Johnsongrass [Sorghum halepense (L.) Pers.] is a warm-season perennial bunchgrass that can grow up to 6 ft tall. It is best adapted to clay soils, spreads by rhizomes and seeds, and is drought tolerant. Johnsongrass can be found along roadsides and in annual and perennial fields and can rapidly become a troublesome weed in hayfields. It is a great forage for cattle grazing; however, it does not tolerate grazing pressure well. While a good alternative for cattle grazing, it is not recommended that Johnsongrass is grazed by horses due to the possibility of occurrence of equine cystitis.
Johnsongrass is high-quality forage and cattle tend to select it in pastures to graze. Protein level tends to average 12% with total digestible nutrients (TDN) around 55%. Under grazing, animals should be turned in when canopy height is between 15 and 18” and the target stubble height recommended is 6 to 8”. It does not tolerate continuous stocking or high grazing pressure management well and rapidly plays out. Under grazing, it is recommended to be cautious to put cattle to graze after the occurrence of prolonged drought or frost. These environmental conditions can result in the accumulation of prussic acid in the leaves while nitrate can also accumulate to toxic levels. It is recommended to wait up to two weeks after the drought or frost event has occurred before turning the animals in to graze to allow for dilution of built-in compounds after plant growth and metabolic functions are restored.
It can be used to produce hay, but it may be challenging to dry. Johnsongrass’ growth potential can outcompete other warm-season grasses (i.e., bahiagrass, bermudagrass) and tall fescue in hayfields which creates dense patches throughout the fields. In terms of control, intensive mowing johnsongrass patches can help once the plant does not thrive under high-intensity defoliation management. When necessary, herbicides can be used but recommendations should take into consideration what perennial grass is predominant in the hayfield to avoid damage. Spot spraying with glyphosate may be an option and other products such as Prowl H2O, Pastora, and Outrider can be used. For further help on controlling Johnsongrass on your hayfields, please contact your local Extension agent at https://www.clemson.edu/extension/livestock/team.html.
Submitted by Liliane Silva, Ph.D., Assistant Professor and Extension Specialist,
Forage-Livestock Systems, Department of Animal and Veterinary Sciences, Clemson University
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