Johnson Grass (Sorghum halepense)

Johnsongrass is a perennial grass that can grow up to seven feet tall. It spreads easily by rhizomes. Leaf blades are typically about 1 inch wide and up to 2 feet long. In the fall, large open seed heads that are yellow to purplish develop.

Close up of Johnson Grass
Photo: Missouri Plants

Why is it a threat?

Johnsongrass is highly invasive and can outcompete native grasses. It is frequently seen along roadsides. Thick stands of Johnsongrass decreases the diversity of native plants and decreases forage for many animals dependent on those native plants. Healthy plants can provide good forage for livestock. However, foliage of Johnsongrass can produce toxic amounts of cyanide if growing under stressful conditions, such as cold (i.e., frost), extreme heat, or drought and may be poisonous to livestock when ingested. High nitrate levels in the plant can complicate the problem and produce nitrate poisoning in sheep and cattle. All of these factors make Sorghum halepense one of the 10 most noxious weeds in the world.

Two images showing clumps of Johnson Grass
Photos: CalPhoto (L), USDA (R)


There are multiple control strategies for Johnsongrass but early action is always encouraged.

Cultural control
Prevent spread of rhizomes from infested to uninfested areas, kill or weaken established plants and their underground rhizome system, control seedlings, 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.
Chemical Control
Glyphosate can be used. University of Missouri recommends Roundup or Touchdown. Some varieties have become resistant to glyphosate and all are resistant to B/2 herbicides. Soil-applied herbicides and post-emergents are also used.


Johnsongrass is present in all US states except AK and MN. It 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.


This plant was initially introduced to the US from Turkey as a forage crop in the 1800s. While this is generally considered an agricultural pest, it also makes its way into natural systems. It is native to the Mediteranean region of Europe and Asia.