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Pest SolutionsPESTS + WEEDSUSING PESTICIDES OR HERBICIDES?
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Giant Hogweed
Heracleum mantegazzianum
Updated Mar 29, 2024
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
Terry English, USDA APHIS PPQ, Bugwood.org
Giant hogweed plants often grow 10–12 feet tall.
Species: Giant Hogweed
Terry English, USDA APHIS PPQ, Bugwood.org
They have white, umbrella-like, flowerhead (umbels) that are 18–24 inches across.
Species: Giant Hogweed
"Giant Hogweed Stem" by NYS Department of Environmental Conservation is licensed under CC BY-NC-ND 2.0.
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
Terry English, USDA APHIS PPQ, Bugwood.org
Leaves are 3-5 feet wide, coarsely toothed, with deeply cut leaflets.
Species: Giant Hogweed
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.
LOOK-ALIKE: COW PARSNIP
Species: Cow Parsnip
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.
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
Sap from broken stems causes skin sensitivity to sunlight. Results in severe burns, blisters and rashes. Contact with the eye can lead to severe damage.
Property
High
Quickly grows into large patches
Pets
Very High
Same as for people
Annoyance
Very High
Requires control efforts
Environment
High
Crowds out understory plants
Action Highly Recommended
Take action to report and control this invasive weed.
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.
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.
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.
Jump To
| Method | Does it work? | Is it safe? | Recommendation |
|---|---|---|---|
A Physically Remove Plants |
Very effective |
High risk |
Recommended |
B Herbicides Triclopyr and Glyphosate |
Effective |
Moderate risk |
Use if Necessary |
|
C If Using Herbicides, Protect Yourself & Minimize Risks
|
|||
|
D Prevent Giant Hogweed
|
|||
A
Physically Remove Plants
Non-Chemical Method
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Physically Remove Plants
Recommended
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
|
| 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.
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
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.
Thomas B. Denholm, New Jersey Department of Agriculture, Bugwood.org
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
|
| 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. |
- 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.
Weston Miller, Oregon State University
Weston Miller, Oregon State University
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
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 if needed.
- 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.
Prevent Giant Hogweed
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.
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.
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.
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
Invasive species data @ 2022, iMapInvasives (NatureServe)
View Larger Map >
If you find giant hogweed anywhere in Oregon, please report it Reporting giant hogweed is required.
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.
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