Cogongrass (Imperata cylindrica)
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.
Aggressive, colony-forming dense perennial grass 1 to 6 feet (30 to 150 cm) in height, often leaning in mats when over 3 feet (90 cm) in height. Stemless tufts of long leaves, blades yellow green, with off-center midveins. Silver-plumed flower and seed heads in late winter (south) through early summer (north). Plants arising from branching sharp-tipped white-scaly rhizomes. Federal noxious weed.
Upright to ascending, stout, not apparent, as hidden by overlapping leaf sheaths that are long hairy or not.
Mainly arising from near the base, long lanceolate, 1 to 6 feet (30 to 180 cm) long and 0.5 to 1 inch (12 to 25 mm) wide, shorter upward. Overlapping sheaths, with outer sheaths often long hairy and hair tufts near the throat. Blades flat or cupped inward, bases narrowing, tips sharp and often drooping. Most often yellowish green. White midvein on upper surface slightly-to-mostly off center (varies in an area). Margins translucent and minutely serrated (rough to touch). Ligule a fringed membrane to 0.04 inch (1.1 mm). Tough to break due to high silica content. Tan colored and persisting after winter dieback.
February to June and sporadically (or year-round in Florida). Terminal, silky spikelike panicle, 1 to 8 inches (2.5 to 20 cm) long and 0.2 to 1 inch (0.5 to 2.5 cm) wide, cylindrical and tightly branched on a reddish slender stalk. Spikelets paired, each 0.1 to 0.2 inch (3 to 6 mm) long, obscured by tufts of silky silvery-white hairs to 0.07 inch (1.8 mm).
May to June. Tiny oblong brown grain, 0.02 to 0.05 inch (0.5 to 1.3 mm) long, released within dense tufts of silvery hairy husks, often in clusters, for wind dispersal. Seeds matured after V-shaped stigma pair at grain tips shrivel and darken.
Grows in full sunlight to partial shade, dry to wet soils, and, thus, can invade a range of stands and sites. Often in circular infestations through rapid growth of branching rhizomes that fill friable soils to a depth of 0.6 to 10 feet (0.1 to 3 m) to exclude most other vegetation. Aggressively invades right-of-ways, new forest plantations, open forests, old fields, and pastures. Absent in areas with frequent tillage, but promoted by burning. Colonizes by rhizomes and spreads by wind-dispersed seeds, seeds and rhizomes contaminating soil and hay, and hitchhiking rides on mowing, logging, and other equipment. Seed fertility highly variable across the region. Highly flammable and a severe fire hazard, burning extremely hot especially in winter.
Resembles Johnsongrass, [Sorghum halepense (L.) Pers.], purpletop [Tridens flavus (L.) Hitchc.], silver plumegrass [Saccharum alopecuroides (L.) Nutt.] and sugarcane plumegrass [S. giganteum (Walter) Pers.]—all having a distinct stem and none having an off-center midvein. Also resembles longleaf woodoats [Chasmanthium sessiliflorum (Poir.) Yates], which lacks off-center midveins and silky flowers, having tufts of spiked flowers and seeds along a slender stalk.
History and use
Introduced from Southeast Asia into FL, southern LA, southern AL, and southern GA in the early to mid-1900s. Initially for soil stabilization. Expectations for improved forage unrealized. Federal noxious weed.
Found throughout FL, GA, AL, and MS with scattered infestations in SC, east TX, and LA. The current distribution can be checked at www.cogongrass.org.
- Do not plant the red-tipped cultivars (Japanese bloodgrass and Red Baron). Remove prior plantings, and control sprouts and seedlings.
- Treat when new plants are young and located through frequent surveillance of lands in infested zones.
- Minimize disturbance within miles of where this plant occurs, and anticipate wider occupation when plants are present or adjacent before disturbance.
- Repeated cultivation and planting of aggressive grasses or herbicide resistant crops can restore pastures and croplands.
- Burning and bush-mowing treatments can remove standing plants for more efficient herbicide treatments. However, burning usually causes rapid infestation expansion and can kill native shrubs and trees that constrain spread.
- Do not use or transport fill dirt, rock, hay, or pinestraw from infested lands.
- Seed production can be stopped by mowing, burning, or herbicide treatments in early stages of flowering or even shortly before flowering. However, these treatments can prompt later flowering/seeding as well.
- Clean seed and rhizomes from equipment and personnel working in infestations before leaving the infested site.
- Forage quality is low, eaten only when shoots are young and tender by horses, goats, sheep, mules, and some cattle.
Recommended control procedures
- Thoroughly wet all leaves with one of the following herbicides in water with a surfactant when grass is actively growing and at least 1to 2 feet high or older growth from June to September: Chopper Gen2* as a 2-percent solution (8 ounces per 3-gallon mix) or Arsenal AC* as a 1-percent solution (4 ounces per 3-gallon mix). Repeat applications in subsequent years may be required for eradication. A glyphosate herbicide may be tank mixed as a 2- to 5-percent solution with Chopper Gen2* at 2 percent (8 ounces per 3-gallon mix) or Arsenal AC* at 1 percent (4 ounces per 3-gallon mix). This treatment will accelerate burndown of actively growing shoots but may not improve rhizome kill.
- When safety to surrounding vegetation is desired (especially hardwoods, shrubs, and pines), apply a glyphosate herbicide as a 2- to 5-percent solution (8 to 20 ounces per 3-gallon mix). Two applications per growing season (just before flowering in spring and again in late summer to regrowth) are typically necessary. Apply in successive years when regrowth is present until no live rhizomes are observed for eradication; at the same time promote or establish desirable plants.
* Nontarget plants may be killed or injured by root uptake.