Johnsongrass can produce toxic levels of hydrocyanic acid when under moisture stress or after frosts . Johnsongrass is the sixth most serious weed in the world. Leaves are grasslike, up to 1 inch wide, with a prominent whitish midvein. Stems can grow up to 8 feet in height, but our annual specimens will be closer to 3 or 4 feet tall. Large, open panicles are up to 1 foot long and emerge in midsummer.
Spikelets are reddish in color and most are tipped by bent awns.
Scaly, finger-thick rhizomes are produced from the crown . No biological control agents are available for Johnsongrass, but herbicides are available that can control this weed.