Yellow starthistle (Centaurea solstitialis)

Yellow starthistle has long spines on its yellow flowers

 
 

Yellow starthistle is an annual plant with long, sharp spines below its yellow flowers. It is a major issue in rangelands in the western United States as it displaces native species and its spines injure grazing animals. It is not documented to be present in Minnesota, so any potential sightings should be reported to the Minnesota Department of Agriculture.

Caution: Plants have sharp spines on their flower heads. Yellow starthistle is toxic to horses, mules, and burros.

Description

Appearance

Yellow starthistle is an annual plant (sometime biennial) that starts as a rosette of leaves close to the ground and then puts up flowering stalks that can reach up to 6 feet tall, but are usually 1-3 feet tall.

Leaves and Stem

In the fall, seeds germinate and the plant forms a circular clump of leaves (rosette) close to the ground. These rosette leaves have deep lobes and are 2-6 inches long. The next spring and summer, the plant sends up multiple flowering stalks that can grow up to six feet tall, but are usually 1-3 feet tall. Leaves on the stem are alternate (come off the stem one at time at each leaf node). Leaves on the stem are linear (long and narrow), not lobed, and have smooth edges. The stems have linear green ribbon-like "wings" along the stem. Stems and leaves have woolly, white-gray hairs.

Flowers

Clusters of tiny yellow flowers make up the yellow starthistle flower heads. Below the yellow flowers are green leaf-like bracts. Long spines extend from these bracts. The spines are ¾ inch long, sharp, and give the star-shaped look that gives yellow starthistle its name.

Seeds

Yellow starthistle has small seeds and the majority of seeds have feathery, white tufts attached to them to aid in wind dispersal, while the rest of the seeds do not have the white tufts.

Roots

Yellow starthistle has a deep taproot.

Biology

Yellow starthistle is considered a winter annual because it generally germinates in the fall, forms a rosette of leaves, overwinters as the rosette, sends up a flowering stalk the next spring, flowers and then dies. Yellow starthistle generally grows in sunny areas and can grow in a variety of soil moisture conditions from wet to dry. Yellow starthistle is typically found in grasslands, pastures, natural areas, and disturbed areas.

Origin and Spread

Yellow starthistle is native to Europe. It was likely accidently introduced to North America in contaminated alfalfa seed. It has since spread to much of the western United States and has a more limited distribution in the eastern United States. Yellow starthistle is not known to be present in Minnesota, but has been reported in North Dakota, South Dakota, Iowa, and Wisconsin.

Refer to EDDMapS Distribution Maps for current distribution.

Don't be fooled by these look-alikes

  • Spotted knapweed, Centaurea stoebe spp. micranthos (invasive), diffuse knapweed, Centaurea diffusa (invasive), meadow knapweed, Centaurea x moncktonii (invasive), and brown knapweed, Centaurea jacea (invasive) – These knapweeds have pink or white flowers, unlike the yellow flowers of yellow starthistle and they lack the one inch long spines on their flowering heads that yellow starthistle has. View the "Meet the Knapweeds" brochure for a side-by-side comparison of spotted, diffuse, meadow, and brown knapweeds.
  • Canada thistle, Cirsium arvense (invasive) – Canada thistle has pink flowers with smooth green bracts below them, unlike yellow starthistle which has yellow flowers with long spines below the flowers. Canada thistle leaves are deeply lobed and have spines along the edges while yellow starthistle leaves along the stem are linear and do not have spines.
  • Autumn sneezeweed, Helenium autumnale (native) – has yellow flowers and winged stems, but leaves are somewhat diamond shaped and have toothed edges, while yellow starthistle leaves along the stem are linear and have smooth edges.
  • Common mullein, Verbascum thapsus (invasive) – has yellow flowers, winged stems, and fuzzy leaves, but the flowers grow in an upright spike of flowers and have no spines and the leaves are large (up to 15 inches long and 5 inches wide).
 
Regulatory Classification

Yellow starthistle is a Minnesota Department of Agriculture Prohibited Noxious Weed on the Eradicate List meaning that the above and below ground parts of the plant must be destroyed. Additionally no transportation, propagation, or sale is allowed. It is not documented to be present in Minnesota, so any potential sightings should be reported to the Minnesota Department of Agriculture

Threat to Minnesota
  • Yellow starthistle forms large, dense monocultures that displace native species and habitat and overtake grasslands, pastures, natural areas, and disturbed areas.
  • Its spines injure grazing animals and it is toxic to horses, mules, and burros. This has a negative economic impact for people who raise grazing animals and decreases land values.
What you should do

One way that invasive plant seeds and fragments can spread is in soil. Sometimes plants are planted purposefully. You can prevent the spread of invasive plants.

PlayCleanGo: Stop Invasive Species in Your Tracks

  • REMOVE plants, animals & mud from boots, gear, pets & vehicle.
  • CLEAN your gear before entering & leaving the recreation site.
  • STAY on designated roads & trails.
  • PLANT non-invasive species.
Native Substitutes
 
Control Methods

Mechanical control can be done by repeated hand pulling or using a tool such as shovel. Use caution and protective equipment when pulling to avoid the sharp spines. Take care to remove as much of the root as possible. If pulling plants, leave plants on-site to decompose or follow Minnesota Department of Agriculture guidance for plant disposal. Yellow starthistle is a Minnesota Department of Agriculture Prohibited Noxious Weed on the Eradicate List meaning that the above and below ground parts of the plant must be destroyed, so control methods that do not kill the plant, such as mowing, are not appropriate when they are the only method used. Mowing in May through July may prevent or reduce flowering, but follow up with other treatments is necessary. Do not mow when seed is present (generally August through November) as this can spread the seed.

Herbicide control can be done using systemic herbicides which are taken up by plants and move within the plant, which can kill leaves, stems, and roots. Herbicide formulations including aminopyralid, clopyralid, and picloram have been found to provide good control. April, May, and June are the most effective months for herbicide application. Contact the Minnesota Department of Agriculture Noxious Weed Program for advice on managing yellow starthistle.

Reporting

Report new occurrences by submitting a report through EDDMapS Midwest, emailing Arrest The Pest, calling Arrest the Pest (1-888-545-6684), or contacting your local county agricultural inspector. Yellow starthistle is not documented to be present in Minnesota, so any potential sightings should be reported to the Minnesota Department of Agriculture.

Resources