What is Johnsongrass? 

Johnsongrass is a fast-growing perennial grass that originates from the Mediterranean region of Europe and Africa. Currently, it can be found in on nearly every continent with the exception of Antarctica. In North America, Johnsongrass can be found throughout the contiguous United States extending north into Southern Ontario and reaching as far south as Northern Mexico. It is believed to have been introduced as a forage crop by Colonel William Johnson in the early 1800’s. Johnsongrass, once utilized for its high-yield as a forage crop and its superior erosion control properties, is now categorized as a particularly aggressive invasive species.

What does Johnsongrass look like?

Johnsongrass seedlings can easily be mistaken for a corn or sorghum seedling; however, the stems and leaves of a Johnsongrass seedling are hairless and narrower than those of its look-a-likes. Johnsongrass leaves, at any developmental stage, have distinct white mid-veins which can help differentiate it from most other grasses. 

At maturity, Johnsongrass plants can range from 2.5 feet to over 7 feet tall. Leaves generally range from 7 to 24 inches long and are between .25 to 1.25 inches wide. Leaves have a prominent white midrib and are usually hairless.

Johnsongrass panicles (flower heads) have a distinct pyramid shape and range from 5 inches to 20 inches long. They consist of many branches that grow perpendicular to the stem at the bottom and parallel at the top. Johnsongrass seeds range from 2mm – 3mm and are egg or football shaped. They attach onto the lateral branches of the panicle and shift from a greenish-purple color when young to a dark reddish-brown at maturity. 

Another distinguishing characteristic of Johnsongrass are its roots and rhizomes. Rhizomes range in color from white to brown and may contain purple spots and nodes covered brown scaly sheaths.

Why is Johnsongrass such a big deal?

Johnsongrass is a noxious weed today for some of the same reasons it was valued in the past. Johnsongrass plants are extremely competitive and spreads quickly through rapidly-growing rhizomes. A single plant can produce over 200 feet of rhizomes in a single season and forms dense colonies which can drastically restrict crop growth and native plant life. It can also be a source of diseases and pests that can quickly infest and damage crops. 

Additionally, at certain developmental stages (when leaves or stems are actively growing) or under certain environmental conditions (drought, extreme heat, or frost), Johnsongrass may contain prussic acid (hydrogen cyanide) at levels that may be lethal to livestock. Bloat may also occur in livestock that graze on the foliage of Johnsongrass due to excessive nitrate levels. 

How is Johnsongrass controlled?

Due to the unique reproductive structures of Johnsongrass, effective control means that the roots, rhizomes, and flowers must be destroyed. For this reason, with the exception of herbicide applications, one or more control methods must be used together to control Johnsongrass.

Cultural Control

Cultural control involves land and vegetation management techniques to prevent the establishment and/or control the spread of Johnsongrass

Cultural control methods for Johnsongrass include

  • Heavy grazing of young and healthy plants (must be carried out with extreme caution)
  • Planting a dense cover crop in the spring after intensive cultivation
  • Frequent surveys of fence lines, roadway, ditches and other susceptible areas for new infestations and the quick removal of new plants

Mechanical Control

Mechanical control involves the physical removal of all parts or just the reproductive parts of the Johnsongrass plant. 

Mechanical control methods for Johnsongrass include

  • Hand-pulling or hoeing of small, recently established populations
  • Mowing or harvesting (this will prevent seed production but will not prevent reproduction via rhizomes)
  • Fall plowing may bring rhizomes closer to the surface, exposing them to winter frost.
  • Cultivation can make Johnsongrass less competitive but can allow the infestation to grow more rapidly due to the rhizomes.

Because Johnsongrass can reproduce with both rhizomes and seeds, mechanical control is time-consuming, labor intensive, and not financially practical. In general, mechanical control is not a good control option for Johnsongrass. 

Biological Control

Biological control involves the application of a living organism (pest, fungus, etc.) to control the spread of weeds. Use of the organisms will not eradicate the host plant and must be used in conjunction with other suitable control methods.

At this time there are no approved biological control methods for Johnsongrass.

Chemical Control

Herbicides may be used (in accordance with label directions) alone or in conjunction with one or more suitable control methods listed above. A variety of chemicals are available at cost-share pricing and can be purchased at our office.

What Herbicides are approved?

Herbicides currently recommended and approved for control of Johnsongrass are as follows:

  • 2,4-D (Amine or Lo-Vol Ester)
  • dicamba
  • diflufenzopyr
  • diquat
  • glyphosate
  • imazapic
  • imazapyr
  • picloram
  • quinclorac

Other products labeled and registered for use on this noxious weed in Kansas may be used in accordance with label directions but are not available for cost-share.  Be sure to follow all label directions and precautions. For additional information consult the most recent edition of the KSU publication of “Chemical Weed Control for Field Crops, Pastures, Rangeland, and Non-cropland”.

When should I apply herbicides?

Johnsongrass is typically treated from July to August. It is important to remember that regardless of the month, plants must be actively growing at the time of application in order for treatment to be effective.