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Pest SolutionsPESTS + WEEDSUSING PESTICIDES OR HERBICIDES?
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Italian Thistle
Carduus pycnocephalus
Updated Feb 20, 2025
Make a Positive Identification
- Italian thistle lives for one or two years. Seeds germinate with rain and cool weather through early spring.
- Young plants are spiny rosettes and grow a deep tap root.
- In spring and early summer plants grow spiny, winged, erect to spreading stems 1-7 feet tall.
- Dense clusters of purple flowers form at the tips of the stems.
Species: Italian thistle
"carduus-pycnocephalus-1" by Friends of Chiltern Mt Pilot National Park is licensed under CC BY-NC-SA 2.0
Italian thistle plants quickly dominate invaded areas. Single plants may produce many hundreds of seeds.
Species: Italian thistle
"Carduus pycnocephalus leaf3" by Harry Rose is licensed under CC BY 2.0
Stems are often 6 feet tall at full bloom and have spiny wings. Spiny leaves have 4-10 lobes. They are smooth and green above. The lower surface is hairy with white spots.
Species: Italian thistle
Zeynel Cebeci, CC BY-SA 4.0 via Wikimedia Commons
Blooming stems branch near the top. They form clusters of 1-5 pink to purple flowers covered with sharp spines. The flowers are cylinder-shaped.
Species: Italian thistle
Joseph M. DiTomaso, University of California - Davis, Bugwood.org
Seedlings germinate in fall and winter. They form spiny rosettes with deep taproots.
Species: Italian thistle
Philmarin, CC BY-SA 4.0, via Wikimedia Commons
Seed color is golden to brown with many veins. Seeds are hairless and less than ¼ inch long. They are carried by air currents on fluffy white plumes. Most seeds are viable and germinate within a year. Buried seeds can remain viable in the soil for 3 years.
LOOK-ALIKES: SLENDERFLOWER THISTLE AND CANADA THISTLE
Species: Slenderflower thistle
"carduus-tenuiflorus-4" by Friends of Chiltern Mt Pilot National Park is licensed under CC BY-NC-SA 2.0
Italian thistle is similar to slenderflower thistle. Slenderflower thistle leaves have 12-20 lobes, compared to 4-10 lobes with Italian thistle. The flower heads are dense, with 5-20 flowers per cluster.
Management strategies for Italian thistle and slender thistle are the same.
Species: Canada thistle
"Cirsium arvense" by Matt Lavin is licensed under CC BY 2.0
Both Italian thistle and Canada thistle have hairy green leaves and stems. Italian thistle stems are winged; Canada thistle's are not. The plants look different when they flower. Canada thistle flowers are globe shaped (see photo). Italian thistle flowers are shaped like a cylinder.
See How to Get Rid of Canada thistle.
Italian Thistle Benefits
- Italian thistle flowers attract pollinators, especially bees.
Italian Thistle Risks
- Italian thistle spreads quickly with seeds. It is difficult to control.
- It degrades wildlife habitat and livestock forage if left unmanaged.
- Italian thistle can displace desired vegetation and dominate an area if not controlled.
- Its spiny leaves and flowers limit grazing animals and human activity. Grazing animals avoid Italian thistle.
Risk Card
Does it cause harm?
Adults & Children
Low
Prickly flowers and leaves hurt and limit access to areas
Property
High
Dominates an area when left unmanaged
Pets
None
Annoyance
High
Difficult to control
Environment
High
Rapidly spreading to new areas and taking over
Action Recommended
Take Action
If you have Italian thistle on your property, take action to control it right away.
Do I need to take action?
Yes. Remove individual plants and small patches of Italian thistle. Both small and large patches require several years of attention to control.
What if I do nothing?
Italian thistle can dominate an area when left unmanaged.
PREVENT ITALIAN THISTLE
Joseph M. DiTomaso, University of California - Davis, Bugwood.org
Look for Newly Germinated Seedlings followed by Rosettes
- Look for seedlings and rosettes in the late fall, winter, and early spring.
- Take note of their location and plan to treat plants.
- Continue to monitor the area each year. Control it as needed.
Weston Miller, Oregon State University
Remove Dirt from Shoes and Equipment
- After working or traveling in an area that has Italian thistle seeds, clean your boots and tools. Use a wire brush to remove all soil that may contain seeds or root fragments.
- If you drive into an Italian thistle stand, clean your vehicle before traveling into new areas. Seeds are easily transported to new locations on vehicles and equipment.
"native grass-prairie restoration_southwest research center_0013" by Mizzou CAFNR is licensed under CC BY-NC 2.0
Replant Larger Areas with Technical Support
- Italian thistle is difficult to eliminate 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.
Solutions for Italian Thistle
Early Detection & Rapid Response
- Italian thistle seeds travel on air currents. They are carried to new areas on contaminated vehicles, soil, or livestock.
- Plants prefer fertile soil. It invades grasslands, pastures, woodlands, and roadsides tolerating a wide variety of soil types.
- Look for new infestations on your property. Control it before it sets seed and becomes a bigger problem.
Physically Remove Plants & Non-Chemical Options
- Hand tools are effective in removing individual plants and small patches.
- Mowing plants in the early flowering stage may reduce seed production.
- Cultivation that cuts the taproot reduces or eliminates flowering. This helps to control patches of Italian thistle.
- Mowing or cultivation alone will not effectively control Italian thistle.
Herbicides (Weed Killers)
- Herbicides control Italian thistle when used according to the label instructions.
Monitoring & Follow-Up
- Established patches are difficult to control. It requires at least 3 years of control actions and monitoring to get rid of Italian thistle.
- Return to Italian thistle patches following control activities. Look for regrowth.
- Look for rosettes in the winter and early 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 Physical removal |
Effective |
Low risk |
Recommended |
B Cultivation and Mowing |
Effective |
Low risk |
Recommended |
C Biological Control |
Somewhat effective |
Low risk |
|
D Control with Herbicides |
Effective |
Moderate risk |
Use if Necessary |
|
E If Using Herbicides, Protect Yourself & Minimize Risks
|
A
Physical removal
Non-Chemical Method
Weston Miller, Oregon State University
Physical removal
Recommended
- Dig out individual plants and small patches in winter or early spring when seedlings and rosettes are present.
- This works best when soil is drying and no rain or irrigation will follow control action.
| Does it work? | Effective
|
| How much effort? | High effort
|
| What's the risk? | Low risk |
| Possible risk of exposure or harm from chemicals | NONE |
B
Cultivation and Mowing
Non-Chemical Method
sshepard, iStock
Cultivation and Mowing
Recommended
- Cultivate and/or mow patches of Italian thistle to keep plants from flowering and setting seed.
| Does it work? | Effective
|
| How much effort? | High effort
|
| What's the risk? | Low risk |
| Possible risk of exposure or harm from chemicals | NONE |
Cultivating ITALIAN thistle TIPS
- Cultivate Italian thistle after the last rains and before flowering for best results. If you cultivate it too early (before the last rains), more seeds will sprout.
- Cultivation will have to be repeated regularly to keep plants from blooming and setting seed.
- Manage pastures to reduce bare ground. This will limit Italian thistle establishment.
Soil Disturbance & Erosion
- Tilling large patches of established plants with disk attachment creates significant soil disturbance.
- Minimize soil disturbance as much as possible.
- Regrade the soil after digging out plants. Apply mulch (when appropriate).
- Take steps to prevent erosion as needed.
- Replant the area to outcompete Italian thistle seedlings.
Mowing ITALIAN thistle
- Carefully timed mowing will not kill plants. However, mowing limits Italian thistle seed production.
- Mow when flowerheads are present, but before they fully open.
- Plants will regrow stems and flowers following mowing. Follow-up treatment will be needed.
C
Biological Control
Non-Chemical Method
Eric Coombs, Oregon Department of Agriculture, Bugwood.org
Biological Control
- The thistle crown root weevil (Trichosirocalus horridus) is established in Oregon. The photo shows the root weevil larva feeding on a thistle stem and damaging the plant.
- You can collect insects at one location and release them in your patch of Italian thistle.
- Before collecting and distributing biocontrol insects in Oregon, see Weed Biological Control – Oregon Department of Agriculture and talk to your local OSU extension agent.
| Does it work? | Somewhat effective
|
| How much effort? | Moderate effort
|
| What's the risk? | Low risk |
| Possible risk of exposure or harm from chemicals | NONE |
Biological Control Reference
For more information about biocontrol for Italian thistle, see Weed Biological Control (Oregon Department of Agriculture).
D
Control with Herbicides
Chemical Method: Use with caution
iStock
Control with Herbicides
Use if Necessary
| Does it work? | Effective
|
| How much effort? | Moderate effort
|
| What's the risk? | Moderate risk
|
| 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:
Follow directions closely to reduce risk. |
Some herbicides are available for home use. A few are listed below. These active ingredients are available alone or in products containing more than one. They are effective chemical treatments for Italian thistle. Look for these chemical names in the “Active Ingredients” section of product labels.
- Dicamba
- Glyphosate, Isopropylamine salt
- Triclopyr
- Imazapyr
- 2,4-D
Suggested active ingredients are from the Pesticide Information Center Online (PICOL) Database. They are permitted for HOME use in Oregon. Read the label for application directions and effectiveness information.
ONLY professional pesticide applicators can use Restricted-Use Pesticides (RUP) that may be more effective. For larger stands of Italian thistle contact a licensed pesticide applicator with experience controlling Italian thistle.
"Carduus pycnocephalus L. subsp. pycnocephalus" by Andrea Moro, © Department of Life Sciences, University of Trieste is licensed under CC-BY-SA 4.0
Herbicide Application Tips
- Most of these ingredients will damage most plants and grasses. Don’t let the spray contact plants you want to keep.
- Apply herbicides on seedlings and small rosettes. Herbicides are most effective when the plants are actively growing, and the soil is moist.
- Seedlings may be killed with a single herbicide application.
- Repeated applications over 2-3 years will reduce or eliminate established Italian thistle stands. However, dormant seeds may germinate after 3 years. Follow-up site visits will be needed.
- For best results with a single treatment, apply herbicides late in the rainy season. Use a high herbicide rate based on label instructions.
- Return to the treated area and look for regrowth. Re-treat as needed.
- Pre-emergent herbicide products work by preventing Italian thistle seeds in the soil from germinating.
- Italian thistle will re-grow unless you take steps to encourage or plant desirable vegetation.
Minimize the potential impact of herbicides on bees and other pollinators. Treat Italian thistle 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
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. It includes appropriate personal protective gear and application methods. 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, but is not limited to: a long-sleeved shirt, pants, socks, closed shoes, safety glasses, and chemical-resistant gloves.
- 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 they dry.
- Keep them away during and after applying herbicides (read the label for how long).
- Remove toys and pet dishes from the yard before applying.
- Don’t track herbicide products into your home on shoes or clothes.
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.
Protect Plants You Want to Keep
- Glyphosate and other broad-spectrum herbicide ingredients can 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 the spray to drift, which 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.
Don’t Spray into Water
- It’s illegal to apply herbicides in a stream or slow-moving/wetland pool.
- You need a product registered for aquatic areas. This includes waterways, ditches, drains, and other places where water collects.
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 Italian thistle 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 Italian thistle 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
Invasive species data @ 2022, iMapInvasives (NatureServe)
View Larger Map >
If you find Italian thistle in a new area (orange shows already reported cases), please report it
Content provided by editors Signe Danler and Weston Miller, and writer J. Jeremiah Mann. Pesticide safety information edited by Kaci Buhl.
Peer review facilitated by OSU Department of Horticulture.
Italian Thistle References
Italian Thistle
Washington State Noxious Weed Control Board
Problem Thistles of Oregon
Oregon State University
Plumeless, musk, Italian, and slenderflower thistle
Weed Control in Natural Areas in the Western United States