Miller, James H.; Manning, Steven T.; Enloe, Stephen F. 2010. A management guide for invasive plants in southern forests. Gen. Tech. Rep. SRS–131. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 120 p.
Johnsongrass [Sorghum halepense (L.) Pers.] is an erect, perennial, warm-season grass, with stout round stemmed, 3 to 8 feet (1 to 2.5 m) tall, branching from the base. It has long and wide green leaves with prominent white midveins and tall cone-shaped reddish flower heads in midsummer that yield abundant husked tiny blackish seeds in fall. Persists and colonizes by rhizomes and spreads by seeds. New plants can produce seeds the first year. Each rhizome segment can sprout. Occurs as dense colonies in old fields, along field margins, and rights-of-way where it invades new forest plantations, open forests, and forest openings. Rapidly spreading along roadsides through mowing. Still planted as a pasture grass in some subregions, even though the plant can be toxic to grazing animals after frost or if it is fertilized or drought stricken. Resembles several stout grasses when young, while the seed head shape is more unique 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, the leaf base is often reddish tinged, and seeds are maroon on distinctly drooping seed head branches.
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.
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