Johnson grass or Johnsongrass, Sorghum halepense, is a plant in the grass family, Poaceae, native to the Mediterranean region, but grows throughout Europe and the Middle East. The plant has been introduced to all continents except Antarctica, and most larger islands and archipelagos. It reproduces by rhizomes and seeds.
- Foliage that becomes wilted from frost or hot, dry weather can contain sufficient amounts of hydrogen cyanide to kill cattle and horses if it is eaten in quantity.
- The foliage can cause 'bloat' in such herbivores from the accumulation of excessive nitrates; otherwise, it is edible.
- It grows and spreads so quickly, it can 'choke out' other cash crops planted by farmers.
This species occurs in crop fields, pastures, abandoned fields, rights-of-way, forest edges, and along streambanks. It thrives in open, disturbed, rich, bottom ground, particularly in cultivated fields. Johnson grass resistant to the common herbicide glyphosate has been found in Argentina and the United States. It is considered to be one of the ten worst weeds in the world.
It is named after an Alabama plantation owner, Colonel William Johnson, who sowed its seeds on river-bottom farm land circa 1840. The plant was already established in several US states a decade earlier, having been introduced as a prospective forage or accidentally as a seedlot contaminant.
The 1889 book The Useful Native Plants of Australia'’ records that Sorghum halepense is a "strong, erect-growing species, varying from two to ten feet high, succulent when young, a splendid grass for a cattle run, though not much sought after by sheep. It is a free seeder. The settlers on the banks of the Hawkesbury (New South Wales) look upon it as a recent importation, and seed of it has been distributed under the name of Panicum speciabile. (WooUs) Coast of Queensland, New South Wales, and Western Australia."
- Western Farm Press. Johnsongrass resistance to glyphosate confirmed in Argentina[permanent dead link], Aug 28, 2006. (accessed 2010.01.06)
- Monsanto. Glyphosate-resistant Johnsongrass Confirmed in Two Locations Archived 2011-07-14 at the Wayback Machine, March 12, 2008. (accessed 2010.01.06)
- Delta Farm Press. Glyphosate-resistant Johnsongrass in Mid-South Archived 2008-05-11 at the Wayback Machine, March 19, 2008 (accessed 2010.01.06)
- BugwoodWiki  Holm, L. G., P. Donald, J. V. Pancho, and J. P. Herberger. 1977. The World's Worst Weeds: Distribution and Biology. The University Press of Hawaii, Honolulu, Hawaii. 609 pp.
- Dept of Soil and Crop Science, Texas A & M University
- Ohio State Uni. Agricultural Research and Development Center
- J. H. Maiden (1889). The useful native plants of Australia : Including Tasmania. Turner and Henderson, Sydney.
- Johnsongrass – US Department of Agriculture
- Kansas Wildflowers and Grasses – JOHNSON GRASS page. Includes photos.
- Species Profile- Johnsongrass (Sorghum halepense), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Johnsongrass.