NRCS−Montana−Technical Note−Invasive Species−MT-32 1 

United States Department of Agriculture

NATURAL RESOURCES CONSERVATION SERVICE

Invasive Species Technical Note No. MT-32

April 2011

Ecology and Management of Yellow Starthistle (Centaurea solstitialis L.)

By

Jim Jacobs, Plant Materials Specialist, NRCS, Bozeman, MT 

Jane Mangold, Extension Invasive Plant Specialist, Montana State University, Bozeman, MT 

Hilary Parkinson, Research Associate, Montana State University, Bozeman, MT 

Melissa Graves, Extension Weeds Integrated Pest Management Specialist,

Montana State University, Bozeman, MT 

Figure 1. Yellow starthistle growing along Interstate 90 in Gallatin County, Montana. Photo by Mike 

Jones, Gallatin County Weed District. 

Abstract

Yellow starthistle is one of the more invasive weeds of the Pacific Northwest. A report from 2003 

estimated that yellow starthistle infested nearly 15 million acres in 17 western states, with the 

majority of acres (12 million) being in California. In Montana it is currently the only Priority 1A 

listed noxious weed, meaning established populations are not in the state, and management criteria 

include education, prevention, and eradication when populations are found. Since 1958, 18 

populations have been reported and controlled in Montana. 

Native to the Mediterranean region of Europe, yellow starthistle is a winter annual in the Asteraceae 

family. Seeds germinate in the fall and plants overwinter as seedlings. Seedlings transition into 

rosettes in early spring. Plants bolt and form spiny flowers (see Figure 1) in summer and may 

continue flowering until frost. Seeds set and disperse in late summer and early fall. Populations of 

yellow starthistle form dense stands on rangelands, pastures, roadsides, and wastelands where they 

displace plant native communities affecting critical wildlife habitat, accelerate soil erosion, and 
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reduce forage for livestock and wildlife. Yellow starthistle causes chewing disease in horses which 

is typically fatal. 

Prevention, early detection and rapid response to eradicate new populations are the management 

priorities for Montana. New populations should be reported to county Extension agents or weed 

coordinators. Control options will include hand pulling to remove plants with seeds and herbicide 

applications. Consult your county Extension agent or weed coordinator for the best herbicide 

options for your area. 

Figure 2. A yellow starthistle plant showing the lobed rosette leaves and winged stem. Photo by Jane 

Mangold, Montana State University, Bozeman, Montana. 

PLANT BIOLOGY

Identification

The rosette of yellow starthistle (see Figure 2) lies close to the ground and produces six to 28 deeply 

lobed leaves that range from one to eight inches long (2.5 to 20 centimeters) and are generally less 

than two inches wide (5 centimeters). 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. 

Flowerheads are single on the ends of short stems and have many bright yellow flowers. The bracts 

of the flowerheads are armed with stout, straw-colored spines one to two inches long (2.5 to 5 

centimeters) that radiate from the flowerhead in a star shape (see Figure 3). 
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Figure 3. A yellow starthistle flower. Photo by Brother Alfred Brousseau at USDA, NRCS, PLANTS 

Database. 

Life History

Yellow starthistle 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% 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 can remain dormant in the soil for up to 10 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 Washington have been reported as high 

as 2,500 per square foot. Populations overwinter as seedlings or rosettes. Seedlings can also 

germinate in the spring.

Beginning in March and continuing through May, seedlings transition into rosettes. Normally, 

between 60% and 75% 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.

Spread

More than 90% of yellow starthistle the seeds fall within two feet of the parent plant. The pappus 

plumes present on 75-90% of the seeds are too short to catch wind and are believed instead to help 

orient the seed on the soil for germination and establishment. This results in populations with slow 

invasion fronts. Birds including finches, quail, and pheasants feed on yellow starthistle seeds and 

disperse them short and long distances. Other animals, people and vehicles may also transport 

seeds long distances. Pappus bristles are covered with stiff microscopic barbs that readily adhere to 

hair and clothing where they can be spread long distances by the movement of animals and people. 

The original seed source for North American invasion is believed to be from contaminated alfalfa 

seed.
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Habitat 

In its native range, yellow starthistle evolved under Mediterranean climatic conditions characterized 

by precipitation in the fall and spring, and dry conditions in the winter and summer. Similar 

climatic conditions are found in the North American steppe region where it is invasive on most 

rangelands. It prefers deep loamy soils with south facing slopes and 12 to 25 inches 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 California it is prevalent in the Central Valley and surrounding foothills and 

continues into mountainous regions below 7,000 feet (2,100 meters). In southwestern Oregon it is 

common in grassland foothills. In Washington it is most common on south-facing grassland slopes, 

primarily in the southeastern part of the state. Research in central Idaho found rangelands with 

south to southwest aspects and 20-30% slopes were most vulnerable to yellow starthistle invasion. 

Impacts

Yellow starthistle is problematic on rangelands, pastures, roadsides, and waste areas. Its rapid 

growth rate and aggressive resource acquisition make it competitive within 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 starthistle by horses causes chewing disease, a 

fatal nervous disorder. Rosettes can be grazed by cattle and sheep before the spinney flower heads 

form. Flowers provide nectar for honeybees. 

MANAGEMENT

Prevention

Currently there are no known viable populations of yellow starthistle in Montana, and 

therefore prevention is critical. Over the last 10 years, two infestations were found in newly 

seeded alfalfa fields, suggesting the introductions were from contaminated seed. Two infestations 

were also reported from disturbed sites and believed to be introduced from seed carried on heavy 

equipment. An infestation was reported from a chain-up area along the interstate, suggesting 

vehicular transport. Most of these recent introductions were one or two plants that were removed 

before seeds were produced emphasizing the importance in early detection and rapid response. 

These occurrences are reminders to use certified weed-free seed and hay, to scout newly seeded hay 

ground and pasture, to survey constructions sites and corridors of transport, and to report suspected 

populations to county weed coordinators or Extension agents. 

Hand pulling

Hand pulling that removes the root crown is effective management for new, small introductions of 

yellow starthistle. To prevent seed dispersal, flowering plants should be destroyed in a hot fire or 
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bagged and disposed of in an appropriate landfill. Repeated monitoring should be planned for every 

two to four weeks during the growing season. 

Herbicide

There are many herbicides effective for controlling yellow starthistle including glyphosate, 2,4-D, 

picloram, dicamba, clopyralid and others. Consult with your county Extension agent or weed 

coordinator for the herbicide treatment that works best in your area and always follow label 

instructions for the optimal control and minimal environmental risk. 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.

Mowing

In parts of California where the plant is dense and widespread, timely mowing over a three-year 

period has reduced plant density. However, this is not an effective strategy in Montana where 

populations are small and eradication, not suppression, is the management goal. Mowing may 

reduce seed production, but it does not eliminate it, and may serve to spread seeds. When mowing 

is followed by rain, seed production may increase. 

Tillage

Tillage is not a viable method of yellow starthistle control in Montana. However, for 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 starthistle to become established (see 

revegetation below). 

Burning

Prescribed fire has been effective in reducing populations in California. Burns conducted for three 

consecutive years in late June and early July after the dispersal of desirable grass seed but before 

yellow starthistle seed production, reduced the yellow starthistle seed bank, seedling density, and 

summer vegetative cover each by over 90%. However, in Montana burning is not an appropriate 

management strategy to eradicate newly established, small populations.

Biological 

Because there are currently no known naturalized populations of yellow starthistle in Montana, 

biological control insects are not a practical control option in this state. Five insect species have 

been released in the western United States for the management of yellow starthistle. They feed on 

the flower buds and seedheads and can reduce seed production from 45% to 100%. There is also a 

rust fungus that reduces the vigor of yellow starthistle plants.

Revegetation 

Because there are no large-scale yellow starthistle populations in Montana, revegetation is not a 

practical option for control. However, due to the fact that two recent introductions are associated 

with heavy equipment disturbance, restoring perennial vegetation after such disturbances is a 

priority. Competitive plants will reduce seedling survival; slow population spread, and makes 
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eradication more probable where yellow starthistle seeds are unintentionally introduced on 

disturbed sites. Also, where hay meadows and pastures are revegetated as part of a crop rotation or 

newly established field, scouting for new introductions is important for early detection in the event 

the crop seed was contaminated with yellow starthistle seed.

Integrated Pest Management (IPM)

The most important part of IPM for yellow starthistle in Montana is prevention and early detection 

followed by rapid response. This is facilitated by an educated and aware public, particularly people 

who work in the field that can identify and report introductions during the early phase of invasion. 

New populations should be reported to the county Extension agent, county weed coordinator, or 

Montana Department of Agriculture (406) 444-3140, so steps can be taken to prevent population 

spread. The most practical combination of controls is hand pulling to remove plants with seed and 

herbicide application to kill seedlings and rosettes. Scouting and surveys should be concentrated on 

newly seeded hay meadows and pastures and on sites of heavy equipment disturbances such as 

utility construction sites. Highways should be regularly surveyed to detect new populations 

established from seed transported on vehicles. 

References

Benwefield, C.B., J.M. DiTomaso, and G.B. Kyser. 2001. Reproductive biology of yellow 

starthistle: maximizing late-season control. Weed Science 49:83-90. 

DiTomaso, J.M. 2005. Yellow starthistle (Centaurea solstitialis L.). In:

DiTomaso, J.M., M.S. Hastings, and G.B. Kyser. 1999. Prescribed burning for control of yellow 

starthistle (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 Starthistle. In: 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. and L.L. Larson. 1997. Cheatgrass and yellow starthistle growth at 3 soil depths. 

Journal of Range Management 50: 146-150. 

Sheley, R.L., L.L. Larson, and J.S. Jacobs. 1999. Yellow Starthistle. In: Sheley, R.L. and J.K. 

Petroff (eds), Biology and Management of Noxious Rangeland Weeds. Oregon State Press, 

Corvallis, OR. Pages 408-416.