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Yellow Flag Iris

Iris pseudacorus
Updated Nov 15, 2023
 
1

Make a Positive Identification

  • Yellow flag iris is an iris with yellow flowers and typical, sword-shaped leaves.
  • It spreads quickly and forms dense stands in shallow water and wet soil as shown in the photo above.
Species: Yellow flag iris
Clump of yellow flag iris leaves

John Ruter, University of Georgia, Bugwood.org

The mature leaves are 2–3 feet long, flattened and sword-shaped, typical of most iris. They may stay evergreen in mild winters.

Species: Yellow flag iris
Yellow flag iris flower

Yellow iris (Iris pseudacorus) by Evelyn Simak - geograph.org.uk/p/6172667 is licensed under CC-by-sa/2.0.

Yellow flag iris flowers have 3 large downward-spreading sepals (flower part on outside) and 3 small erect petals. The sepals may have delicate brownish to purple veins. The yellow color may be bright or pale. It blooms from late spring into summer.

Species: Yellow flag iris
Glossy green seed pod

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

The seed pod is up to 4 inches long and glossy green. It contains many flattened brown seeds. Seed pods float on the water, and spread yellow flag iris seeds to new locations.

Species: Yellow flag iris
Rhizome with leaves and roots

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

Yellow flag iris spreads by stout rhizomes. They grow rapidly and form a dense mat.

Species: Yellow flag iris
Brown, flattened seeds

Steve Hurst, USDA NRCS PLANTS Database, Bugwood.org

Flattened brown seeds are about ¼ inch in diameter.

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LOOK-ALIKES: CATTAIL, BURR-REED
Species: Cattail
Cattail leaves shown are round at base

Bruce Ackley, The Ohio State University, Bugwood.org

Yellow flag iris leaves can be confused with cattails (Typha spp.). Cattails are round at the base and taller than yellow flag iris. Iris leaves are flattened along one plane and shorter.


Helpful

Cattails are native, wetland plants. They provide habitat and help protect stream and pond banks from erosion. Tolerate cattail, if possible. However, control is sometimes necessary for stream banks. See Controlling Cattails  (Cornell University).

Species: Bur-reed
Bur-reed leaves

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

Yellow flag iris may also be mistaken for native bur‐reeds (Sparganium spp.). Bur-reeds have thick, spongy leaves that are narrower than iris leaves.


Helpful

Bur‐reeds are native, wetland plants. They provide habitat and help protect stream and pond banks from erosion. Tolerate bur‐reeds, if possible.

 
2

Yellow Flag Iris Benefits

  • Yellow flag iris is an invasive weed. It doesn’t have any benefits for people or the environment.
 

Yellow Flag Iris Risks

  • Yellow flag iris forms dense stands in wet areas. It crowds out desired vegetation. It is difficult to control.
  • It degrades native fish habitat and bird nesting and rearing sites.
  • Yellow flag iris quickly overwhelms shallow ponds and stream edges. It clogs ditches and irrigation canals.
  • Its sap causes skin irritation or blistering.
  • Yellow flag iris is toxic to livestock.
Risk Card
Does it cause harm?
Adults & Children
Some
Property
High
Pets
Low
Annoyance
High
Environment
High
Action Highly Recommended
 
3

Take Action

If you have yellow flag iris 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 flag iris before they become a bigger problem. Established patches require several years of attention to control.

Yellow flag iris is a popular ornamental plant and widely sold at nurseries, plant sales, and online. Don’t buy this invasive species or plant it in your landscape.

What if I do nothing?
Yellow flag iris spreads quickly and is difficult to control. It takes over neglected areas.

 
4

Prevent Yellow Flag Iris

Yellow flag iris leaves resprouting

Leslie J. Mehrhoff, University of Connecticut, Bugwood.org (cropped)

Look for New Growth and Yellow Flowers
  • After you dig out yellow flag iris or treat it with herbicide, watch for new growth emerging from rhizomes in early spring.
  • Seeds may also sprout to create new plants.
Gloved hands using metal brush to clean boots


Weston Miller, Oregon State University

Remove Dirt from Shoes and Equipment
  • After working or traveling in an area with yellow flag iris, clean your boots and tools.
  • Use a wire brush to remove all soil that may contain seeds.
  • Use a pressure washer to clean vehicles and heavy equipment after working in an infested area. Don’t work at a new site until the equipment is cleaned.
Dense stand of red-osier dogwood

Richard Webb, Bugwood.org

Replant the Area
  • Following control activities, plant vigorous riparian plants such as native willow (Salix spp.) and red-osier dogwood (Cornus sericea). These will suppress yellow flag iris growth.
  • Planting these riparian species also provides erosion control in treated areas.
  • Yellow flag iris is difficult to eradicate from an infested area. Replanting a previously infested area requires planning and effort.
  • Create a multi-year revegetation plan. The plan should include site preparation and planting details, plant care, and follow-up control for yellow flag iris and other weeds. Plan for at least 2–3 years of monitoring and maintenance.
  • Your local extension specialist, soil and water conservation district, or a professional revegetation specialist can suggest strategies for your area.
 
5
Solutions for Yellow Flag Iris

Early Detection and Rapid Response

  • The best yellow flag iris management strategy is to find small patches and control them before they become a bigger problem.

Physical Removal of Plants and Non-Chemical Methods

  • It requires repeated effort over several years to get rid of a large, established stand of yellow flag iris. Persistence is worthwhile to get rid of this invasive aquatic species.
  • Digging out plants works for individual plants and small clumps.
  • For larger patches, kill plants with a covering of thick, synthetic tarps, light-impermeable landscape fabric, or geotextile fabric products.

Herbicides (Weed Killers)

  • Herbicides effectively control yellow flag iris when used according to the label directions.

Monitoring and Follow-Up

  • Monitor your property each year for yellow flag iris. Take action as needed.
  • If this plant is allowed to establish, stands are difficult to control. It requires annual management to keep it from spreading.
  • Yellow flag iris disperses with floating seeds. Once established, it spreads with robust rhizomes.

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
Effective
High risk
B
Tarping
Somewhat effective
Low risk
C
Herbicides Glyphosate and Imazapyr for Non-aquatic Areas
Effective
Moderate risk
Use if Necessary
D
Herbicide Products for Aquatic Areas
Effective
Moderate risk
Use if Necessary
E
If Using Herbicides, Protect Yourself & Minimize Risks
 
A

Physically Remove

Non-Chemical Method

Weston Miller, Oregon State University

Physically Remove

  • Dig out small patches. Large patches can be smothered with a tarp.
  • Burning is not recommended for large patches. Seeds germinate and grow well after late summer burning. Plants will re-sprout from rhizomes after burning.
Does it work?
Effective

It takes repeated effort over several years to get rid of a large, established stand of yellow flag iris.

How much effort?
High effort

Remove all of the root pieces. Dispose of the plants in the trash. Do not compost this invasive plant.

What's the risk?
High risk

Sap in the leaves and rhizomes cause skin irritation or blistering.

Possible risk of exposure or harm from chemicals
NONE

Hand digging is practical for single yellow flag iris plants or small patches.

Yellow flag iris rhizome exterior and interior views

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

Rhizome fragments often grow new plants. Carefully remove all rhizome fragments.

Green waste bin on curb

Weston Miller, Oregon State University

  • Put yellow flag iris rhizomes in your green waste bin. Or take them to a local green waste composting facility.
  • Rhizomes will regrow if placed directly in a compost pile.
 
B

Tarping

Non-Chemical Method

"Laying down the weed barrier" by j.bohnsack is licensed under CC BY-SA 2.0 (cropped).

Tarping

  • Small patches of yellow flag iris can be covered with a light-proof barrier. The goal is to deprive the plants of light.
  • Use thick synthetic tarps, landscape fabric, or geotextile fabric.
  • Weigh the covering down at the edges. Be sure to extend the tarp well beyond the edges of the infestation.
Does it work?
Somewhat effective

This method is only practical if you can leave the covering in place for several years.

How much effort?
Moderate effort

Check regularly to make sure plants are not growing up around the tarp.

What's the risk?
Low risk
Possible risk of exposure or harm from chemicals
NONE

Small patches of yellow flag iris can be tarped to block light.

 
C

Herbicides Glyphosate and Imazapyr for Non-aquatic Areas

Chemical Method: Use with caution

Chameleonseye, iStock

Herbicides Glyphosate and Imazapyr for Non-aquatic Areas

Use if Necessary

Herbicides that contain the active ingredients glyphosate and imazapyr effectively kill yellow flag iris when used according to label directions.

Does it work?
Effective

It takes repeated effort over several years to get rid of a well-established stand of yellow flag iris.

How much effort?
Moderate effort
  • Control requires several years of monitoring and treatment.
  • Use preventive measures for best results.
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.

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

Photo of herbicide label that highlights active ingredient glyphosate

Weston Miller, Oregon State University

  • The white box on the example label highlights active ingredient glyphosate. The 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.
Photo of herbicide label highlighting active ingredients glyphosate and imazapyr

Weston Miller, Oregon State University

  • The white box on this example product label highlights active ingredients glyphosate and imazapyr.
  • These ingredients will damage most plants and grasses. Don’t let the spray contact plants you want to keep.

Herbicide Application Tips

  • These ingredients will damage most plants and grasses. Don’t let the spray contact plants you want to keep.
  • Premixed products are available in hardware stores and garden centers.
  • Apply herbicide products to yellow flag iris leaves late spring or fall.
  • Good coverage of foliage is critical for success.
  • Yellow flag iris may take several months to die after an herbicide application.
  • Monitor the area for regrowth and re-treat every year, if needed.

 

Minimize the potential impact of herbicides to bees and other pollinators. Treat yellow flag iris plants before or after they flower. If plants are flowering when you need to treat them, apply 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  

 

 
D

Herbicide Products for Aquatic Areas

Chemical Method: Use with caution

Herbicide Products for Aquatic Areas

Use if Necessary

Aquatic formulas of herbicide products containing active ingredients glyphosate and imazapyr effectively control yellow flag iris when used according to label directions.

Does it work?
Effective

It takes repeated effort over several years to get rid of a well-established stand of yellow flag iris.

How much effort?
High effort
  • Treating yellow flag iris near aquatic areas requires specialized skills to protect waterways.
  • Use preventive measures for best results.
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.

Aquatic formulas of herbicide products that contain active ingredients glyphosate and imazapyr effectively control yellow flag iris when used according to label directions.

Herbicide Application Requirements for Aquatic Areas

  • Herbicides applied over or near a water body must be registered for aquatic use.
  • Treating yellow flag iris near aquatic areas requires specialized skills. This ensures the herbicide is applied effectively. It also protects waterways.
  • Aquatic-use products are rarely sold at plant nurseries or garden centers. They are available through specialty pesticide dealers.
  • Other aquatic-use herbicide products may be legal in your area. Consult a licensed pesticide applicator or your local university extension agent before purchasing or using an aquatic herbicide product.
Consider hiring a licensed pesticide applicator to manage yellow flag iris in aquatic areas.
 

If Using Herbicides, Protect Yourself & Minimize Risks

Chemical Method: Use with Caution
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 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 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.

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 yellow flag iris is costly.
  • Please do your part to control it on property you manage. Yellow flag iris can spread beyond your property and have an adverse impact on your neighbors.

If you think you’ve found yellow flag iris 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)

The map shows the distribution of yellow flag iris (Iris pseudacorus) in Oregon. If you find yellow flag iris in a new area (orange shows already reported cases), please report it.

View Larger Map >

Content provided by editor Weston Miller and writers Signe Danler and 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:

Signe Danler

Signe Danler (Editor/Writer)

Signe Danler is a veteran Master Gardener and landscape designer, with an MAg degree in Horticulture from OSU, and an emphasis on Urban Horticulture. As instructor for the OSU Extension Service online Home Horticulture and Master Gardener Program, she uses her experience and training in gardening, urban forestry and ecological landscaping to communicate about and promote sustainable gardening and landscaping practices.

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.