Idaho OnePlan recommends the website of the Idaho Weed Awareness Campaign as the best resource for up-to-date information about Idaho's noxious weeds, and their control.
Source for this page: Idaho's Noxious Weeds by Robert H. Callihan & Timothy W. Miller

BACKGROUND

Johnsongrass (Sorghum halpense) is a Mediterranean native brought to the U.S. as a hay and pasture grass. It spreads by seed in the north, but in central and southern U.S. it also spreads by rhizomesA creeping, underground stem. 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.

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DESCRIPTION

Johnsongrass is a perennialPlant that lives for more than 2 growing seasons species over most of its range, but because it normally winter kills in Idaho, it usually acts like an annual here. Leaves are grasslike, up to 1 inch wide, with a prominent whitish midvein. The liguleThe structure at the collar of a grass leaf between the sheath and the stem is short and membranous with a hairy fringe; auriclesLobelike structure at the collar of a grass leaf are lacking. Stems can grow up to 8 feet in height, but our annualPlant that germinates, flowers, seeds, and dies during one growing season specimens will be closer to 3 or 4 feet tall. Large, open paniclesA much branched inflorescence 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 rhizomesA creeping, underground stem are produced from the crownThe structure formed where leaves, stems, and roots grow together.

DISTRIBUTION

Johnsongrass is found throughout the southern two-thirds of the lower 48 states.

CONTROL

No biological control agents are available for Johnsongrass, but herbicides are available that can control this weed.