Plant of the Week
Johnsongrass
Latin: Sorghum halepense
Drive any Arkansas roadway this time of year and you’ll see expansive stands
of Johnsongrass, a weed so epidemic it is considered one of the nation’s ten
worst.
Let us investigate this pernicious weed and meet Col. Johnson who was
unfortunate enough to be remembered by the weed that ate the South.
Johnsongrass (Sorghum halepense) is a warm-season grass that forms
large colonies from stout, finger-sized, much-branched rhizomes. A medium-sized
plant can produce up to 60 feet of rhizomes in a single year.
From these rhizomes emerge a thicket of unbranched, pinkie-sized stems that
grow 5 to 6 feet tall and are topped with a foot-long open panicle of flowers
that are followed by purplish seeds. A medium-sized clump will produce two
pounds of seed.
One of the first mentions of the weed, later to be called Johnsongrass, was
in 1848 when a correspondent to the Southern Cultivator described a grass
that had taken over the South Carolina plantation of Gov. John Means. One source
says the seeds were mixed in with flax seeds the governor had imported from the
Mediterranean region; another says that he ordered "guinea grass" from Turkey
about 1835. Early names for the weed were Mean’s Grass and Guinea Grass.
Arkansas had a connection in the early spread of the plant. N.D. Smith of
Washington, Ark., wrote that he had imported guinea grass seeds from Jamaica in
1842 for use as chicken feed. Not surprisingly, the crop flourished, and he
reported cutting two tons of hay per acre from each of his four cuttings per
year.
About this same time an Alabama planter named Col. William Johnson traveled
to South Carolina and acquired seeds of Governor Mean’s grass and took it to his
bottomland farm near Selma. Johnson freely shared seeds and, in a kind of
thankless notoriety, the name Johnson Grass came into common usage shortly after
the Civil War.
But, to really screw things up properly requires the long reach of the
government. In 1873, the American consul in Kingston, Jamaica procured seeds of
Guinea Grass for the Department of Agriculture. During this period the
government - and especially congressmen - sent out millions of free seed packets
to their constituents as a way of assuring they would be remembered favorably
come election day.
I find no direct evidence that Johnsongrass seed was in this seed giveaway
program, but it certainly seems plausible.
Johnsongrass is a subtropical weed that does best in the Old South where
cotton best flourished.
My first memory of Johnsongrass was one August morning when my Father rousted
us kids out of bed with "The cows are out, and the Johnsongrass is going to kill
them!" Fortunately, the cattle hadn’t eaten enough grass to cause problems, but
this little story does illustrate one of the serious flaws of Johnsongrass. It
can kill cows.
The poisonous constituent of Johnsongrass is cyanide, a most lethal toxin
that can kill a fully grown cow in an hour if enough forage is consumed.
Johnsongrass tends to produce cyanide whenever it is stressed as by drought,
insect infestation or frost. If Johnsongrass is cut at the proper stage and
cured correctly, it can be safely used for hay.
Removing Johnsongrass from the landscape is relatively easy. It cannot
survive close mowings so has never been a problem in a lawn setting. In gardens
and around outbuildings Roundup or grass-specific herbicides such as Ortho Grass
Killer will usually eliminate stands with one or two applications. Late summer
is an ideal time to spray.
By: Gerald Klingaman, retired
Extension Horticulturist
- Ornamentals
Extension News -
July 26, 2002
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