Weed of the Week 

Produced by the USDA Forest Service, Forest Health Staff, Newtown Square, PA. WOW 03-10-06

Invasive Plants website: http://www.na.fs.fed.us/fhp/invasive_plants 

Yellow Starthistle

Centaurea solstitialis L. 

Native Origin: Europe- Mediterranean 

region

Description: An annual herbaceous plant 

in the aster family (Asteraceae) growing 

from 1.5-3 feet in height. Plants are graygreen to blue-green and have deep 

taproots. Stems and leaves are covered 

with cottony wool. Basal leaves are 2 to 3 

inches long and deeply lobed. Upper 

leaves are short and narrow, with few 

lobes. Flowers are bright yellow with 

tubular florets and sharp spines 

surrounding the base. Spread of yellow 

starthistle is by seed and each seed head can produce from 35 to 80 or more seeds. Most seeds move no 

more than two feet from the parent plant without assistance of animals (wildlife, livestock, and humans). 

Habitat: Plants typically thrive in full sunlight and deep, well-drained 

soils, where annual rainfall is between 10-60 inches, and is especially 

common in disturbed areas, roadsides and rangelands. 

Distribution: This species is reported from states shaded on Plants 

Database map. It is reported invasive in CA, ID, OR, NJ, UT, and WA. 

Ecological Impacts: It chokes out the native plants, reducing 

biodiversity, and wildlife habitat and forage. It is legally controlled in 

some states where it is replacing important forage vegetation and 

reducing rangeland values. 

Control and Management: 

• Manual- Plants can be pulled, hoed, tilled or mowed before bloom. Controlled burns are successful if 

repeated for 3 consecutive years. 

• Chemical- It can be effectively controlled using any of several readily available general use herbicides such 

as glyphosate, triclopyr, clopyralid or picloram between December and April seems to be the most effective. 

Application during the winter encourages the growth of other, more desirable, plants. Follow label and state 

requirements. 

• Biological Control: Six biological control insects have been released in the United States for yellow 

starthistle control: Bangasternus orientalis, Eustenopus villosus, Urophora jaculata, Urophora sirunaseva, 

Larinus curtus, and Chaetorellia australis. Of these, five became established and three (B. orientalis, U. 

sirunaseva and E. villosus) are widespread. Also, the accidentally introduced fly, Chaetorellia succinea has a 

strong affinity to yellow starthistle and is found almost everywhere yellow starthistle occurs. All of these 

insects attack the seed head of yellow starthistle, effectively limiting the number of seeds the plants are 

able to produce. Current research indicates that the insects have reduced seed yield by at least 50%. The 

rust fungus, Puccinia juncea var. solstitialis was released in California in 2003. It is too early to know if this 

rust will establish and eventually cause high mortality of yellow starthistle in the wild. Several more fungi 

and insects are currently being tested for introduction into the United States. 

• Grazing: Sheep, goats, and cattle graze on yellow starthistle in early spring, before the flower’s spines 

develop. Goats also graze plants in the spiny or flowering stages. Grazing reduces biomass and seed 

production. 

References: www.forestimages.org, http://plants.usda.gov, www.nps.gov/plants/alien, 

Czarapata, Elizabeth J. Invasive Plants of the Upper Midwest, An Illustrated Guide to their Identification and 

Control, 2005 p. 134, www.invasive.org