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Giant Hogweed

Heracleum mantegazzianum
Updated Mar 29, 2024
 
1

Make a Positive Identification

  • Giant hogweed plants often reach 10–12 feet in height. The white flowers grow 8–24 inches across.
  • Leaves are 3–5 feet wide, coarsely toothed, with deeply cut leaflets.
  • Giant hogweed spreads by seeds. A single plant produces up to 20,000 seeds. Seeds move via water and wind to new locations.
Giant hogweed is a health hazard to humans and other animals  Giant hogweed sap on your skin or eyes causes severe burns when exposed to sunlight. This can cause blistering, painful burns, or severe eye damage. Don’t touch giant hogweed plants or try to control them on your own.

 

Required Reporting in the Pacific Northwest

Report the location of giant hogweed. In Oregon and Washington, state laws require property owners to report it.

  • If you think you’ve found giant hogweed anywhere in Oregon, please report it to the Oregon Invasive Species Hotline at:  1-866-INVADER (1-888-468-2337) or use their online reporting form  
  • If you think you’ve found giant hogweed anywhere in Washington, Find Your County Weed Board 

Early Detection Rapid Response

Giant hogweed is regarded as an EDRR (early detection, rapid response) species. Natural resource agencies across the Pacific Northwest are coordinating efforts to manage known populations and limit the spread of this invasive plant.

An agency will follow up with you and make arrangements to control it on your property when you report a new infestation of giant hogweed. The goal is to keep this plant from establishing in the Pacific Northwest.

Giant Hogweed
Species: Giant Hogweed
Giant hogweed with three large flower stalks

Terry English, USDA APHIS PPQ, Bugwood.org

Giant hogweed plants often grow 10–12 feet tall. 

Species: Giant Hogweed
Giant hogweed flowers

Terry English, USDA APHIS PPQ, Bugwood.org

They have white, umbrella-like, flowerhead (umbels) that are 18–24 inches across.

Species: Giant Hogweed
Hollow stem is covered with dark purple blotches, bumps, and hairs

Giant hogweed stems are 2–4 inches in diameter and hollow. They have purplish-red blotches and bumps, and are covered with stiff hairs.

Species: Giant Hogweed
Giant hogweed leaves

Terry English, USDA APHIS PPQ, Bugwood.org

Leaves are 3-5 feet wide, coarsely toothed, with deeply cut leaflets.

Species: Giant Hogweed
Dense patch of giant hogweed plants before flowering

Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Giant hogweed forms dense patches that emerge in later winter and spring. Stems die and remain standing late summer through early winter.

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LOOK-ALIKE: COW PARSNIP
Species: Cow Parsnip
Cow parsnip plant with white flowers

Shaun Winterton, Aquarium and Pond Plants of the World, Edition 3, USDA APHIS PPQ, Bugwood.org

The native plant cow parsnip (Heracleum maximum) often forms dense patches. However, individual plants are smaller than giant hogweed (no larger than 7 feet tall). Leaves are 2 feet or less across with less ragged edges. Sap causes severe burns.


Tolerate if possible

This native plant does not require removal or reporting.

 
2

Giant Hogweed Benefits

Giant hogweed is an invasive weed. It doesn’t have any benefits for people or the environment.

 

Giant Hogweed Risks

  • Giant hogweed quickly grows into large patches.
  • It crowds out understory plants.
  • During late summer, the stems die. This leaves the soil surface bare and prone to erosion.
  • Sap from broken stems causes skin sensitivity to sunlight. This may result in severe burns, blisters, and rashes. Contact with the eye can lead to severe damage.
Risk Card
Does it cause harm?
Adults & Children
Very High
Property
High
Pets
Very High
Annoyance
Very High
Environment
High
Action Highly Recommended
 
3

Take Action

If you have giant hogweed on property you manage, take action to report it. Agencies can help you control this invasive plant on your property.

Do I need to take action?
Yes. Report the plant location. If the plant is growing on your property, a natural resource professional will help you to create a control plan.

What if I do nothing?
Giant hogweed will spread by seed and take over areas. You will be out of compliance with your state’s invasive species reporting requirements.

 
4

Prevent Giant Hogweed

Giant hogweed shoots with young leaves emerging from soil

Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Watch for Giant Hogweed
  • Look for giant hogweed seedlings and new growth during the late winter and early spring following control actions.
  • Plan control actions in winter or early spring and flower removal in summer. Continue to monitor the area each year.
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 giant hogweed seeds in the soil, clean your boots and tools. Use a wire brush to remove all soil that may contain seeds.
  • If you drive into a giant hogweed stand, clean your vehicle.
Landscape area with native plants growing densely together

Weston Miller, Oregon State University

Install New Plants
  • Take care of the plants to get them established and to suppress giant hogweed regrowth.
  • Replanting stabilizes the soil surface, shades out giant hogweed seedlings, and creates habitat.
  • Giant hogweed presence and removal activities may significantly damage a site. There may be few or no desirable plants remaining.
  • Plan for at least 2-3 years of monitoring and maintenance.
  • Your local extension specialist, soil and water conservation district, or a professional re-vegetation specialist can suggest strategies for your area.
 
5
Solutions for Giant Hogweed

Early Detection and Rapid Response

  • Watch for giant hogweed on property you manage. Take action to identify and report it.
  • Remove it before it becomes a bigger problem. It spreads quickly.
  • Look for giant hogweed leaves in early spring and flowers in summer.
  • Act before or during its flowering period, before it sets seeds.

Physically Remove Plants and Non-Chemical Options

Dig out individual plants. Dispose of mature seed heads in the trash.

Herbicides (Weed Killers)

Herbicides effectively control giant hogweed when used according to the label instructions.

Monitoring and Follow-Up

Return to the stand and look for regrowth in winter and early spring. Control giant hogweed as needed each year.

Get Help From Natural Resource Professionals

We recommend working with a natural resource professional who will help you to create a control plan for removing giant hogweed on your property.

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 Plants
Very effective
High risk
B
Herbicides Triclopyr and Glyphosate
Effective
Moderate risk
Use if Necessary
C
If Using Herbicides, Protect Yourself & Minimize Risks
 
A

Physically Remove Plants

Non-Chemical Method

Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Physically Remove Plants

Dig out small patches of giant hogweed with a sharp spade or shovel. Cut each plant below the root crown as shown in the photo.

Does it work?
Very effective
  • Control of giant hogweed requires several years of monitoring and treatment. Seeds in the soil sprout and grow when mature plants are killed.
  • Use preventive measures for best results.
How much effort?
Moderate effort

Dig up seedlings and small plants. Remove the root crown.

What's the risk?
High risk

Giant hogweed sap on your skin or eyes causes severe burns when exposed to sunlight. It can result in blistering, painful burns, or severe eye damage. Don’t touch giant hogweed plants or try to control them on your own.

Possible risk of exposure or harm from chemicals
NONE

We recommend working with a natural resource professional who will help you to create a control plan for removing giant hogweed on your property.

Several dug-up giant hogweed plants

Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

In early spring, cut larger individual plants below the root crown. Dig up seedlings and small plants. Remove root crowns from the site to keep them from re-growing.

Giant Hogweed Removal Tips

  • In early spring, cut larger individual plants below the root crown. Dig up seedlings and small plants. Remove root crowns from the site to keep them from re-growing.
  • Leaves and stems can be left on the ground to decompose.
  • Remove flowers before seeds mature.
  • Place mature seed heads in a sturdy plastic bag. Put the bag in the trash.
  • Do not compost the seed heads.
  • Don’t use a string trimmer on giant hogweed. The sap may get on you and cause injury.
Giant hogweed seed head in black plastic bag

Thomas B. Denholm, New Jersey Department of Agriculture, Bugwood.org

  • Put mature seed heads in a sealable plastic bag and dispose of the bags in the trash or a landfill. Don’t put mature seed heads in the green waste bin.
  • Revisit plants and remove additional seed heads that mature later in the year.
 
B

Herbicides Triclopyr and Glyphosate

Chemical Method: Use with caution

Terry English, USDA APHIS PPQ, Bugwood.org

Herbicides Triclopyr and Glyphosate

Use if Necessary

Herbicide products containing active ingredients glyphosate and triclopyr are effective treatments for giant hogweed when label directions are followed.

Does it work?
Effective
  • Control of giant hogweed requires several years of monitoring and treatment. Seeds in the soil sprout and grow when mature plants are killed.
  • Use preventive measures for best results.
How much effort?
Moderate effort
  • Treat individual giant hogweed plants and patches.
  • Return to the area each year and take action as needed.
What's the risk?
Moderate 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.

  • We recommend getting help from a licensed pesticide applicator with experience controlling giant hogweed.
  • If you choose to do it yourself, natural resource management professionals use herbicide products that contain triclopyr and glyphosate. These products, used individually or in a mixture, are effective chemical treatments for giant hogweed.
Photo of herbicide label highlighting active ingredient triclopyr

Weston Miller, Oregon State University

A white box on this example product label highlights active ingredient triclopyr. Text on the label states “Kills completely - stumps and roots won’t grow.”

Triclopyr doesn’t injure most grasses. It is a good choice for treating giant hogweed growing next to desired grasses in lawn, pasture, and meadow areas.

Photo of herbicide label highlighting active ingredient glyphosate

Weston Miller, Oregon State University

A 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.

Herbicide Application Tips

  • Apply herbicides in winter or early spring before or after giant hogweed starts to flower.
  • Optimal application timing is during the rapid growth of leaves.
  • It will take several weeks for the treated plants to die.
  • Monitor the area and repeat treatment each year as needed.
  • Giant hogweed often grows near water. Herbicide application permits may be required for riparian areas.
 

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.

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.
  • Control of unwanted giant hogweed is costly.
  • Please do your part to control it on property you manage. It can spread beyond your property and have an adverse impact on your neighbors.
  • Giant hogweed is regarded as an EDRR (early detection, rapid response) species. Agencies across the Pacific Northwest are coordinating efforts to manage known populations and limit the spread of this invasive plant.

Report the location of giant hogweed. In Oregon and Washington, state laws require property owners to report it.

  • If you think you’ve found giant hogweed anywhere in Oregon, please report it to the Oregon Invasive Species Hotline at:  1-866-INVADER (1-888-468-2337) or use their online reporting form  
  • If you think you’ve found giant hogweed anywhere in Washington, Find Your County Weed Board 
open Map static invasive map
Invasive species data @ 2022, iMapInvasives (NatureServe)

If you find giant hogweed anywhere in Oregon, please report it   Reporting giant hogweed is required.

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.