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How to Kill Johnson Grass: The Definitive Guide

How to Kill Johnson Grass?

Johnson grass can be a pesky weed to get rid of. It is hardy, fast-growing, and difficult to eradicate. However, with the right information and tools, you can successfully kill Johnson grass without too much trouble. In this guide, we will answer some common questions about how to kill Johnson grass and provide tips on how to make the process as easy as possible for you. Let’s get started!

What is Johnson Grass?

Johnson grass (Sorghum halepense) is a perennial grass that is native to the Mediterranean region. It is now found in many parts of the world, including the United States. Johnson grass can grow up to six feet tall and has thick, fibrous roots. The leaves are long and narrow, with a sharp point at the tip.

What is Johnson Grass?

Johnson grass is a problem for farmers because it can reduce crop yields by competing for water, nutrients, and space. In some cases, it can also harbor diseases or pests that can infect other plants. Johnson grass is also a problem for homeowners because it can invade yards and gardens, crowding out other plants.

Plant characteristics

Johnson grass is a fast-growing, perennial grass that can reach up to six feet in height. It has thick, fibrous roots and long, narrow leaves with sharp points at the tips. The flowers are small and green, growing in clusters at the top of the plant. Johnson grass is considered a weed in many parts of the world because it grows rapidly and spreads easily. It can crowd out other plants, including crops, and make it difficult for them to compete for resources.


Johnson grass spreads by rhizomes, or underground stems. When the plant dies back in winter, the rhizomes remain alive and produce new shoots in spring. This makes Johnson grass difficult to control because if you don’t kill the entire plant, it will come back.

Also, because Johnson grass is a grass, it produces seeds. One plant can produce up to 30,000 seeds, which are then spread by wind and water.

If you have Johnson grass on your property, the best thing you can do is dig it up. This is a tedious process, but it’s the only way to be sure you’ve removed all of the rhizomes. You’ll need to dig at least 12 inches deep and 12 inches out from the main plant. Once you’ve dug up the plant, put it in a bag and dispose of it in the trash. Don’t compost it!

Interfertility with other sorghum species

Johnson grass is highly interfertile with other sorghum species. This means that it can cross-pollinate with other sorghum plants, and the resulting offspring are often sterile. The only way to ensure that your Johnson grass plants are not crossing with other sorghum species is to physically remove them from the area.

Interfertility with other sorghum species

If you have Johnson grass in your field, make sure to check the surrounding area for other sorghum plants. If you find any, pull them up and destroy them. This will help prevent your Johnson grass from crossing with other plants and becoming less productive.

In general, Johnson grass is a fairly easy plant to control. However, if you let it go unchecked, it can quickly take over your field.


Johnson grass is often confused with sorghum (Sorghum bicolor), but sorghum does not have the white midrib on its leaves. Take a look at the leaf closely and you’ll see a white line running down the center. That’s your key to identification. Johnson grass also has a fibrous root system, while sorghum has a taproot. The two plants are often found together in areas of disturbed soils, such as roadsides and construction sites.

The plant produces pollen that is wind-borne to other plants, where it fertilizes the ovules and forms seeds. Seeds mature in August or September and fall to the ground to overwinter until the next growing season. Johnson grass is a prolific seed producer, and just a few plants can result in a large infestation the following year.

The best time to control Johnson grass is before it produces seeds, so keep an eye out for flowering plants in late spring and early summer. However, the plant can be controlled at any time during its growing season. Smaller plants are easier to control than larger ones, so don’t wait too long to take action.


The first step is to identify whether Johnson grass is the problem. This can be tricky, as there are many varieties of grass, and they can all look very similar. If in doubt, take a sample of the plant to your local nursery or Cooperative Extension office for identification. Once you’re sure it’s Johnson grass, you can move on to control methods.

Johnson grass is a perennial weed, meaning it comes back year after year from the same root system. That means that simply pulling it up won’t work – the roots will just resprout new plants. You need to dig up the entire root system to get rid of Johnson grass for good.

This task is challenging, but it’s not impossible. The key is to be patient, and to keep at it until the job is done.

How to Get Rid of Johnson Grass

Johnson grass is an incredibly resilient and fast-growing species of grass that can quickly take over your lawn or garden.

How to Get Rid of Johnson Grass

With a little time and effort, you can get rid of this pesky grass for good!

Cultural control

The first step in getting rid is to start with cultural control. This means mowing it regularly so it doesn’t have a chance to flower and produce seeds. You’ll also want to make sure you don’t let the soil around it get too compacted, as this will only make it harder to kill.

If you have a large area of Johnson grass, you may want to consider tilling it under before you start mowing. This will help loosens the soil and make it easier for the roots to be killed off.

Focus on one area at a time and work your way around the property. Be patient, as it may take a few years of consistent effort to finally get rid of all the Johnson grass.

Another cultural control method is to plant competitive grasses around the area where Johnson grass is growing. This will help crowd it out and prevent it from getting the sunlight and nutrients it needs to survive. Fescue and bluegrass are two good options to consider planting.

Also you can to dig up Johnson grass by hand. This takes some time and effort, but it’s worth it if you want to get rid of the plant for good. Start by wetting the soil around the plant so that it’s easier to dig. Then, use a spade or shovel to dig up the roots of the plant. Be careful not to damage the roots of nearby plants. Once you’ve removed the plant, place it in a garbage bag and throw it away.

Johnson grass control with herbicides

There are several herbicides that will kill Johnson grass, but timing of application is important. Postemergence herbicides are most effective when applied to young plants before they produce rhizomes or seeds. Glyphosate is a non-selective herbicide that kills any plant it comes in contact with, so care must be taken to avoid spraying desirable plants. Glyphosate is best applied to Johnson grass when it is actively growing in the spring or fall. Imazapyr and imazaquin are both effective postemergence herbicides for Johnson grass control, but they may damage certain types of trees and shrubs if not used carefully. Consult the labels of these products for specific application instructions and precautions.

Preemergence herbicides can be applied before Johnson grass germinates in the spring, or after it has produced seeds in the fall. Herbicides that contain siduron, imazaquin, or oxadiazon are effective preemergence options for preventing Johnson grass growth. Be sure to follow all label instructions when applying any herbicide product.

Johnson grass control with herbicides

Corn gluten meal

Corn gluten meal is an organic herbicide that’s effective in killing Johnson grass. To use, mix corn gluten meal with water and apply it to the leaves of the plant. Make sure to cover the entire leaf so that the herbicide can be absorbed. Follow these steps until the plant dies. Repeat this procedure every fourteen days until the plant is extirpated.

Soybean and cottonseed oils

Soybean and cottonseed oils are also effective in killing Johnson grass. These oils work by suffocating the plant. Soybean or cottonseed oil should be combined with water and applied to the plant’s leaves.

Adjuvants and cultivation in corn, soybean and cotton

Adjuvants are chemicals that improve the effectiveness of herbicides. You can find adjuvants at most garden stores.

Cultivation is another method you can use to kill Johnson grass. This involves tilling the soil around the plant to expose its roots. Then, simply cut off the roots with a shovel or spade. Be sure to wear gloves and long sleeves when doing this so that you don’t get any of the sap on your skin. Continue until the plant dies by repeating these steps every two weeks.

Alfalfa, birdsfoot trefoil, clovers and vetches

These plants work by smothering the plant and preventing it from getting sunlight. To use, simply plant these plants around the base of the Johnson grass plant. Make sure to water them regularly so that they don’t die. Repeat this process every two weeks until the plant dies.

Grain sorghum

Grain sorghum is an annual grass that can be planted to kill johnson grass. It has a deep root system that will help to compete with the johnson grass for water and nutrients. You can plant grain sorghum in the spring or summer.

Selective herbicide applications for johnson grass control

The most effective herbicide is glyphosate. Glyphosate will kill johnson grass and many other broadleaf and grassy weeds, but will not harm most common lawn grasses. For this reason, it is important to use a glyphosate product that specifically mentions johnson grass on the label.

Glyphosate products are available in both liquid and granular formulations. The granular products are often easier to apply than the liquids, but both types are effective. Glyphosate should be applied to dry foliage and allowed to absorb for at least two hours before rain or irrigation. It is best to wait at least one week after application before mowing the lawn. [1]

Preharvest johnson grass control

Preharvest johnson grass control

Preharvest control in Roundup Ready crops is achieved by applying glyphosate at the full recommended rate plus a nonionic surfactant (NIS) at 0.25% v/v to 0.50% v/v. Glyphosate products that contain NIS do not require an additional surfactant. Glyphosate should be applied to johnsongrass when it is actively growing and before it reaches reproductive maturity, which occurs when flower stalks appear in late summer or early fall. The addition of a crop oil concentrate (COC) or ammonium sulfate (AMS) will improve glyphosate performance on johnsongrass; however, these additives are not necessary if glyphosate plus NIS is used. Glyphosate will kill the johnsongrass plants; however, it will not kill the rhizomes (underground stems) that produce new johnsongrass plants. For this reason, glyphosate should be applied to johnsongrass before it produces flower stalks that release pollen and before seed heads develop and mature. If glyphosate is applied after these reproductive structures have developed, then viable seed can be produced and new johnsongrass plants will result.

The best time to apply is early morning or late evening when temperatures are cooler and wind speeds are low. This allows for better product performance and minimizes potential injury to the crop. Glyphosate should not be applied to Roundup Ready crops during the heat of the day or when wind speeds are high as this can result in crop injury.


What is the best product to kill Johnson grass?

The best product to kill Johnson grass is Roundup. It is a systemic herbicide that will travel through the plant and kill it from the roots up.

Roundup is available in both liquid and granular form. The liquid form is easier to apply, but the granular form lasts longer. Whichever form you choose, be sure to follow the instructions on the label carefully. [2]

Another option is to use an herbicide with glyphosate as the active ingredient. Glyphosate kills Johnson grass from the roots up, but it may take a little longer than Roundup.

How do you stop Johnson grass?

The best way to stop Johnson grass is to remove the root system. This can be done by physically digging up the plant or by using a herbicide. Johnson grass may be destroyed with glyphosate, which is a popular herbicide. Be sure to follow the instructions on the glyphosate label and apply it when the grass is actively growing.

If you have Johnson grass in your lawn, you may be able to control it by mowing high and frequently. This will prevent the grass from producing seed heads and spreading. You may also want to consider overseeding your lawn with a more desirable species of grass.

Johnson grass can be a difficult plant to control, but with persistence and patience, it can be done!

How do you kill Johnson grass in St Augustine?

The best way to kill Johnson grass in St Augustine is to use a herbicide with the active ingredient glyphosate. Glyphosate will kill Johnson grass without harming your St Augustine lawn. You can find glyphosate herbicides at your local garden center or home improvement store.

To apply glyphosate, first cut the Johnson grass down to ground level using a string trimmer or lawn mower. Then, mix the glyphosate herbicide according to the manufacturer’s instructions and apply it to the leaves of the Johnson grass plants. Be sure to follow all label directions when using any pesticide. [3]

If you have a large area of Johnson grass, you may need to reapply the glyphosate herbicide every few weeks until all the plants are dead.

How do I get rid of Johnson grass in Bermuda?

One way is to physically remove it by hand pulling or digging it up. Another way is to use an herbicide, such as glyphosate. Glyphosate will kill the roots of the plant, so it will not regrow. You can also use Pendulum 3.3 EC. This herbicide will also kill the roots of Johnson grass, but it has a longer residual effect, so it will continue to kill new growth for up to six months. [4]

The best time to apply an herbicide is early morning or late evening when temperatures are cooler and wind speeds are low.

Be sure to follow the instructions on the label when using any herbicide. You should also take care not to let the herbicide come into contact with any desirable plants, as it will kill them as well.

Once you have killed the Johnson grass, you can then replant desired vegetation in its place. Be sure to choose plants that are appropriate for the growing conditions in your area.

Useful Video: How to Kill Johnson Grass


Johnson grass is a pesky weed that can be difficult to get rid of. However, with the right tools and methods, it is possible to kill this weed and take back your yard or garden. With a little patience and persistence, you will be able to rid your property of this nuisance weed once and for all. Thanks for reading!


  1. https://extension.missouri.edu/publications/g4872
  2. https://mdc.mo.gov/trees-plants/invasive-plants/johnson-grass-control
  3. https://tylerpaper.com/first-make-sure-johnsongrass-in-st-augustine-lawn-is-really-johnsongrass/article_0163e917-d0fc-546e-a023-0c15a8d74ed8.html
  4. https://www.domyown.com/what-herbicide-kills-johnson-grass-without-harming-my-bermuda-qa-11333.html