Introduction and spread of Johnsongrass in the United States

This perennial grass can grow up to 6’ tall, with 2’ long leaves and purple flowers.  Native to the Mediterranean, this noxious weed was originally brought to the U.S. as a forage crop.  It is now established throughout the southern U.S. and is steadily creeping north.  Johnsongrass forms dense stands and crowds out native vegetation.  The plant spreads naturally by rhizomes in the soil or by seed.  Humans are likely responsible for spreading the plant, too, as rhizomes can be transported in soil stuck to machine tires or tracks.  Johnsongrass is especially common in disturbed areas, along roadsides, pastures, fields, and forest edges.  Management is difficult, but frequent grazing or mowing can eventually reduce plant populations.  Several herbicides are effective for johnsongrass management.  Hand removal is only effective in small areas, and no biological control agents are known.  Flooding can kill rhizomes, but will not damage seeds.