).

Weediness

Yellow star-thistle is one of the more invasive weeds

of the Intermountain West and Pacific Northwest. A

report from 2003 estimated that yellow star-thistle

has infested nearly 15 million acres in 17 western

states. This plant is weedy and invasive in some

regions or habitats and often displaces desirable

vegetation if not properly managed. Consult with

your local NRCS Field Office, Cooperative

Extension Service office, state natural resource, or

state agriculture department regarding its status and

use. Weed information is also available from the

PLANTS Web site at

http://plants.usda.gov/. Also

consult related web sites listed in PLANTS for this

species for further information.

Description

General: The rosette of yellow star-thistle lies close

to the ground (see Figure 2) and produces six to 28

deeply lobed leaves that range from one to eight

inches (2.5 to 20 centimeters) long and are generally

less than two inches (5 centimeters) wide. The rigidly

branched, winged flowering stems (see Figure 2)

average about two feet (60 centimeters) tall, but

range from four inches (10 centimeters) to five feet

(1.5 meters), depending on environmental conditions.

The stem leaves are entire without lobes, linear in

shape, and are vested with woolly hairs that persist

through the growing season. Flower heads are

solitary on the ends of short stems and have many

bright yellow flowers (see Figure1). The bracts of the

flower heads are armed with stout, straw-colored

spines one to two inches (2.5 to 5 centimeters) long

that radiate from the flower head in a star shape.

Figure 2. A yellow star-thistle rosette and flowering

stem showing leaf shapes and the winged stem. Photo by

Jane Mangold, Montana State University, Bozeman,

Montana.

Distribution: Yellow star-thistle is native to the

Mediterranean region. It has been reported in most

states in the United States and in four Canadian

Provinces. For current distribution, consult the Plant

Profile page for this species on the PLANTS Web

site.

Habitat: Yellow star-thistle prefers deep loamy soils

with south facing slopes and 12 to 25 inches or more

of annual rainfall with a bimodal distribution in the

fall and spring. It favors perennial bunchgrass

communities dominated by bluebunch wheatgrass,

Idaho fescue, and Sandberg’s bluegrass. Although it

does not compete well with sagebrush, it readily

invades sagebrush communities after disturbance. It

is most common in disturbed areas in full sun, such

as rangelands, along highways or roads, railroad

tracks and other transportation or communication

lines. In Montana small patches have occurred along

road sides, in new alfalfa seedings (from

contaminated seed) and other disturbed areas such as

construction lots. Because patches were controlled

before they could establish and spread, it is unknown

if certain regions or plant community types in

Montana are more vulnerable. In Idaho large areas of

canyon grasslands, rangelands, pasture, roadsides and

other disturbed areas primarily in western to northern

regions are infest with yellow star-thistle. Research in

west central Idaho found rangelands with south to

southwest aspects and 20-30% plus slopes were most

vulnerable to yellow star-thistle invasion. In eastern

Oregon it is common in grassland foothills. In

Washington it is common on south-facing grassland

slopes, primarily in the south eastern part of the state.

In California it is prevalent in the Central Valley and

surrounding foothills and continues into mountainous

regions below 7,000 feet (2,100 meters).

Adaptation

In its native range, yellow star-thistle evolved under

Mediterranean climatic conditions characterized by

precipitation in the fall and spring, and dry conditions

in the winter and summer.

Establishment

Yellow star-thistle is a winter annual dependent on

seed production for population growth and spread.

Plants normally produce 20 to 120 seeds each, but

under ideal conditions production may exceed

100,000 seeds per plant. Up to 90 percent of the

seeds have a short plume (pappus). These seeds

disperse at maturity and readily germinate when

moisture is available in the fall. The other 10 percent

lack a plume, disperse over winter, and may remain

dormant in the soil for two to three years. One-

quarter to one-half inch (0.6 to 1.3 centimeters) of

rain in the fall is sufficient to stimulate germination

and seedling emergence. Seedling densities in have

been reported as high as 2,500 per square foot.

Populations overwinter as seedlings or rosettes. Seed

can also germinate in the spring.

Beginning in March and continuing through May,

seedlings transition into rosettes. Normally, between

60 and 75 percent of the rosettes die from self-

thinning and moisture stress. Surviving rosettes

produce a tap root capable of penetrating deeply into

the soil to access deep soil moisture. A flower stalk

grows from surviving rosettes and blooms in mid-

summer. Flowers are primarily pollinated by

honeybees (Apis spp.) and bumblebees (Bombus

spp.), and germinable seed is produced eight days

after flower initiation. Spring emerging seedlings are

capable of blooming in the year of emergence or

overwintering to bloom in the following year.

Management

See Control below

Pests and Potential Problems

See the biological control section under Control

below.

Environmental Concerns

Yellow star-thistle is problematic on canyon lands,

rangelands, pastures, roadsides, and disturbed areas.

Its rapid growth rate and aggressive resource

acquisition make it competitive in native plant

communities where it forms dense stands displacing

native species and reducing diversity. Loss of native

bunchgrasses reduces available forage for livestock

and wildlife, and the long, stout spines on the flowers

deter grazing. Consumption of yellow star-thistle by

horses causes chewing disease, a fatal nervous

disorder. Rosettes can be grazed by cattle and sheep

before the spiny flower heads form.

Control

Contact your local agricultural Extension specialist or

county weed specialist to learn what works best in

your area and how to use it safely. Always read label

and safety instructions for each control method.

Trade names and control measures appear in this

document only to provide specific information.

USDA NRCS does not guarantee or warranty the

products and control methods named, and other

products may be equally effective.

Herbicide: There are many herbicides effective for

controlling yellow star-thistle including glyphosate,

2,4-D, picloram, dicamba, clopyralid and others. For

optimal population regulation, herbicide should be

applied at the transitional stage from rosettes to

flowers and before the population has advanced

beyond the 2% flower initiation stage.

Biological: Five insect species have been released in

the western United States for the management and

control of yellow star-thistle. They feed on the flower

buds and seedheads and can reduce seed production

from 45 to 100 percent. There is also a rust fungus

that reduces the vigor of yellow star-thistle plants.

Burning: Prescribed fire has been effective in

reducing populations. Burns conducted for three

consecutive years in late June and early July after the

dispersal of desirable grass seed but before yellow

star-thistle seed production, reduced the yellow star-

thistle seed bank, seedling density, and summer

vegetative cover each by over 90 percent.

Hand pulling: Hand pulling that removes the root

crown is effective for new, small introductions of

yellow star-thistle. To prevent seed dispersal,

flowering plants should be destroyed in a hot fire or

bagged and disposed of in an appropriate landfill.

Repeated monitoring should be planned for every two

to four weeks during the growing season.

Mowing: Where the plant is dense and widespread,

timely mowing over a three-year period has reduced

plant density. Mowing may reduce seed production,

but it does not eliminate it, and may serve to spread

seed. When mowing is followed by rain, seed

production may increase. Always clean mowing

machinery before moving to weed-free areas.

Tillage: Tillage will control yellow star-thistle in

annual cropping systems. On disturbed sites

vulnerable to weed invasion, tillage should be

considered as a seedbed preparation prior to

revegetation. Quickly establishing competitive,

desired vegetation following disturbance may

decrease the chance for invasive weeds like yellow

star-thistle to become established.

Seed and Plant Production Not applicable

Cultivars, Improved, and Selected Materials (and

area of origin) Not applicable

References

Benwefield, C.B., J.M. DiTomaso, and G.B. Kyser.

2001. Reproductive biology of yellow star-

thistle: maximizing late-season control. Weed

Science 49:83-90.

DiTomaso, J.M. 2005. Yellow star-thistle (Centaurea

solstitialis L.).

DiTomaso, J.M., M.S. Hastings, and G.B. Kyser.

1999. Prescribed burning for control of yellow

star-thistle (Centaurea solstitialis) and enhanced

native plant diversity. Weed Science 47:233-242.

: C.L. Duncan and J.K. Clark

(eds), Invasive plants of range and wildlands and

their environmental, economic, and societal

impacts. Weed Science Society of America,

Lawrence, KS. Pages 36-50.

Pitcairn, M.J., G.L. Piper, and E.M. Coombs. 2004.

Yellow Star-thistle.

Sheley, R.L. and L.L. Larson. 1997. Cheatgrass and

yellow star-thistle growth at 3 soil depths.

Journal of Range Management 50: 146-150.

: Coombs, E.M., Coombs,

J.K. Clark, G.L. Piper, and A.F. Cofrancesco, Jr.

(eds), Biological control of invasive plants in the

United States. Oregon State University Press,

Corvallis, OR. Pages 233-262.

Sheley, R.L., L.L. Larson, and J.S. Jacobs. 1999.

Yellow Star-thistle.

Prepared By: Jim Jacobs, Plant Materials Specialist,

USDA NRCS Montana State Office, Bozeman,

Montana

: Sheley, R.L. and J.K.

Petroff (eds), Biology and Management of

Noxious Rangeland Weeds. Oregon State Press,

Corvallis, OR. Pages 408-416.

Jane Mangold, Extension Invasive Plant Specialist,

Montana State University, Bozeman, Montana

Hilary Parkinson, Research Associate, Montana State

University, Bozeman, Montana

Melissa Medley, Extension Weeds Integrated Pest

Management Specialist, Montana State University,

Bozeman, Montana

Dan Ogle, Plant Materials Specialist, USDA NRCS,

Boise, Idaho

Citation

Jacobs, J., J. Mangold, H. Parkinson, and M. Graves.

2011. Plant Guide for Yellow Star-thistle (Centaurea

solstitialis). USDA-Natural Resources Conservation

Service, Montana State Office. Mozeman, Montana

59715.

Published September 2011

Edited: 18July2011 jsj; 1Aug2011 mm, 3Aug2011

jm; 8Aug2011 hp; 25Aug2011 dgo

For more information about this and other plants,

please contact your local NRCS field office or

Conservation District at

http://www.nrcs.usda.gov/

and visit the PLANTS Web site at

http://plants.usda.gov/ or the Plant Materials Program

Web site

http://plant-materials.nrcs.usda.gov.

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availability of other Web sites.

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