It will behoove you to nip the nasty grass in the bud as soon as you spot it.
Johnsongrass taking over.
Johnsongrass is not too unrelated from Sorghum. Because of this, it is thought that Colonel WIlliam Johnson tried this as a crop to determine if it would be palatable and therefore successful. Fast forward a century and a half later and we are dealing with a vigorously spreading dense and tall grass native to Asia. It spreads both via Rhizomes and a high percentage germinating seed. It is quick to take over pastures and hayfields, and, as luck has it, is poisonous for ruminants when the grass experiences stress or decays.
Recently, we scoured and searched over 2,000 acres for clumps of Johnsongrass to kill it before it produces viable seed.
HOW TO IDENTIFY JOHNSONGRASS
Johnsongrass is an unmistakable broad, long bladed grass that has a bit of a brighter green than most common fescues or pasture grasses and legumes. Quick growing, the grass can be spotted exceeding twice the height of its surrounding grasses only weeks after mowing or haying. The inflorescence is a magenta-pink that can be mistaken for Tridens flavus (Purpletop Tridens) when the seedhead is first coming out of the sheath of these large stalks of grass.
The stiff, stalky, tall, broad-bladed Johnsongrass shown below with viable seed heads.
HOW TO CONTROL JOHNSONGRASS
The only viable way to control Johnsongrass is to spray a non-selective herbicide. Depending on the amount of Johnsongrass on the property in question, spot spraying may be all that is necessary. However, If Johnsongrass is allowed to produce viable seeds then one can expect some recurring applications for some years to come.
A pasture nearly rid of Johnsongrass after our work on this large farm in Southern Albemarle. Pictured below is Tridens Flavus, a stunning native that has a deeper purple inflorescence.