- How to Kill Johnson Grass in a Hay Field
- Controlling Johnson Grass – How To Kill Johnson Grass
- How to Get Rid of Johnson Grass
- Recommended Johnson Grass Herbicides
- Johnson Grass Control
- Effects on Natural Communities
- Control Recommendations
- Recommended practices in natural communities of high quality
- Recommended practices on lands other than high-quality natural areas
- Failed or Ineffective Practices
- Don’t Overlook Johnsongrass in Your Pasture
- Johnsongrass Control
- Plant characteristics
- Interfertility with other sorghum species
- Cultural control
- Johnsongrass control with herbicides
- Selective herbicide applications for johnsongrass control
- Preharvest johnsongrass control
- Johnsongrass Control in Pastures, Roadsides, and Noncropland Areas
- Johnsongrass control
- Selective herbicides for control in roadsides and noncrop areas
- Timing herbicide applications
- Getting Rid of Johnson Grass
- Grassy Weeds – Dallisgrass, Johnsongrass, Fescue Clumps, et al
How to Kill Johnson Grass in a Hay Field
grass image by Thomas Quinlan from <a href=’http://www.fotolia.com’>Fotolia.com</a>
Johnson grass self propagates through seeds and large rooting rhizomes. This troublesome plant will quickly spread through a hayfield when left uncontrolled. Several states have legislated requirements for control of this noxious weed. The best defense against Johnson grass infestation is to begin a control program as soon as the plant is identified. Often once the plant becomes firmly established, it becomes difficult to kill in a hayfield without damaging the main hay crop.
Keep the Johnson grass plants mowed as low to the ground as possible. This will weaken the plant and keep the stalks from producing seed heads. In a large hayfield that may entail using a hand held sickle or scythe blade to keep the plants in check prior to hay harvest. Remove the tops of the plants from the field if there are any signs of seed head development.
Mix the herbicide glyphosate according to label directions. Pour the herbicide into a rope wick applicator.
Walk through the hayfield and wipe each blade of the Johnson grass you come across. The tip of the rope wick applicator will keep the herbicide from coming into contact with the hay field crop plants.
Cultivate the rhizomes of the Johnson grass in late fall to early winter with the disc cultivator. Breaking up the plants and exposing the rhizomes to freezing temperatures will kill the root system. This may not be possible with established hay fields and should only be done when the Johnson grass has taken over the field. In cases such as these, the field will have to be re-planted for a new hay crop.
Controlling Johnson Grass – How To Kill Johnson Grass
Johnson grass (Sorghum halepense) has plagued farmers since its introduction as a forage crop. This invasive and noxious weed has gotten so out of control that many states require landowners to kill Johnson grass. If you are a landowner bothered by a troublesome invasion of the perennial weed, you probably just want to get rid of Johnson grass.
How to Get Rid of Johnson Grass
As with most invasive weeds and grasses, using multiple strategies usually works best for Johnson grass control. This means that you may use a Johnson grass herbicide program along with other kinds of Johnson grass control methods. This is fitting, as Johnson grass reproduces and invades crop areas in two ways, spreading both by seed and rhizomes to overtake farmland and other areas of your property. The rhizomes of Johnson grass are identified by thick cream-colored rhizomes, covered with orange scales.
Herbicides alone are usually not enough to be an effective Johnson grass killer. When combined with cultural practices that prevent the spread of rhizomes and seeds, a Johnson grass herbicide program, with repeated applications, may provide enough Johnson grass control to eliminate it.
Tilling the soil in fall following the harvest and followed with an herbicide is a good start to kill Johnson grass. Rhizomes and seed heads brought to the surface by tilling may be destroyed in this manner.
The seeds of Johnson grass that are missed during the applications can remain viable for as long as 10 years so it is best to prevent the seeds from being spread in the first place. Take steps to prevent the spread of seeds and rhizomes to areas that are not infested. Digging clumps of Johnson grass in the yard or small garden is a start. Dispose of the clumps where they cannot reseed or spread. It is best to do this before the grass goes to seed, to further prevent the spread of the seeds.
When Johnson grass grows near the lawn, keep the turf thick and healthy to discourage the invasion of Johnson grass. Take a soil test and apply recommended amendments to keep the grass growing. Reseed thin areas of the lawn and mow at the proper height for your variety of grass to keep it healthy and competitive against the Johnson grass.
Recommended Johnson Grass Herbicides
Successful Johnson grass control may include the use of Johnson grass herbicide. Post emergence products may be effective in outlying areas of the property. Glyphosate may work as Johnson grass control near the lawn, but can damage surrounding turf.
Note: Chemical control should only be used as a last resort, as organic approaches are more environmentally friendly.
Johnson Grass Control
Learn more about Johnson Grass
Effects on Natural Communities
Johnson grass invades riverbank communities and disturbed sites, particularly fallow fields and forest edges, where it crowds out native species and slows succession. It quickly dominates the herbaceous flora, reduces plant diversity, and is unsightly to observers. This grass is a serious potential threat in many old fields where succession to forest communities is desired.
To eradicate Johnson grass, control measures must be thorough. Various cultural practices and chemical herbicides will effectively control germinating seed, seedlings, and established plants. Objectives of a good control program include:
- Prevent production and spread of seed
- Destroy seedlings before rhizomes are formed
- Weaken and kill existing rhizomes
- Control new infestations as they appear
Recommended practices in natural communities of high quality
Initial effort in areas of heavy infestation
Johnson grass does not infest areas of high natural quality heavily except for the naturally disturbed environment such as along river banks where it is difficult to control selectively. Seed panicles should be cut and removed from the area where practical. Dense patches can be controlled by spraying the foliage with 2 percent Roundup (a formulation of glyphosate). Best results are obtained when glyphosate is applied to plants that are 18 inches tall to early flowering stage.
During this period the herbicide will be most effectively translocated to the roots and rhizomes. Care should be taken to avoid contacting non-target plants, since Roundup is a nonselective herbicide. Do not spray so heavily that herbicide drips off the target species. The herbicide should be applied while backing away from the area to avoid walking through wet herbicide. By law, herbicides may only be applied as per label instructions.
Effort in areas of light infestation
Clumps and individual plants may be hand pulled during June, just after a rain when the ground is soft. All plant parts should be removed from the area. Broken stems and roots left in the ground should be dug up if only a small area is involved. It is more effective to spot-treat the individual plants with herbicide than to pull them, and large clumps can be sprayed with 2 percent Roundup using a hand sprayer or backpack sprayer. Herbicide treatment may need to be repeated for several years to ensure good control.
Preferred treatment is hand pulling of individual plants immediately upon discovery. All plant parts, including rhizomes, must be removed. It may be necessary to hand pull a population several times to obtain control. Surrounding seed sources should be eliminated where possible to prevent continual re-invasion.
Recommended practices on lands other than high-quality natural areas
Repeated and close mowing kills Johnson grass seedlings, prevents seed production, and reduces rhizome growth and regrowth of shoots. Sites may be tilled where it is practical (e.g. abandoned cropland) and the exposed roots left to winter kill. Repeated tillage (e.g. six times at two-week intervals during the growing season) prevents rhizome development and reduces Johnson grass populations. Limited early season tillage, however, encourages rhizome growth by spreading pieces of the rhizomes. In a monoculture, livestock may be used to eliminate the Johnson grass by grazing. Spraying 2 percent Roundup on foliage using a tractor and power sprayer provides effective control.
Cutting and removal of seed heads during early July and then spot application of 2 percent Roundup to the foliage usually will be effective if continued for three to four years.
Preferred treatment is the same as given above for high-quality areas. Another treatment is spot application of 2 percent Roundup to eliminate invading individuals the first year and to eliminate all surrounding seed sources.
Failed or Ineffective Practices
The following practices should be avoided:
- Hand control: too slow and not practical in large areas where infestations are heavy. Rhizomes break easily and are often left in the ground. Large mature plants are almost impossible to pull by hand.
- Mowing: usually does not kill or eliminate established plants.
- Fire: more research needed. Spring burns may encourage regrowth.
- Herbicides: single applications seldom eliminate the species from an area.
- Tillage: not practical in many places because of terrain and erosion hazard. It seldom is effective by itself and allows other weedy species to invade. It may also destroy native species present.
- Grazing: Grazing increases the potential for introducing other exotic plants. Livestock trample the soil and damage other species.
- Manipulation of water levels: Johnson grass does not typically occur in areas where water level manipulation is practical.
- Biological controls: livestock grazing may reduce plant vigor, but has negative impacts (e.g., excessive trampling, damage to other species, soil compaction) associated with it. No other biological controls are known that are feasible in natural areas.
Don’t Overlook Johnsongrass in Your Pasture
Livestock producers in the southern Great Plains should not overlook johnsongrass in their pastures. For one thing, under certain conditions it can kill your cattle. Another reason not to overlook johnsongrass is that it is excellent forage – if you can get over the fact that it can kill your cattle!
Positive aspects of johnsongrass
As far as nutritive value is concerned, johnsongrass is tough to beat. One study conducted at the Noble Research Institute from the summer of 1999 to the fall of 2001 showed that the quality, expressed as percent crude protein (% CP), and digestibility, expressed as percent total digestible nutrients (% TDN), of johnsongrass is as good as any of the forages tested (Figure 1). In this study, bermudagrass was neck and neck with johnsongrass in terms of % CP and % TDN. The bermudagrass was a managed stand and was fertilized with 50 to 100 pounds per acre of actual nitrogen. The johnsongrass was unfertilized and unmanaged.
In another Noble Research Institute study that was initiated in the summer of 2007 and is ongoing in 2008, the palatability of several warm-season grasses is being evaluated by forage connoisseurs – yearling steers. In the study, three yearling steers have access to plots containing pure stands of 14 different warm-season perennial grasses (both native and introduced). We count the bites of each steer during their morning grazing to determine their preference for a particular grass or grasses.
After one year of data collection consisting of two grazing cycles conducted during the summer of 2007, johnsongrass came out near the top in this study. Alamo switchgrass was the only other grass in the study that had more bites taken of it than johnsongrass in year one (9,262 versus 6,062, respectively). Preliminary data from the first grazing cycle in 2008 show that johnsongrass is the second most preferred grass in the study this year – second to bermudagrass (5,084 vs. 4,625, respectively). A testament to the preference for johnsongrass by livestock can be seen while driving down the road; pastures that are continually grazed generally won’t have any johnsongrass, but you will see it all along the roadside – out of reach of the fenced-in cattle.
Negative aspects of johnsongrass
Johnsongrass is on the noxious weed list in several U.S. states (including Oklahoma) and has even made the list of the 10 most noxious weeds in the world. Johnsongrass can accumulate nitrates during the summer if exposed to several dry, cloudy days in a row. It can also produce prussic acid (hydrogen cyanide) after stressful conditions such as drought, freezing weather or exposure to a herbicide that kills grasses. If your johnsongrass is subjected to any of these conditions, keep cattle away for about a week to allow the prussic acid to dissipate.
For more information on nitrate and prussic acid poisoning, and testing plants for these compounds, please see the following two articles by Clay Wright in the Ag News and Views archives:
- Drought-Induced Poisonings are Dangerous to Livestock (August 1998); and
- Rethinking Nitrate and Prussic Acid “Quick” Tests (September 2005).
Bill Johnson, Andy Kendig, Reid Smeda and Fred Fishel
Department of Agronomy
Johnsongrass (Sorghum halepense) is a troublesome perennial grass weed that reduces yields in corn, grain sorghum, soybean, cotton and leguminous forages. Originally introduced into the United States as a forage crop, it is now an agricultural pest in most states south of the 42nd parallel. Dense johnsongrass infestations severely limited corn production until the relatively recent introduction of Accent and Beacon herbicides. Several states have legislation requiring eradication or control programs. Johnsongrass is listed as a noxious weed by the Missouri Department of Agriculture, which requires that landowners take steps toward controlling and eradicating the weed on all property owned or under their control.
Growers now have numerous tools to manage this weed. As with most other weeds, the key is to implement multiple control strategies when johnsongrass is first observed and not wait until it is firmly established.
Mature johnsongrass stands 6 to 8 feet tall.
Johnsongrass seed head.
Johnsongrass has a large, jagged-edged, membranous ligule.
Rhizomes of johnsongrass are covered with orange scales.
Johnsongrass is well adapted to compete with crop plants and to spread to new areas. An upright perennial, it often grows 6 to 8 feet tall (Figure 1). It has wide leaves with thickened whitish midribs; its panicles (seed heads) are open (Figure 2), and the many branches support thousands of spikelets from which seeds are readily shattered. A key identifying characteristic of the vegetative stage is its relatively large, jagged-edged, membranous ligule (Figure 3). Shattercane can easily be confused with johnsongrass. The most obvious difference is that since shattercane is an annual grass, it does not produce rhizomes. The leaf blade of shattercane, as much as 3 inches wide, is usually much wider than the 0.8-inch-wide leaf blade of johnsongrass. In addition to a typical fibrous root system, johnsongrass produces thick cream-colored rhizomes, covered with orange scales (Figure 4).
During 1992 various biotypes of johnsongrass in Mississippi were reported to exhibit resistance to Fusilade DX applied at labeled rates. Resistance appeared in fields that had been treated with Fusilade and Poast Plus in at least eight of the previous 10 years. Since that time, at least five counties in Mississippi have johnsongrass populations confirmed resistant to Fusilade, and there are recent reports of resistant johnsongrass in Kentucky. Commonly, resistant populations of johnsongrass are not sensitive to Fusilade DX or Assure II, no matter what rate is applied. Elevated tolerance to Poast/Poast Plus has also been noted, but rates three- to fivefold higher than recommended normally are effective. Field use rates of Select, another selective grass herbicide, are effective in controlling resistant johnsongrass.
Its ability to produce seed and rhizomes and spread to uninfested areas contributes to making johnsongrass a menacing weed. Rhizomes are extensive and are produced in the top 10 inches of soil but have been found at depths of 5 feet. Johnsongrass readily reproduces from rhizomes and seed; seedling plants can initiate rhizomes as few as 19 days following emergence.
A single plant may produce more than 80,000 seeds in a single growing season, and 275 feet of rhizomes. Seeds shatter easily and fall to the ground beneath plants that produce them. Instead of germinating uniformly, seeds can remain dormant and produce plants over several years. Johnsongrass seed can remain viable in the soil for more than 10 years.
Johnsongrass generally grows in fertile bottomlands along creek and river banks and in upland fields. Irrigation ditch banks are also overgrown with johnsongrass, and seed is carried by the water. In a new location, johnsongrass spreads rapidly and soon becomes a serious problem. Tillage equipment can spread the rhizomes, and birds spread the seed.
Agricultural seed, hay and various livestock feeds sometimes become contaminated with johnsongrass seed. In the past, watermelons shipped from the South were often bedded in johnsongrass hay, which was swept out at various dropoff points and contributed to its spread.
Interfertility with other sorghum species
Plant breeders, seed dealers and growers often observe off-type plants or “rogues” of hybrid grain sorghum. Common rogues are the tall outcrosses to sudangrass, johnsongrass or other sorghum types. Sorghum outcrosses with johnsongrass as the male parent often have rhizomes resembling those of johnsongrass. Johnsongrass-grain sorghum hybrids can become a significant weed threat.
Preventing johnsongrass from becoming established in new areas is the best available control method, because the weed spreads in so many ways. Because johnsongrass is a perennial weed, single cultural control measures or herbicide applications rarely provide adequate control.
Johnsongrass control programs should
- Prevent spread of rhizomes from infested to uninfested areas.
- Kill or weaken established plants and their underground rhizome system.
- Control seedlings originating from shattered seed.
- Prevent production of seed and its spread to new areas.
- Use fall tillage to bring rhizomes to soil surface, where they may be killed by winter conditions.
These objectives are closely related and are equally important to the success or failure of a control program. In limited infestations, it is possible and desirable to use herbicides to kill the weed and prevent seed production. The critical time to kill johnsongrass is while the weed is becoming established and before it has spread over the entire field. For sites with established infestations, a fall application of Roundup or Touchdown will kill emerged tissue and often developing rhizomes.
Growing early-maturing crops, plowing immediately after harvest, and tilling as needed are common methods to break up rhizomes and weaken johnsongrass stands in cultivated areas. Johnsongrass responds to tillage like most tough perennial weeds. Intensive tillage will suppress rhizome johnsongrass. Moderate tillage will break and spread rhizomes and allow johnsongrass to thrive. Johnsongrass will spread relatively slowly in true no-till regimes; however, given enough time, infestations may still become severe. Severe infestations often result in pastures converted to row crops. Uncontrolled johnsongrass in fence rows and ditch banks is a common source of johnsongrass seed as well as vegetative encroachment into fields. Spot sprays on fences and ditch banks can eliminate these sources of seeds and rhizomes.
Alfalfa competes well with johnsongrass for a limited time but will eventually weaken. Repeated mowing of an alfalfa-johnsongrass mixture will prevent johnsongrass from producing seed and will inhibit rhizome development. Intensive grazing and mowing can be used to reduce a stand of johnsongrass. If grazed or mowed closely for at least two years, the plants become weak and stunted and the rhizomes become concentrated near the soil surface. Plowing in late fall exposes the rhizomes to low winter temperatures and reduces the stand considerably. For infested areas that cannot be tilled or sprayed, intensive grazing or mowing is probably the best control.
Johnsongrass control with herbicides
To reduce johnsongrass infestations with herbicides, it will be necessary to use an integrated approach consisting of soil-applied herbicides, postemergence herbicides, crop rotation and tillage. Weedy plants such as johnsongrass adapt quickly to a cultural system that does not change from year to year. An example of this type of system is continuous soybean production such as occurs in many river and creek bottoms. Crop rotation is important to disrupt the physical environment that johnsongrass and many other weeds live in and will help to minimize seed and rhizome production. Herbicide rotation is important to minimize selection pressure for herbicide-resistant biotypes.
The programs mentioned below are designed to control other weeds in addition to johnsongrass. However, these programs are designed for fields where johnsongrass is not adequately controlled by current methods. For control methods to be effective, growers must be diligent and apply control techniques as often as necessary.
In no-till corn production, any herbicide that has postemergence grass activity will provide some control of seedling johnsongrass. In conventional-till corn production, Eradicane or another product containing EPTC (Eradicane) can be applied as a preplant incorporated treatment. Rhizomes should be cut up into small pieces using several diskings before treatment. Incorporate Eradicane immediately after application to minimize volatility losses. However, the burndown or preplant incorporated applications will not provide adequate season-long control and additional control measures will be needed.
Postemergence herbicides for johnsongrass control in corn include Accent, Beacon, Poast HC and Roundup Ultra. The initial application of Accent or Beacon should be applied to 4- to 10-inch-tall seedling johnsongrass and 8- to 14-inch-tall rhizome johnsongrass. If regrowth occurs, a second application can be made when johnsongrass regrowth is 8 to 14 inches tall. Accent can be applied as a broadcast treatment on corn until it is 24 inches tall. Accent applications can be made to 24- to 36-inch corn by using drop nozzles. Beacon can be applied as a broadcast spray to corn that is between 4 and 20 inches tall. Do not apply Accent or Beacon to corn that has been treated with Counter insecticide. Consult the label for restrictions with other organophosphate insecticides and postemergence herbicides.
In SR (sethoxydim-resistant or Poast-tolerant) corn, Poast Plus or Poast HC should be applied initially to 10- to 25-inch johnsongrass. If regrowth occurs, a sequential treatment can be applied to 12-inch johnsongrass regrowth. There are no insecticide restrictions and Poast HC can be applied until corn begins to shed pollen.
When Roundup-Ready corn has received full federal approval, Roundup Ultra can be applied to johnsongrass up to 24 inches tall. If regrowth occurs, a sequential treatment can be applied to 12-inch johnsongrass regrowth. Consult the label for stage of growth and insecticide restrictions.
Soybean and cotton
In no-till soybean or cotton production, as in corn production, any herbicide that has postemergence grass activity will provide some control of seedling johnsongrass. In conventional-till soybean or cotton production, Treflan and Prowl can be applied preplant incorporated and will provide some control of seedling johnsongrass. When incorporating these herbicides, set the implement to run 4 inches deep and make two passes over the treated area to ensure adequate mixing of the herbicide with the soil. However, as in corn production, the burndown or preplant incorporated applications will not provide adequate season-long control, and additional control measures will be needed.
Postemergence herbicides for johnsongrass control in soybean and cotton include Assure II, Bugle, Fusilade DX, Fusion, Poast Plus/Rezult G/Conclude G, and Select in regular, non-herbicide-tolerant soybean or cotton. All of these herbicides provide acceptable control, although Assure II, Fusilade and Select are the preferred herbicides for johnsongrass. Roundup Ultra can be used in Roundup-Ready soybean and cotton. In dense infestations, single applications of any of these herbicides will provide incomplete control. Better control is obtained with split applications. It is recommended that the lower herbicide rates be used on seedling johnsongrass that is less than 10 inches tall. The higher rates are recommended for use on rhizome johnsongrass taller than 10 inches. The recommended approach is to target johnsongrass that is 10 to 18 inches tall. Smaller johnsongrass has little leaf area and consequently absorbs limited amounts of herbicide for complete rhizome control. Regrowth after the first postemergence application indicates that there is a significant amount of rhizome johnsongrass present in the field, and a second postemergence application will be needed. To control regrowth, apply the higher rate of a postemergence herbicide to regrowth that is 6 to 12 inches tall. For regrowth applications, it is a good idea to use a different herbicide than that used for the initial application to avoid selection of herbicide-resistant johnsongrass biotypes.
Adjuvants and cultivation in corn, soybean and cotton
Consult the manufacturer’s label for the appropriate adjuvant for postemergence herbicides. Allow seven days after postemergence herbicide applications before any cultivation is practiced. Cultivation too soon after herbicide applications will reduce johnsongrass control as stems and rhizomes are broken before the herbicide can be translocated. Cultivation seven to 10 days after herbicide applications, after the herbicide has translocated, will further weaken the herbicide-injured rhizomes and increase johnsongrass control.
Alfalfa, birdsfoot trefoil, clovers
A preplant incorporated treatment of Balan can be used for control of seedling johnsongrass and other annual grasses in alfalfa. Rhizome johnsongrass will not be adequately controlled with Balan alone. Balan must be incorporated within four hours after application. Variable weed control may result if incorporation is delayed more than eight hours.
Postemergence herbicides include Poast/Poast Plus and Select. These herbicides can be used on new or established seedings and can also be applied when alfalfa is either dormant or nondormant. Apply Poast, Poast Plus or Select to 10- to 25-inch-tall johnsongrass. If regrowth occurs, sequential applications can be made with similar rates to 12-inch johnsongrass regrowth. Consult the label for the appropriate adjuvant for the postemergence herbicides.
Because johnsongrass is closely related to other plants in the sorghum family, including grain sorghum (Sorghum bicolor), current herbicides that control johnsongrass also control or kill grain sorghum. The best management practice for johnsongrass control in grain sorghum will be to grow an alternative crop that has more available registered herbicides.
Selective herbicide applications for johnsongrass control
Selective application equipment can provide economical johnsongrass control in any of the above-listed crops. Typical johnsongrass infestations are distributed unevenly across the field. Chemical costs can be reduced by using a ropewick applicator or by spot spraying the infested areas. In a ropewick applicator, mix 1 part Roundup or Touchdown with 2 parts water. Run the ropewick applicator in two directions across the field so the johnsongrass is wiped or wicked on both sides. The ropewick should be safely run above the crop canopy to avoid contact with crop foliage. Some dripping and crop injury is inevitable; therefore, it is best to use a commercially available ropewick bar designed to minimize dripping.
Spot spraying can also be an economical johnsongrass management tool. In soybean and cotton, the selective grass herbicides mentioned earlier may be mixed with water in a 1 to 2 percent solution and spot sprayed with hand wand, ATV-mounted sprayers, or tractor-mounted sprayers. Roundup or Touchdown spot sprays can also be used but will cause injury or death to crops that are not tolerant of glyphosate herbicides (Roundup or Touchdown).
Preharvest johnsongrass control
Johnsongrass control before harvest will help to reduce rhizome and seed production for subsequent rotational crops. Roundup is labeled for application to mature corn, cotton, grain sorghum, soybean, and wheat. Double-crop soybean may particularly benefit if johnsongrass is sprayed in the preceding wheat crop. Roundup may be applied to standing soybean that has lost all green color in the pods as long as the crop is not being grown for seed. Roundup may be applied to corn at 35 percent grain moisture or less, to cotton when 60 percent of the bolls are open, to grain sorghum at 30 percent moisture or less, and to wheat after the hard-dough stage.
Soybean and wheat should not be harvested for seven to 10 days after application to allow herbicide translocation. These applications may be of limited utility in soybean and cotton, as the application time is typically close to frost. Unless herbicide applications are made at least seven to 10 days before frost, insufficient translocation will occur and the applications will not be effective.
Johnsongrass Control in Pastures, Roadsides, and Noncropland Areas
Bulletin 1513 View PDF picture_as_pdf
Johnsongrass (Sorghum halepense) is a warm-season perennial weed in pastures and roadsides throughout central and northern Georgia. It germinates from seed in spring after overwintering in the soil, but it primarily emerges from dormant rhizomes in areas with a long-term history of infestations. Rhizomes are belowground stems that produce daughter plants and storage reserves for new growth in spring. The persistence of Johnsongrass is primarily associated with extensive rhizome growth that enables populations to spread laterally and dominate areas by preventing desirable speciesfrom flourishing. Johnsongrass may reach heights of 8 to 10 feet, which helps limit the growth of lower growing grasses in mixed stands (Figure 1). It also produces several allelopathic compounds that can be released from the roots and foliage and are toxic to other plants.
Several characteristics of Johnsongrass canhelp with species identification. Johnsongrasshas erect stems and long leaves with a white midvein and thick midrib (Figure 2). The ligule (outgrowth where leaf and leafstalk meet) of Johnsongrass is a prominent membrane with a fringe of hair (trichomes, Figure 3). The inflorescence (the whole flowering head, including stems, stalks, and flowers) is an open panicle, with numerous whorled branches 6 to 20inches in length. Johnsongrass has fibrous rootsand forms from thick rhizomes (Figure 4). The foliage of Johnsongrass can produce cyanogenic compounds (like cyanide and prussic acid) when plants are stressed from cold and drought.
Figure 1. Johnsongrass growth in a Bermudagrass-planted roadside.Figure 2. Johnsongrass leaf.Figure 3. Johnsongrass ligule.Figure 4. Johnsongrass rhizome.
Regular mowing of Johnsongrass may deplete carbohydrate reserves in rhizomes over time and help limit the spread of infestations, and infrequent mowing can help Johnsongrass spread. It often has rapid regrowth during summer months that may warrant monthly mowing to control shoot development. Preemergence herbicides used for grassy weed control, such as the dinitroanilines, may control Johnsongrass establishment from seed but do not control Johnsongrass emergence from rhizomes. Unfortunately, controlling annual grassy weeds with preemergence herbicides may release Johnsongrass, as competition from other species has been reduced by these applications.
Selective herbicides for control in pastures and hayfields. Outrider (sulfosulfuron) is an acetolactate synthase (ALS)-inhibiting herbicide that may be applied from 0.75 to 2 ounces/acre in bermudagrass and bahiagrass for Johnsongrass control (Table 1). Pastora (nicosulfuron + metsulfuron) at 1.25 ounces/acre and Impose (imazapic) at 4 ounces/acre may also control Johnsongrass in bermudagrass pastures but are more injurious tobermudagrass than Outrider. These herbicides should be applied with a nonionic surfactant at 0.25% volume/volume. Applications three weeks after a mowing or prior to plants reaching the seedhead stage can be criticalto optimize efficacy for control. There are no grazing restrictions for Pastora or Outrider. Growers should delay harvesting hay for two to three weeks after treatments to provide these herbicides sufficient time for movement in the Johnsongrass, thus maximizing control.
|WSSA Groupa||Herbicide||Efficacyb||Labeled species||Grazing Restriction (days after treatment)||Harvest Restriction (days after treatment)||Labeled Rate (product/acre)|
(Select Max, others)
|E||alfalfa, perennial peanut||15 days||15 days||see label|
|E||alfalfa||7 days||14 days||see label|
|F||alfalfa||20 days||20 days||4 to 6 fl oz|
|F-G||Bermudagrass, perennial peanut||see label||7 days||4 to 8 oz|
(Pursuit 70DG, 2EC)
|G||alfalfa||30 days||30 days||
1.1 to 2.2 oz
3 to 6 fl oz
nicosulfron + metsulfuron
|G||bermudagrass||0 days||0 days||1 to 1.5 oz|
|E||behiagrass, Bermudagrass||0 days||14 days||0.75 to 2 oz|
(Roundup, Accord, others)
|E||bermudagrass||see label||see label||see label|
bExcellent (E) = 90 to 100% control, Good (G) = 80 to 89% control, Fair (F) = 70 to 79% control.
The ACCase-inhibitors (Group 1 herbicides), clethodim (Select, others) and sethoxydim (Poast, others), may be used to control Johnsongrass in legumes. These herbicides are sold under several trade names and formulations. Check the labels to determine if an adjuvant is required for the specific product formulation. Do not make broadcast applications of these herbicides in fields with desirable grasses mixed with legumes or severe standloss could occur. Raptor (imazamox) and Pursuit (imazethapyr) are labeled for alfalfa with fair activity for controlling Johnsongrass early after emergence. Impose (imazapic) at 4 ounces/acre may also be used inperennial peanut hayfields for controlling seedling plants or for temporary suppression of mature Johnsongrass. There are no selective herbicides for Johnsongrass control in tall fescue. For control in tall fescue, spot-treatglyphosate in a 5% solution or apply using a wick-bar for control, using at least a 41% glyphosate concentrate tomake these treatment solutions.
Selective herbicides for control in roadsides and noncrop areas
Monosodium methyl arsonate (MSMA) is an organic arsenic-based herbicide that may be used to control or suppress Johnsongrass in bermudagrass and tall fescue roadsides (Table 2). However, current buffer restrictions in proximity to water bodies and limitations on the number of treatments permitted in a year can restrict the potentialuse of MSMA in many areas. Sulfonylurea herbicides, such as Outrider (sulfosulfuron) and Derigo (thiencarbazone+ foramsulfuron + iodosulfuron), control Johnsongrass in bermudagrass and bahiagrass roadsides, but cannot be applied to tall fescue. Pastora (nicosulfuron + metsulfuron) and Impose (imazapic) are ALS-inhibiting herbicides that may only be used in bermudagrass due to injury potential to bahiagrass and tall fescue.
|WSSA Groupa||Herbicide||Efficacyb||Labeled Species||
|E||9 to 24 fl oz|
|F-G||bermudagrass||4 to 8 oz|
nicosulfuron + metsulfuron
|G||bermudagrass||1 to 1.5 oz|
|E||bahiagrass, bermudagrass||1.5 to 2.5 oz|
(Roundup, Accord, others)
|G-E||bermudagrass, tall fescue||42 oz|
bExcellent (E) = 90 to 100% control, Good (G) = 80 to 89% control, Fair (F) = 70 to 79% control.
Arsenal (imazapyr) is a Group 2 herbicide that can be selectively applied to bermudagrass at 8 ounces/acre alone or with low rates of glyphosate for Johnsongrass control. High rates of Arsenal have limited selectivity and may be used for weed control along fence lines or other areas for total vegetation control. Group 2 herbicides are systematically translocated throughout the Johnsongrass plant, unlike MSMA, which is immobile. The mobility of these herbicides to belowground rhizomes enhances the long-term control of perennial populations compared to contact herbicides like MSMA.
The acetyl-CoA carboxylase (ACCase) inhibitors clethodim and sethoxydim have limited use in grassy roadsides. However, these chemistries may control Johnsongrass in areas where injury to roadside grasses is tolerable, such as fence lines, industrial areas, or in certain roadside ornamental plantings. See the labels forspecific instructions on adjuvant recommendations and other uses in noncrop areas.
Timing herbicide applications
Fall applications of herbicides are generally more effective than spring treatments for long-term Johnsongrass control. Johnsongrass begins allocating carbohydrates from leaves to rhizomes in fall, which enhances the movement of herbicides in this source-to-sink pattern. Conversely, spring treatments of postemergence herbicides can provide temporary control of Johnsongrass leaves, but rapid regrowth from rhizomes often occurs. While spring treatments can help release desirable species from competition, restricted herbicide translocation to rhizomes may result in erratic control as Johnsongrass allocates energy to shoot growth. For long-term Johnsongrass control, glyphosate (Roundup, others) is another systemic herbicide that works more effectively when applied in the fall compared to spring treatments. Glyphosate is nonselective and should be limited to spot treatments at rates required to control Johnsongrass.
Status and Revision History
Published on May 31, 2019
Getting Rid of Johnson Grass
Besides pulling out early in the season, what can I spray on Johnson grass to get it out of my lawn? I’ve been told there is nothing I can do except pull it out (there is too much and it’s too hard to pull). I’ve also been told to hand rub the blades with Roundup. What is your suggestion?
Hardiness Zone: 6b
Bob H from northern UT
As you already know, Johnson grass is tough as nails and hard to eradicate! A single plant can produce over 5,000 seeds that can lay dormant for up to 20 years. Ugh! Unless you’re dealing with a small amount, I don’t recommend trying to “pull it out” because the rhizomes usually break off easily and are left in the ground to spread. Besides, you’re more likely to end up with a back injury from trying to pull these buggers out than you are likely to get rid of them. If you yard is heavily infested, digging them out is probably not a reasonable solution either. No good management solutions exist for this type of grass short of tilling everything up and starting over. Even that’s a bad idea, because Johnson grass thrives where there has recently been a soil disturbance. So to that extent, I can only offer you a few suggestions.
The best advice I can give you is to keep established plants mowed down close to soil level. Repeated mowing (bi-weekly) will help starve the rhizomes of nutrients, eventually causing the plant to give up (we hope). Using a propane torch may also help, but be warned that some studies suggest this actually encourages re-growth when done in the spring. Late winter is a better time for torching. If you live outside city limits, heavy grazing (goats, geese, or sheep) will also help reduce plant vigor as well as spot treatment using herbicides.
If some patches of the grass are in lower concentrations in some areas, digging or tilling is effective providing that you remove all of the rhizomes (don’t just chop them up with a tiller or you will end up with a thousand more little starter rhizomes). Reseed immediately with the appropriate grass seed and keep all other Johnson grass mowed down to prevent it from spreading to the newly disturbed area by seed. You’re probably going to have to employ a number of these strategies (and a few years of patience) in order to rid yourself of this invasive menace completely.
Grassy Weeds – Dallisgrass, Johnsongrass, Fescue Clumps, et al
For practical purposes, we are lumping together the above weeds, along with johnsongrass, orchardgrass, quackgrass, and assorted others. These are all summer grassy weeds, and all are treated in much the same manner. Most of them look surprisingly alike to the average homeowner, identifiable only by their seed heads.
NOTE: Proper mowing, watering, and fertilizing are crucial to the control of these weeds. A lawn full of grassy weeds usually signifies another underlying problem. Thick, healthy bermuda grass should choke them out. If there is encroaching shade, or if the lawn has not been fertilized in a while, not watered well, or not mowed frequently enough, grassy weeds will come in and take over. If you have shade issues where your bermuda is thinning out, please see our Shade Solutions.
You may notice that nutsedge or “nut grass” is not included. Nutsedge is actually a sedge, not a grass. For more info on nutsedge, please see our nutsedge page.
Grassy weeds are some of the toughest “problem weeds” in lawns. Why? Because your lawn is grass, and your weeds are grass, too. Dallisgrass, for example, (pictured below right) is the exact same type of grass as bermuda grass. Fertilize the bermuda grass and you’re fertilizing your weeds. Spray something on the weeds, and you’ll harm the bermuda grass around it.
So. You see what we’re up against. There is no pre-emergent, like we have for crabgrass, for these grassy weeds.
If you have a bad grassy weed problem in your lawn, it may take a full season to get them under control. Basically, we treat them with a post-emergent product that requires consistent 80⁰+ temperatures to be effective. So, if it’s still early spring and we’re still having cooler temperatures, we aren’t able to treat them.
Rest assured, if we saw them in your lawn and were unable to treat them at that time, we have put in a future service call to take care of them once temperatures exceed 80⁰.
When we do treat these weeds in the hot summer, the treatment will cause temporary yellowing in your bermuda where we sprayed the weeds. We also may have to come back and treat them again. But yellowing will be gone in several mowings and your bermuda will look good as new – minus the weeds.
Only one of the above weeds is a cool season grass – fescue (pictured below.) We use fescue grass as a shade grass here in Tulsa. If you overseed your fescue grass in the fall (as you should) or, if your neighbors do, some stray seeds will usually get out in your bermuda grass (pictured below, fescue clump in dormant bermuda.) We can treat fescue in the winter while your bermuda is still dormant, because the fescue is active. None of the other weeds are active in the winter, so we have to wait until they come up in the spring, and then we can’t treat them until it’s over 80⁰.
Proper mowing, watering, and fertilizing are crucial to the control of these weeds. A lawn full of grassy weeds usually signifies another underlying problem. Thick, healthy bermuda grass should choke them out. If there is encroaching shade, or if the lawn has not been fertilized in a while, not watered well, or not mowed frequently enough, grassy weeds will come in and take over. If you have shade issues where your bermuda is thinning out, please see our Shade Solutions.