Johnsongrass (Sorghum halepense)

Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Lilianae
Order	Poales
Family	Poaceae
Subfamily	Panicoideae
Tribe	Andropogoneae
Genus	Sorghum

Scientific Name

Sorghum halepense

Scientific Name Synonyms

Sorghum miliaceum

Holcus halepensis

Common Name

johnsongrass

Miller, J.H., E.B, Chambliss, N.J. Loewenstein. 2010. A Field Guide for the Identification of Invasive Plants in Southern Forests. General Technical Report SRS-119. Asheville, NC. United States Department of Agriculture, Forest Service. 126 p.

Plant

Erect, perennial, warm-season grass, 3 to 8 feet (1 to 2.5 m) tall, stout stemmed and branching from the base having long and wide green leaves with prominent wide, white midveins, from scaly rhizomes and prolific roots to form dense stands. Conicalshaped seed heads with whorled thin branches becoming shorter near the top, each terminated by multiple purplish spikelets. Caution: Plant toxic to grazing animals if fertilized heavily or drought stricken.

Stem (culm)

Stout, hairless, light green, solid with pronounced whitish swollen nodes. Larger stems branch below midplant.

Leaves

Alternate, long-lanceolate with a tapering tip, 8 to 32 inches (20 to 80 cm) long and 0.4 to 1.2 inches (1 to 3 cm) wide, green sometimes tinged maroon with a prominent wide white midvein and rough serrated margins, hairless except for occasional tufts within the flared throat of the whitish, clasping base. The ligule at the leaf base is a prominent white-fringed membrane, 0.25 inch (2 to 5 mm) long.

Flowers

April to November. Open, spreading panicles, 6 to 20 inches (15 to 50 cm) long, with numerous spaced whorls of projecting fine branches, being shorter in the upper portion. Flattened spikelets in pairs, crowded and overlapping at the end of finer branchlets, 1 spikelet stemless and ovoid, the other stemmed and narrow, 0.15 to 0.24 inch (4 to 6 mm) long. Husks shiny and short hairy, green turning straw yellow to reddish brown when mature, tipped with a thread-like awn or not. Tiny stigmas and stamens project and dangle during flowering.

Seeds

May to March. Grain shiny dark reddish brown turning black, 0.15 to 0.22 inch (4 to 5.5 mm) long, released within straw-colored husks or bare.

Ecology

Occurs as dense colonies in old fields and along field margins and rightof- ways to invade new forest plantations, open forests, and forest openings. Highly competitive with planted and natural tree seedlings, and excludes native plants. Persists and colonizes by rhizomes and spreads by seeds. New plants can produce seed in the first year and seed can remain dormant for many years. Each rhizome segment can sprout. Older plants flattened by running water or vehicles can sprout at each stem node.

Resembles

Resembles several stout grasses when young, while the seed head shape is more similar to the other sorghum species that are crops and the common native grass, purpletop tridens [Tridens flavus (L.) Hitchc.], whose leaves have only a thin whitish midvein, leaf base is often reddish tinged, ligule is a hairy fringe, and seeds are maroon on distinctly drooping panicle branches.

History and use

Introduced in the early 1800s and widely planted as a forage grass and still utilized in some locations. Multiple varieties developed that resulted in cold hardiness and a rapid spread northward.

Distribution

Found throughout the region with scattered dense infestations in every State. Especially frequent along highways, roadsides, and in pastures and hayfields to spread into forest margins and openings.

Management strategies

• Do not plant.
• Treat when new plants are young to prevent seed formation.
• Pull and excavate all rhizomes, cut, and treat before seed are present.
• Minimize disturbance within miles of where this plant occurs, and anticipate wider occupation when plants are present before disturbance.
• Burning treatments are suspected of having effect due to persistent rhizomes.
• Sparingly eaten by cattle, sheep, and goats, while toxic at times, especially to horses.

Recommended control procedures

• Thoroughly wet all leaves with one of the following herbicides in water with a surfactant (June to October with multiple applications applied to regrowth).
  • Recommendation for mature grass control: apply Outrider* as a broadcast spray at 0.75 to 2 ounces per acre (0.2 to 0.6 dry ounce per 3-gallon mix) plus a nonionic surfactant to actively growing Johnsongrass. For handheld and high-volume sprayers, apply 1 ounce of Outrider* per 100 gallons of water plus a nonionic surfactant at 0.25 percent. Outrider* is a selective herbicide that can be applied over the top of other grasses to kill Johnsongrass, or apply Plateau* as a 0.25-percent solution (1 ounce per 3-gallon mix) when plants are 18 to 24 inches (45 to 60 cm) tall or larger.
  • Recommendation for seedling control: apply Journey* as a 0.3-percent solution (1.2 ounces per 3-gallon mix) before Johnsongrass sprouts and when desirable species are dormant or apply a glyphosate herbicide as a 2-percent solution (8 ounces per 3-gallon mix) directed at the infestation.

* Nontarget plants may be killed or injured by root uptake.

Images

July	June	June	September
June	June	November

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