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Johnsongrass

Sorghum halepense

Updated Nov 04, 2022

Make a Positive Identification

Johnsongrass is an invasive, Eurasian perennial (lives many years) grass that grows up to 8 feet tall. It spreads by seeds and creeping rhizomes (roots). Populations are scattered throughout the Pacific Northwest.
It thrives in agricultural and disturbed sites. Such sites include orchards, vineyards, cultivated fields, roadsides, irrigation canals, drainage ditches, and riparian areas.
Johnsongrass quickly forms dense stands that suppress crop growth. It displaces native species in natural areas.

Species: Johnsongrass

Stefan.lefnaer, CC BY-SA 4.0, via Wikimedia Commons

Johnsongrass grows up to 8 feet tall. It thrives in disturbed areas. It is most often found in croplands, rangeland, drainage ditches, roadsides, and riparian areas.

Species: Johnsongrass

Johnsongrass leaf blade with white midrib

"Sorghum halepense leaf4" by Macleay Grass Man is licensed under CC BY 2.0.

Mature grass blades are flat with a prominent white midrib as shown in the photo on the left. Blades are 12–30 inches long and ½ –1 inch wide.

Species: Johnsongrass

Whitebox highlighting Johnsongrass igule

"Sorghum halepense - Johnsongrass" by Matt Lavin is licensed under CC BY-SA 2.0.

Johnsongrass’s round stems stand upright and are hairless and sparsely hairy where the leaf blade meets the stem. A papery flap of material called the ligule grows from where the leaf blade connects to the stem (leaf sheath). Ligule growth is variable. It can be intact and ¼-inch long or hidden, or show as fringe.

Species: Johnsongrass

Johnsongrass flower head against blue sky

Harry Rose from Dungog, Australia, CC BY 2.0, via Wikimedia Commons

Flowers grow in a pyramid- or cone-shaped flower head from late spring to early fall. They range from purple-brown to golden to pale green.

Species: Johnsongrass

Steve Hurst, USDA NRCS PLANTS Database, Bugwood.org

Johnsongrass flower heads form abundant fruits and then seeds that spread to new locations.

Species: Johnsongrass

Steve Dewey, Utah State University, Bugwood.org

Seedlings closely resemble corn seedlings. They are similar to rhizome sprouts.

Species: Johnsongrass

Steve Dewey, Utah State University, Bugwood.org

This perennial grass grows creeping rhizomes (roots) to form a dense clump.

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LOOK-ALIKES: REED CANARYGRASS AND OTHER SORGHUM SPECIES

Species: Reed canarygrass

Michael Shephard, USDA Forest Service, Bugwood.org

Reed canarygrass (Phalaris arundinacea) grows up to 8 feet tall. It grows in agricultural fields, drainage ditches, roadsides, and natural areas.
Reed canarygrass flowers grow in dense spikes. In comparison, johnsongrass flowers grow in pyramid- or cone-shaped flower heads.

How to Get Rid of Reed Canarygrass

Species: Sudangrass

"Nick and sudan grass" by William Moore Farms is licensed under CC BY-ND 2.0.

Milo (Sorghum bicolor) and sudangrass (Sorghum × drummondii) are crop plants. They are both tall growing and are related to johnsongrass.
The photo shows a stand of sudangrass cover crop.
Both crops are annual plants (complete their life cycle in a year) that don’t spread via roots.

Different risks or methods

Milo and Sudangrass usually don’t require control efforts.

Johnsongrass Benefits

Johnsongrass is a destructive weed. It doesn’t have any benefits for people or the environment.

Johnsongrass Risks

Johnsongrass quickly forms dense stands. It crowds out desired vegetation, significantly reducing crop yields.
It also damages irrigation and drainage infrastructure.

Risk Card

Does it cause harm?

Adults & Children

None

Property

High

Pets

Some

Annoyance

High

Environment

Some

Action Highly Recommended

TAKE ACTION

If you have johnsongrass on your property, take action to control it.

Do I need to take action?
Yes. Remove individual plants and small patches. Established patches require several years to control.

What if I do nothing?
Johnsongrass forms dense stands and is difficult to control. The longer you wait to act, the more difficult it will be 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 Johnsongrass

Early Detection & Rapid Response

Watch for reed johnsongrass on property you manage. Remove it before it becomes a bigger problem.

Physical Removal of Plants & Non-chemical Methods

Dig out single plants and small patches to remove the root mass and all of the rhizomes.

Herbicides (Weed Killers)

Herbicides effectively control johnsongrass when used according to the label instructions.

Monitoring & Follow Up

Restore the area by planting native trees and shrubs to shade out johnsongrass. Monitor the area and re-treat as needed.
It takes repeated effort over several years to get rid of a large, established stand of johnsongrass.

Method	Does it work?	Is it safe?	Recommendation
A Physically Removing Plants, Mowing & Disking	Effective	Low risk	Recommended
B Glyphosate and Grass-Selective Herbicides	Effective	Moderate risk	Use if Necessary
C If Using Herbicides, Protect Yourself & Minimize Risks
D PREVENT JOHNSONGRASS

Physically Removing Plants, Mowing & Disking

Non-Chemical Method

Weston Miller, Oregon State University

Physically Removing Plants, Mowing & Disking

Recommended

Dig out small patches with tools. Mowing and tarping are useful methods for johnsongrass, but other methods are necessary to get rid of it.

Does it work?	Effective Requires several years of monitoring and effort. Use preventive measures for best results.
How much effort?	High effort All rhizome fragments must be removed. This is extremely difficult if managing an established stand.
What's the risk?	Low risk
Possible risk of exposure or harm from chemicals	NONE

Dig out young, individual plants and small patches to remove the root mass and all the rhizomes.
Repeated mowing effectively controls johnsongrass spread. However, other control actions, such as herbicides, are required to reduce or eliminate the patch.
Similar to mowing, johnsongrass is sensitive to disking or plowing. Further action is required to get rid of it.

Ohio State Weed Lab , The Ohio State University, Bugwood.org

Physically Removing Plants

Johnsongrass spreads with seeds and rhizomes.
You must remove all of the root fragments (shown in photo) or it will regrow.

kn1, iStock

Mowing

Mowing alone is not recommended to control johnsongrass. It will regrow and bloom following limited mowing.
However, repeated mowing will ensure control if done every few weeks throughout the growing season. This will reduce flower cluster growth.

Tractor with disk attachment cultivating field

freeteo, iStock

Disking

Cultivation with disks or other equipment provides benefits when used with other control activities, but if used alone will spread johnsongrass.
Choose tillage equipment and use clean equipment that eliminates spreading rhizome fragments.

Soil Disturbance and Erosion

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

Glyphosate and Grass-Selective Herbicides

Chemical Method: Use with caution

Chameleonseye, iStock

Glyphosate and Grass-Selective Herbicides

Use if Necessary

Herbicide products that contain active ingredients glyphosate and herbicides that target grasses (grass-selective) are effective treatments for johnsongrass when label directions are followed.

Does it work?	Effective Use preventive measures for best results.
How much effort?	Moderate effort Requires several years of monitoring and treatment.
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.

Herbicide products containing active ingredients glyphosate and and grass-selective herbicides such as fluazifop effectively control quackgrass when label instructions are followed. Look for these chemical names in the “Active Ingredients” section of product labels.

Photo of herbicide label highlighting active ingredient glyphosate

Weston Miller, Oregon State University

The white box on the example label highlights active ingredient glyphosate. Text on the label states “Kills grass and weeds around flowerbeds....”
Glyophosate will damage most plants and grasses. Don’t let the spray contact plants that you want to keep.

Photo of herbicide label highlighting active ingredient fluazifop

Weston Miller, Oregon State University

Grass-selective herbicides such as fluazifop effectively control reed canarygrass.
These products don’t injure desired plants when used as directed on the label instructions. They can be used around ground covers, flower beds, and shrubs (bushes), and trees.
The white box on the example label highlights active ingredient fluazifop. Text on the label states “KILLS WEEDY GRASSES WITHOUT INJURING ORNAMENTAL PLANTS.”

Herbicide Application Tips

Premixed products are available in stores.
Killing rhizomes is critical to eliminating johnsongrass.
Herbicide products applied to the leaves in spring or fall are effective at controlling spread.
Herbicides applied after flowering are more effective at killing rhizomes.
However, the specific timing and application method depends on the herbicide product. Follow the label instructions for best results.
It takes repeated effort over several years to get rid of a well-established stand of Johnsongrass.

Herbicide Application Requirements for Aquatic Areas

Herbicides applied over or near a water body must be registered for aquatic use.
Treating Johnsongrass 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 this weed in aquatic areas. Aquatic-use products are rarely sold at plant nurseries or garden centers. They are available through specialty pesticide dealers.
Aquatic formulas of herbicide products that contain active ingredient glyphosate effectively control johnsongrass when used according to label directions.
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.

If Using Herbicides, Protect Yourself & Minimize Risks

Chemical Method: Use with Caution

SteveOehlenschlager, iStock

Why is it important to ready 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 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.

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.

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).