Johnsongrass - Sorghum halepense (L.) Pers.

David J. Moorhead, The University of Georgia, October 2003

Plant: Erect rhizomatous, perennial graminoid, 1-3m tall, branched from base with broad, long green leaves with prominent white midveins, from scaly sharp rhizomes and forming dense stands. Rhizomes can be as much as 1 cm in diameter and 2 m long. Plant toxic (prussic acid or hydrocyanic acid), if fertilized heavily or drought stricken.

Stem (culm): Stout, hairless, pink to rusty red near base, somewhat upward branching.

Leaves: Alternate, long- lanceolate, 20-60 cm long and 1-3 cm wide, green, with white midvein above, margins rough, prominent white-fringed membranous ligule at base of leaf, hairless except on white flared throat and a hair patch behind the ligule.

Flowers: Apr. - Nov. Open spreading purplish panicle, 15-50 cm long, with numerous whorled projecting branches being shorter in the upper portion, spikelets in pairs at the end of finer branchlets, one spikelet stemless and ovoid and the stemmed and narrow, 4-6 mm long, husks shiny and short hairy, either green, yellow, purple, or black, tipped with a thread-like awn, 5-13 mm long or absent.

Seeds: May- Mar. Awned, ovoid seeds are dark reddish- brown, released within the husks.

Range: Exotic and naturalized from Mediterranean area. CA to FL and north to MA and west to NE and OK.

Ecology: Occurs as dense colonies in old fields and along field margins and right-of-ways, where it invades new forest plantations, open forests, and forest openings. Highly competitive with planted and natural tree seedlings. Persists and colonizes by rhizomes and spreads by seeds.

Recommended Control Procedures

• Thoroughly wet foliage with a 2% glyphosate solution (8 ounces per 3 gallon mix) with a surfactant when plants are 18 inches tall to early flowering stage.
• Over-the-top of loblolly pine seedlings - apply mix of 8 ounces of Arsenal AC herbicide + 1-2 ounces of Oust herbicide per broadcast acre.
• Close frequent mowing throughout the growing season will weaken rhizomes and prevent seed production. Will persist with infrequent mowing.
• Fall to winter cultivation exposes cold-sensitive rhizomes to winter temperatures 27^o F (-5^o C). Limited early growing season tillage encourages spread of actively growing rhizomes.
• Dormant season and spring prescribed burns may encourage regrowth.

References:

James H. Miller, USDA Forest Service, Auburn, AL. personal correspondence

Miller, J.H. and K.V. Miller. 1999. Forest Plants of the Southeast and Their Wildlife Uses. Southern Weed Science Society. Auburn, AL. Craftmaster Printers.

Smith, T.E.(ed.) 1993. Missouri vegetation management manual. Missouri Department of Conservation. pp. 68-77.

Snyder, S. A. 1992. Sorghum halepense. In: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (2003, October). Fire Effects Information System, [Online]. Available: http://www.fs.fed.us/database/feis/ [9 October 2003].