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Indigo Bush

Amorpha fruticosa

Updated Feb 09, 2023

Make a Positive Identification

Indigo bush is an invasive woody shrub with lavender flowers.
It spreads quickly to form dense thickets, especially near water.

Species: Indigo bush

Robert Vidéki, Doronicum Kft., Bugwood.org

Indigo bush is a thornless shrub that loses its leaves in the winter (deciduous). Stems grow roughly 12 feet tall. Plants form dense thickets.

Species: Indigo bush

Rebekah D. Wallace, University of Georgia, Bugwood.org

Leaves have a central stem with 13–25 leaflets arranged opposite each other along the stem as shown in the photo. The leaflets are one to two inches long, dotted, and hairy.

Species: Indigo bush

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

Indigo bush blooms in May through June. Showy flowers are violet to purple with yellow anthers. They are densely arranged on erect stems.

Species: Indigo bush

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

Indigo bush spreads primarily by seed and also by suckers. It thrives along waterways and floodplains. It also grows in meadows and along forest edges and rights-of-way.

Species: Indigo bush

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

Indigo bush seeds mature in small fruit pods. Each pod contains 1–2 seeds. The pods float in water to new locations.

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Indigo Bush Benefits

Indigo bush flowers produce rich nectar. It is an important food source for bees. Beekeepers market indigo bush honey.
It is a larval food host for many North American butterflies and moths.
It has significance for Native American people in North America. The stems and leaves are used for fiber and medicine.

Indigo Bush Risks

Indigo bush forms dense thickets along riverbanks and riparian zones, canyons, and seeps. So far, it is mainly found in areas along the Columbia River or short distances up tributary streams from the river itself. That could change as the plant population increases.
Indigo bush crowds out native shrubs and trees that provide food for birds, insects, beaver, and deer.
It blocks recreational access to rivers and reservoirs.

Risk Card

Does it cause harm?

Adults & Children

Low

Property

High

Pets

Low

Annoyance

High

Environment

High

Action Highly Recommended

TAKE ACTION?

Don’t allow indigo bush to establish on your property. Remove indigo bush before individual plants can spread by root sprouts or seed.

Do I need to take action?

Yes. Report the plant location. You may be able to get help to determine a plan and act to control indigo bush on your property.
Prevent indigo bush from producing seed pods. The seed pods float on water, which spreads indigo bush to new locations.
Indigo bush plants and seeds are sold at nurseries and online. Don’t buy this invasive species or plant it in your landscape.

What if I do nothing?

If no action is taken, indigo bush will spread quickly to form dense thickets. It dominates an area when left unmanaged.
The longer you wait to act, the more time and effort will be required to control it.

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 Indigo Bush

Early Detection and Rapid Response

Watch for indigo bush on property you manage. Remove it before it becomes a bigger problem.

Physical Removal of Plants and Non-Chemical Options

Indigo bush is difficult to control mechanically. When stems are removed, sprouts emerge from roots.
Pull out single shrubs or repeatedly cut stems and dispose of them.
Cut the stems at the base several times during a growing season for several years. This depletes energy reserves stored in the root system. It also limits seed production.
Use a tractor to remove isolated bushes. Remove as much of the root system as possible.

Herbicides (Weed Killers)

Herbicides effectively control indigo bush when used according to label directions.

Monitoring and Follow-Up

Look for indigo bush on your property every year and act as needed.

Method	Does it work?	Is it safe?	Recommendation
A Physically Remove Plants	Somewhat effective	Low risk	Recommended
B Herbicides Triclopyr, Glyphosate & Imazapyr for Non-Aquatic Areas	Effective	Moderate risk	Use if Necessary
C Herbicides for Aquatic Areas	Effective	Moderate risk	Use if Necessary
D If Using Herbicides, Protect Yourself & Minimize Risks
E Prevent More Indigo Bush

Physically Remove Plants

Non-Chemical Method

Weston Miller, Oregon State University

Physically Remove Plants

Recommended

Pull out single shrubs, or cut the stems at the base several times during a growing season for several years. This depletes energy reserves stored in the root system. It also limits seed production.

Does it work?	Somewhat effective Mechanical control options are limited. Combine mechanical control with herbicides and multi-year monitoring for best results.
How much effort?	Moderate effort Heavy equipment can be used for removal. Stems can be cut repeatedly. These efforts are costly and don’t provide long-term control.
What's the risk?	Low risk
Possible risk of exposure or harm from chemicals	NONE

Look for seedlings, single plants, and small patches of indigo bush and remove them each year. Don’t allow it to get established.
If you have established stands of indigo bush on your property, they will require annual management.

Worker using weed wrench tool to remove a shrub

James H. Miller, USDA Forest Service, Bugwood.org

Manual removal of indigo bush is effective but labor-intensive. Using a Weed Wrench™ or similar tool makes it easier to remove smaller shrubs.

James H. Miller, USDA Forest Service, Bugwood.org

Use a tractor to remove isolated bushes. Remove as much of the root system as possible.

INDIGO BUSH REMOVAL TIPS

Pull out single shrubs, or repeatedly cut stems and dispose of them.
When stems are removed, sprouts emerge from roots. Cut the stems at the base several times during a growing season for several years. This depletes energy reserves stored in the root system. It also limits seed production.
Remove all cut stems from the site. Indigo bush regenerates from stem fragments.
Use a tractor to remove isolated bushes. Remove as much of the root system as possible.

Soil Disturbance and Erosion

Minimize soil disturbance as much as possible when removing indigo bush.
Regrade the soil after digging roots. Apply mulch (when appropriate).
Take steps to prevent erosion as needed.
Replant the area to shade indigo bush seedlings.

Herbicides Triclopyr, Glyphosate & Imazapyr for Non-Aquatic Areas

Chemical Method: Use with caution

Lyon Duong, UF/IFAS

Herbicides Triclopyr, Glyphosate & Imazapyr for Non-Aquatic Areas

Use if Necessary

Herbicide products that contain active ingredients glyphosate, triclopyr, and imazapyr are effective treatments for indigo bush when label directions are followed.

Does it work?	Effective The cut stump method of herbicide application (shown in photo) is the most effective method for established stands of indigo bush. Applying herbicide to foliage doesn’t work as well.
How much effort?	Moderate effort 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 triclopyr, glyphosate, and/or imazapyr, used individually or in a mixture, are effective chemical treatments for indigo bush. 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. Text on the label states “Kills completely — stumps and roots won’t regrow.”
Triclopyr doesn’t injure most grasses. It is a good choice for treating indigo bush that is growing next to desired grasses in lawn, pasture, and meadow areas.

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.
Imazapyr is soil-persistent and may affect adjacent non-target plants whose roots encroach on the sprayed area.

Herbicide Application Tips

Premixed products are available in hardware stores and garden centers.
Apply herbicide to indigo bush in the spring or early summer when it is actively growing, before or after it blooms. Treat indigo bush before seed pods develop to minimize seed production.
Indigo bush may take several months to die following an herbicide application.
Look for indigo bush regrowth and re-treat every year, if needed.

Minimize the potential impact of herbicides to bees and other pollinators. Treat indigo bush plants before they flower. If plants are blossoming when you need to treat them, use the cut-stump or basal bark herbicide application technique. Avoid spraying pollinators directly. For more information, see OSU’s How to Reduce Bee Poisoning from Pesticides.

Gloved hand spraying herbicide with dye on cut stump

Lyon Duong, UF/IFAS

Cut-Stump Application

Cut stems as close to the ground level as possible.
Remove sawdust and debris from the cut.
Apply concentrated herbicide to the area just inside the bark. This area has living tissue (cambium) that will transport the herbicide to the roots.
Apply herbicide as soon as possible after cutting the stem.
For cut-stump applications, triclopyr is more effective during the early summer. Glyphosate is more effective when applied from mid-summer to leaf fall.

Herbicides for Aquatic Areas

Chemical Method: Use with caution

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

Herbicides for Aquatic Areas

Use if Necessary

Indigo bush often grows along waterways. Herbicides used for this situation must be registered for aquatic use.

Does it work?	Effective It takes repeated effort over several years to get rid of a well-established stand of indigo bush.
How much effort?	High effort Treating indigo bush 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 herbicide products that contain glyphosate are effective chemical treatments for indigo bush on or near water.

Herbicide Application Requirements for Aquatic Areas

Herbicides applied over or near a water body must be registered for aquatic use.
Aquatic-use products are rarely sold at plant nurseries or garden centers. They are available through specialty pesticide dealers.
Treating indigo bush near aquatic areas requires specialized skills. This ensures the herbicide is applied effectively. It also protects waterways.

Consider hiring a licensed pesticide applicator to manage indigo bush in aquatic 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 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).