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Yellow Starthistle

Centaurea solstitialis
Updated Sep 12, 2023
 
1

Make a Positive Identification

  • Yellow starthistle lives for one growing season (annual). Seeds germinate fall through spring.
  • Following germination, plants grow a large taproot. Then they grow spreading stems from 6 inches to 5 feet tall.
  • Yellow starthistle forms yellow flowers with sharp spines at the base.
Species: Yellow Starthistle
Yellow starthistle plants growing in dense stand

"St Barnabys Thistle" by John Tann is licensed under CC BY 2.0.

Yellow starthistle grows in dense stands from 6 inches to 5 feet tall.

Species: Yellow Starthistle
Gray-green yellow star thistle stems

Steve Dewey, Utah State University, Bugwood.org

Its stems are gray-green. The extended leaf bases make the stems appear winged.

Species: Yellow starthistle
Yellow starthistle flower and spines

"St Barnabys Thistle" by John Tann is licensed under CC BY 2.0.

Yellow starthistle flowers are bright yellow with long, sharp spines at the base.

Species: Yellow starthistle
Yellow starthistle rosette

Cindy Roche, Bugwood.org

Yellow starthistle forms a rosette after germinating. Plants in this stage grow a large taproot.

Species: Yellow starthistle
Yellow starthistle seeds

Cindy Roche, Bugwood.org

Yellow starthistle plants can produce thousands of seeds. Up to 95% of seeds are viable. Seeds remain viable in the soil for 3 or more years.

LOOK-ALIKE: PURPLE AND IBERIAN STARTHISTLE
Species: Purple Starthistle
Purple starthistle stems, spines, and flower

Barry Rice, sarracenia.com, Bugwood.org

Both yellow and purple starthistle (Centaurea calcitrapa) have gray-green leaves and stems. The stems of both plants look winged. The plants look different when they flower. Purple and Iberian starthistle (another similar species) have purple flowers as shown in the photo.


Take action

Control methods for purple starthistles are similar to solutions for yellow starthistle.

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2

Yellow Starthistle Benefits

  • Yellow starthistle flowers attract pollinators, including honey bees.
 

Yellow Starthistle Risks

  • Yellow starthistle spreads quickly. It is difficult to control.
  • It displaces desired vegetation and degrades wildlife habitat and livestock forage. It is toxic to horses.
  • Yellow starthistle will dominate an area if not controlled.
  • Its spiny flowers limit human activity.
Risk Card
Does it cause harm?
Adults & Children
Some
Property
High
Pets
Some
Annoyance
High
Environment
High
Action Highly Recommended
 
3

Take Action

If you have yellow starthistle on your property, take action to control it right away.

Do I need to take action?
Yes. Remove individual plants and small patches of yellow starthistle. Both small and large patches require several years of attention to control.

What if I do nothing?
Yellow starsthistle dominates an area when left unmanaged.

 
4

Prevent Yellow Starthistle

Yellow starthistle rosette

Joseph M. DiTomaso, University of California - Davis, Bugwood.org

Look for Newly Sprouted Seedlings and Rosettes
  • Look for seedlings and rosettes.
  • Take note of their location and plan to cultivate plants as the soil dries out in the spring. Or apply herbicide as early as possible, following label directions.
  • Continue to monitor the area each year. Control it as needed.
Gloved hand using metal brush to clean shovel

Weston Miller, Oregon State University

Remove Dirt from Shoes and Equipment
  • After working or traveling in an area with yellow starthistle, clean your boots and tools. Use a wire brush to remove all soil that may contain seeds.
  • If you drive into an area with yellow starthistle, clean your vehicle. Seeds are easily transported to new locations on vehicles and equipment.
Replant Larger Areas with Technical Support
  • Yellow starthistle is difficult to expel from an infested area. Replanting a previously infested area requires planning and effort. The photo shows an area that was replanted after invasive weeds were removed.
  • Create a multi-year re-vegetation plan. Plans include site preparation, planting details, and plant care. Also follow-up control for Italian thistle and other weeds.
  • Plan for at least 2-3 years of monitoring and maintenance.
  • Contact your local Extension specialist, soil and water conservation district, or a professional re-vegetation specialist. They can suggest strategies for your area.
 
5
Solutions for Yellow Starthistle

Early Detection & Rapid Response

Watch for yellow starsthistle on property you manage. Remove it before it becomes a bigger problem.

Physically Remove Plants & Non-Chemical Options

  • Hand tools are effective to remove individual plants and small patches.
  • Cultivate yellow starthistle with a tractor-mounted disk in the spring as the soil dries out.
  • Mow yellow starthistle in the spring as the soil dries out.
  • Repeated grazing by livestock over several years weakens yellow starthistle stands. The goal is to keep it from setting seed.

Herbicides (Weed Killers)

Herbicides effectively kill yellow starthistle when used according to label directions.

Monitoring & Follow-Up

  • After treatment, return to yellow starthistle stands.
  • Look for shoots and seedlings in the spring.
  • Control it each year as needed.

NEED HELP?

Consider a licensed pest control company. Learn How to Hire a Pest Control Company.
Your local Extension Specialist in Oregon  and other states  can suggest other methods.

Jump To

Method Does it work? Is it safe? Recommendation
A
Physically Remove Stems, Chop Below Root Crown
Effective
Low risk
B
Cultivate Starthistle when Soil Dries in Spring
Effective
Low risk
C
Targeted Grazing
Somewhat effective
Low risk
D
Biological Control
Somewhat effective
Low risk
E
Herbicides Triclopyr & Glyphosate
Effective
Low risk
Use if Necessary
F
If Using Herbicides, Protect Yourself & Minimize Risks
 
A

Physically Remove Stems, Chop Below Root Crown

Non-Chemical Method

Weston Miller, Oregon State University

Physically Remove Stems, Chop Below Root Crown

Dig out individual plants and small patches.

Does it work?
Effective
  • Several years of monitoring and effort are required to get rid of yellow starthistle.
  • Use preventive measures for best results.
How much effort?
High effort
  • Cut and remove stems to access roots. Chop plants below the root crown. As annual plants, they won’t regrow.
  • Return to the area each year and take action as needed.
What's the risk?
Low risk
Possible risk of exposure or harm from chemicals
NONE
 
B

Cultivate / Mow Starthistle when Soil Dries in Spring

Non-Chemical Method

freeteo, iStock

Cultivate / Mow Starthistle when Soil Dries in Spring

Cultivate and/or mow patches of yellow starthistle to keep plants from flowering and setting seed.

 

Does it work?
Effective
  • Well-timed cultivation and/or mowing reduces seed production and weakens a population of starthistle. It requires annual treatment.
  • Use preventive measures for best results.
How much effort?
  • Mow (with a string trimmer or mower) or cultivate yellow starthistle with a tractor-mounted disk in the spring as the soil dries out.
  • It may regrow and flower after treatment. Be prepared to re-treat as needed later in the growing season.
What's the risk?
Low risk
Possible risk of exposure or harm from chemicals
NONE

Cultivating Starthistle TIPS

  • Cultivate yellow starthistle after the last rains and before flowering for best results. If you cultivate too early (before the last rains), more seeds will sprout.
  • Another cultivation will be necessary to keep remaining plants from setting seed. Managing pastures to reduce bare ground will limit starthistle establishment.

Soil Disturbance & Erosion

  • Minimize soil disturbance as much as possible when removing yellow starthistle.
  • Regrade the soil after digging out plants. Apply mulch (when appropriate).
  • Take steps to prevent erosion as needed.
  • Replant the area to shade yellow starthistle seedlings.

Mowing Starthistle

  • Carefully timed mowing limits yellow starthistle seed production.
  • Mow at the late spiny or early flowering stage.
  • Plants will regrow stems and then flowers if mowed too early.
  • You'll likely have to mow a second or third time to keep plants from flowering.
 
C

Targeted Grazing

Non-Chemical Method

Scott Bauer, USDA Agricultural Research Service, Bugwood.org

Targeted Grazing

  • Grazing animals are used by ranchers and land managers to reduce yellow starthistle growth.
  • Sheep and cattle eat starthistle before the spines on the plant form. Goats eat it at any growth stage.
  • Yellow starthistle is toxic to horses.
Does it work?
Somewhat effective
  • Grazing is a good way to knock down starthistle stems.
  • However, it will need to be repeated or followed up with other control methods.
How much effort?
High effort
  • Establish temporary fences to contain the livestock in an area with starthistle.
  • Move the livestock before they damage desired plants.
What's the risk?
Low risk
Possible risk of exposure or harm from chemicals
NONE

Grazing is an effective way to reduce yellow starthistle canopy and keep it from flowering. For best results, follow up with other control activities.

Grazing Tips

  • Grazing many animals in an area for a short duration reduces plant size and vigor. It also reduces seed production.
  • Graze heavily at least 2 times per year to prevent flowering. Several years of grazing will deplete the yellow starthistle seeds in the soil.
  • Goats eat yellow starthistle in the spiny stage. Grazing goats in the flowering stage may only require one treatment per year.
  • Avoid overgrazing the area. Don’t allow more than half of the grass forage to be removed, otherwise it may knock back the grass’s recovery and ability to shade out starthistle.
 
D

Biological Control

Non-Chemical Method

Charles Turner, USDA Agricultural Research Service, Bugwood.org

Biological Control

  • Several insects feed on yellow starthistle. A plant disease hinders yellow starthistle growth. Both play a vital role in regional long-term control.
  • For example, the yellow starthistle hairy weevil (Eustenopus villosus), shown in the photo, reduces seed production by 70 percent or more.
Does it work?
Somewhat effective
  • Biological control on its own won’t get rid of yellow starthistle. Combine this approach with other control methods.
  • Use preventive measures for best results.
How much effort?
Moderate effort
  • Collect insects from an established stand of yellow starthistle.
  • Distribute the insects on yellow starthistle plants at your site.
  • Monitor your site for biocontrol insect activity.
What's the risk?
Low risk
Possible risk of exposure or harm from chemicals
NONE
Fly larva in yellow starthistle flower

Gary L. Piper, Washington State University, Bugwood.org

The larvae of the yellow starthistle peacock fly (Chaetorellia australis) tunnel through the seed head. They damage the seeds.

Early rust fungus infection on yellow starthistle leaves

Eric Coombs, Oregon Department of Agriculture, Bugwood.org

A rust fungus (Puccinia jaceae var. solstitialis) grows on yellow starthistle leaves and stems. It has a negative impact on photosynthesis and nutrient transport, which weakens the plant.

Biological Control Tips

  • These insects are host-specific. They don’t harm native plants or valuable crops.
  • The insects and rust already occur in most areas with yellow starthistle infestations.

Biological Control Reference

For more information about biocontrol for yellow starthistle, see Weed Biological Control  (Oregon Department of Agriculture).

 
E

Herbicides Triclopyr & Glyphosate

Chemical Method: Use with caution

iStock

Herbicides Triclopyr & Glyphosate

Use if Necessary

Herbicides that contain the active ingredients triclopyr and glyphosate effectively control yellow starthistle when used according to label directions.

Does it work?
Effective
  • Several years of monitoring and effort are required to get rid of yellow starthistle.
  • Use preventive measures for best results.
How much effort?
Moderate effort
  • Treat individual yellow starthistle plants and patches.
  • Return to the area each year and take action as needed.
What's the risk?
Low risk
  • Herbicides come with real risks. ALWAYS read the entire label front to back. Review instructions even for brands you know.
  • Herbicides can run off your site into waterways and may harm wildlife. See How to Keep Pesticides Out of Waterways.
Possible risk of exposure or harm from chemicals
Using herbicides includes some amount of risk. The lowest risk comes with using alternative methods.

You may be exposed to an herbicide if you:

  • Get it on your skin
  • Breathe it in
  • Eat or smoke afterward without washing hands
  • Touch or eat plants that are wet with spray (you, pets, or children)
  • Bring it inside on your shoes or clothes

Follow directions closely to reduce risk.

Herbicides with active ingredients triclopyr and/or glyphosate, used individually or in a mixture, are effective chemical treatments for yellow starthistle. Look for these chemical names in the “Active Ingredients” section of product labels.

Photo of herbicide label highlighting active ingredient triclopyr

Weston Miller, Oregon State University

  • The white box on the example product label highlights active ingredient triclopyr. The text on the label states “Kills completely.”
  • Triclopyr doesn’t injure most grasses. It is a good choice for treating yellow starthistle growing next to desired grasses in lawn, pasture, and meadow areas.
Photo of herbicide label highlighting active ingredient glyphosate

Weston Miller, Oregon State University

  • The white box on the example label highlights active ingredient glyphosate. Text on the label states “Kills grass and weeds around flower beds, trees, shrubs....”
  • Glyphosate will damage most plants and grasses. Don’t let the spray contact plants you want to keep.
Yellow starthistle plant before flowering

Mary Ellen (Mel) Harte, Bugwood.org

Herbicides are most effective when when applied to yellow starthistle before the flowering stage as shown in the photo.

Herbicide Application Tips

  • Dicamba is also effective at controlling yellow starthistle. It is often found in products premixed with other similar ingredients such as 2,4-D.
  • Seedlings are killed with a single herbicide application.
  • Repeated applications over 2–3 years will eliminate established yellow starthistle stands.
  • Herbicide applications are most effective for seedlings and small rosettes when they are actively growing and the soil is moist.
  • For best results with a single treatment, apply herbicides late in the rainy season using a high herbicide rate based on label instructions.
  • Return to the treated area and look for regrowth and re-treat as needed.
  • Preemergent herbicide products work to keep yellow starthistle seeds in the soil from germinating.
  • Yellow starthistle will likely re-invade unless you take steps to encourage or plant desirable vegetation.
Minimize the potential impact of herbicides to bees and other pollinators. Treat yellow starthistle plants before they flower. Or apply herbicides in the morning or evening when bees are less active. Avoid spraying pollinators directly. For more information, see OSU’s How to Reduce Bee Poisoning from Pesticides  
 

If Using Herbicides, Protect Yourself & Minimize Risks

Chemical Method: Use with Caution
Great blue heron in marsh

BrianLasenby, iStock

Why is it important to read herbicide labels?

  • They have detailed information on how to use the product correctly and legally.
  • They contain information on potential hazards of the product.
  • They provide instructions you should follow for poisonings and spills.
  • Following label instructions helps you to minimize the risks and maximize the benefits.

Key Herbicide Safety Tips

  • Read the entire label front to back.
  • Follow the instructions.
  • Review the instructions even for brands you know.
  • Only apply the product where the label says it may be applied.
  • Be precise in your application. More is not better.

The Label is the Law

ALWAYS read the label before using herbicide products. The label is a legal document that provides information on how to safely use the herbicide. This helps avoid harm to human health and the environment. Using an herbicide in off-label ways is illegal. It can result in legal enforcement actions.

READ THE LABEL & Follow Instructions
It has instructions to protect you and the environment.

  • Labels are different for every product and they often change over time.
  • Use a magnifying glass for small print.
  • Pay attention to CAUTION, WARNING, and DANGER statements.
  • Pay attention to the PRECAUTIONARY STATEMENTS.
  • The law states you must read and follow herbicide instructions.

Protect Yourself
Eye, skin & lung irritants

  • Wear the right protective gear. This often includes chemical-resistant gloves, safety glasses, a long-sleeve shirt, pants, socks, and shoes.
  • Mix outdoors or in a well-ventilated area.
  • Wash hands after mixing or applying, and before eating or smoking.
  • Take a shower immediately after handling herbicides.
  • Wash clothes worn while mixing or applying separately from other laundry.

Protect Children & Pets
Children and pets are at risk if they eat or touch the plants before it dries.

  • Keep them away during and after applying herbicides (read label for how long).
  • Remove toys and pet dishes from yard before applying.
  • Don’t track herbicide products into your home on shoes or clothes.

Protect Plants You Want to Keep

  • Glyphosate and similar herbicide ingredients damage both grass and broadleaf plants.
  • Minimize spraying of foliage, stems, exposed roots, or the trunks of desirable shrubs or trees to avoid harm.
  • Follow the label to avoid damaging the roots of trees and shrubs.

Avoid Wet, Windy, or Hot Weather
Use during favorable weather for best results.

  • Don’t spray when it’s raining or when rain is expected in the next 24 hours.
  • Wind causes spray to drift that can get on you and desired plants.
  • Herbicides may be less effective in hot weather if the target plants are moisture-stressed.
  • Some herbicides can turn into a vapor in hot weather and damage nearby plants.

Protect Pollinators

  • Apply in the early morning or evening when bees are less active.
  • Kill weeds before they flower. Avoid spraying flowering plants.
  • Do not spray on bees or insects.

Storage & Disposal

  • Store in a secure area away from children.
  • Don’t put unused herbicide products in the trash.
  • Never pour down any drain or waterway.
  • Take unused herbicides to a hazardous waste facility.

Call  1-800-CLEANUP (1-800-253-2687) to find out where to dispose of herbicides.

For the Portland metro region in Oregon, contact Metro’s Recycling Information. Call  503-234-3000, email   or visit Metro’s website  

More about:

About Using Pesticides on School Grounds in Oregon

If using pesticides on school grounds, there are special rules in Oregon. See School Integrated Pest Management  (Oregon Department of Agriculture).

NEED HELP?

The National Pesticide Information Center (NPIC)  can answer questions about pest control chemicals.
 1-800-858-7378 or npic@ace.orst.edu  

Consider using a licensed pest or weed control company. Learn How to Hire a Pest Control Company.

Your local Extension Specialist in Oregon  and other states  can suggest other methods.

Invasive Species Alert

  • Invasives are non-native species that spread aggressively and alter the environment.
  • Controlling unwanted yellow starthistle is costly.
  • Please do your part to control it on property you manage. It can spread beyond your property and impact your neighbors.

If you think you’ve found yellow starthistle in the grey areas of this map, please report it to the Oregon Invasive Species Hotline at:  1-866-INVADER (1-888-468-2337) or use their online reporting form  

open Map static invasive map
Invasive species data @ 2022, iMapInvasives (NatureServe)

If you find yellow starthistle in a new area (orange shows already reported cases), please report it  

View Larger Map >

Content provided by editor Weston Miller and writer J. Jeremiah Mann. Pesticide safety information edited by Kaci Buhl.

 Peer reviewed by OSU Department of Horticulture.

Photo of Weston Miller

Weston Miller

Project Founder and Content Writer

Weston Miller served as Community and Urban Horticulture faculty for Oregon State University Extension Service for Clackamas, Multnomah, and Washington Counties. Weston is an author for content for this website. He developed funding partnerships with Portland area agencies to initiate and build out the Solve Pest Problems website focused on this goals:

J. Jeremiah Mann

J. Jeremiah Mann

J. Jeremiah Mann completed a Physical Science undergraduate degree at Humboldt State University, and M.S, Ph.D focusing on plant science topics at UC Davis. He went on to work for the Natural Resources Conservation Service and in a leadership position serving a private agricultural technology company. He currently lives in Sacramento California where he consults on pest and property management topics.

Photo of Kaci Buhl

Kaci Buhl

At the state level, I lead the Pesticide Safety Education Program (PSEP). The program hosts live recertification events around the state, serving over 1,000 licensed pesticide applicators each year. We also produce web-based training modules and license-preparation study manuals. Special training for unlicensed pesticide applicators is also available through a grant from the USDA Specialty Crop Block Grant Program. The PSEP at OSU works closely with the Oregon Department of Agriculture's Pesticides Division.