Common name: Johnsongrass
Scientific name: Soghum halepense L. Pers.
Life Cycle: Perennial
Johnsongrass is a coarse-textured perennial grass that grows well in pastures, landscape beds, gardens, fields, and roadsides and is highly competitive for soil water in these sites. This weed was introduced into the southern United States as a forage grass, escaped into cultivated fields, and subsequently invaded other sites. Johnsongrass is robust and can reach heights of 10 feet under good growing conditions. Individual leaves can be between 10-25 inches long, and the root system is fibrous and dense.
Johnsongrass reproduces from seeds and underground rhizomes (creeping rootstalks). Seeds germinate most readily at soil temperatures above 65 degrees, while the rhizomes will begin growth at temperatures less than 60 degrees. Each panicle (flower cluster along the stem) produces several hundred seeds, which will remain viable in the soil for more than 20 years. The rhizomes can reach several feet in length and persist for three years or less under Kentucky conditions. Prolonged cold periods (less than 15 degrees) can kill rhizomes, especially if they are on the soil surface.
Johnsongrass toxicity–which might cause neurologic problems and lower spinal cord damage in horses–can occur from prolonged grazing or if a horse ingests it as a contaminant of hay. Thus, try to remove johnsongrass from paddocks and fencelines.
Johnsongrass is not easily controlled without killing desirable forage grasses. Small patches can be removed by hand or by digging the rhizomes. Mowing will prevent seed head formation but does not kill the plant because of the extensive rhizome growth underground. Remove any mowed johnsongrass from the paddock to prevent ingestion by horses. Spot spraying is effective.
This information was provided by William W. Witt, PhD, a researcher in the Department of Plant and Soil Sciences at the University of Kentucky.