Species Description: Cogongrass, Imperata cylindrica, is a perrenial, rhizomatous grass that is somewhat variable in appearance. The species puts out extensive rhizomes that give rise to 3-10' long spreading stems and the leaf blade bunches that grow out of the stems. The leaf blades begin at ground level and leaves typically range from 1-4 feet in length. Blades range from 1/2-3/4 inches in width, possess finely serrate sharp margins, a white, off-center mid-vein, and are hairy at the base. The finely serrate leaf margins contribute to the undesirable forage qualities of this grass. Young leaves are light green while older leaves are orange-brown to brown in color. The ligules (membranous or hairy appendages at the junction between sheath and blade) are brown and papery.
This grass produces long, fluffy-white panicles (seedheads) (Langland and Burks 1998, MacDonald et al. 2006).
Potentially Misidentified Species: General difficulties in grass species identification for the layperson notwithstanding, the Florida range of Imperata cylindrica overlaps with the range of another non-native congener, Brazilian satintail I. brasiliensis. These two species are morphologically and genetically very similar. Where they co-occur, they readily hybridize to yield hybrids capable of producing fertile offspring. Positive identification of the two species may require analysis of cytological, genetic and morphological attributes and some authorities consider the species to be synonymous (USDA FEIS).
Regional Occurrence: Cogongrass is native to southeast Asia, the Philippines, China, and Japan. This invasive plant that can now be found throughout tropical and subtropical regions on every continent except Antarctica. The species thrives in areas disturbed by human activities (MacDonald 2004).
Imperata cylindrica was accidentally as well as intentionally introduced to the United States in the first half of the 20th century. The species has since spread across the southeastern United States, extending from Florida to eastern Texas (Bennett 2006). I. cylindrica also extends northward to Virginia and Maryland along the east coast and into Oregon on the west coast (MacDonald et al. 2006, GBEP 2007).
In Florida, cogongrass now occurs from the Panhandle region well into south Florida.
IRL Distribution: Imperata cylindrica can be found within the IRL watershed from Volusia County south through Martin County. The USDA Plants Database currently shows the species absent from the southernmost portion of the watershed in Palm Beach County, but indicates that the species is again present to the south in Miami-Dade County.
Abundance: MacDonald et al. (2006) estimate that worldwide, cogongrass infests around 200,000 ha of agricultural land. In Florida, hundreds of hectares of reclaimed phosphate mining land have been invaded by Imperata cylindrica monocultures. Established cogongrass stands can produce more than a ton per hectare of rhizome biomass (MacDonald et al. 2006).
Reproduction: Cogongrass reproduces both asexually through the production of clonal individuals sent up from new rhizomes and also through sexual flowering and seed production. Flowering occurs primarily in the spring and also in response to stress events such as burning or mowing. Flowering is highly variable among plants and between stands and ranges from none to frequent (Sajise 1972).
Cogongrass is monoecious (male and female reproductive organs on the same individual) and the flowers are complete (having a pair of female stamens and a pair of male stigma present in each flower), but the species is an obligate out-crosser.
The small seeds are attached to plumes of long hairlike projections to facilitate wind dispersal and as many as 3,000 seeds are produced per plant (FIPR 1997, FloriData).
Embryology: Although large numbers of seeds may be produced by individual plants, only a small percentage of these successfully establish as seedlings, and obligate outcrossing leads to low overall spikelet fertilization success (Cavers 1983). Experimental evidence suggests that germination rates of fertilized caryopsis (the dry fruit, commonly called the grain) are high (> 90%), however.
The species is slow to establish from seed and seedlings have been observed to emerge from soil taken from cogongrass infested areas for up to three months following flowering. Natural recruitment of seedlings was observed in disturbed areas where survivorship beyond eight months was less than 20% but remained steady thereafter (FIPR 1997).
Temperature: Above-ground cogongrass biomass does not tolerate cool temperatures well and in warm temperate regions where the species occurs, the rhizome system usually remains dormant through the winter months (GBEP 2007). Rhizomes are susceptible to subfreezing temperatures, although Wilcut et al. (1988) reports survival of rhizome systems in Alabama despite winter temperatures of -14°C.
The optimum temperature for seed germination has been reported as 30°C (Dickens and Moore, 1974).
Hydrology: Imperata cylindrica is commonly encountered along wetland margins, but it is intolerant of conditions of prolonged soil inundation by water (GBEP 2007).
Specialized anatomy of the rhizome mat allows for water conservation and cogongrass performs well on fine sand to heavy clay soils and in soils of low fertility (MacDonald et al. 2006).
Fire Tolerance: Cogongrass rhizomes are very resistant to heat, including that generated by fire. Fire also triggers flowering and seed production in the species (Wilcut et al., 1988, FIPR 1997).
Other Physiological Tolerance: Cogongrass does not typically tolerate dense shade conditions. However, recent reports of invasion into old growth forests in Florida hint at the emergence of a more shade-tolerant ecotype (MacDonald et al. 2006).
Trophic Mode: Autotrophic (photosynthetic).
Associated Species: Imperata cylindrica thrives in disturbed and marginal habitats such as roadsides and rights-of-way, ditches and swales, pastureland, golf courses, and forest edges (capable of extending into the understory). MacDonald et al. (2006) note that cogongrass typically does not survive in actively cultivated lands.
Invasion History: Imperata cylindrica was accidentally introduced to the United States in the first half of the 20th century. Originally it arrived in the U.S. as packing material. In 1912, live cogongrass was reported near Grand Bay, Alabama, apparently derived from orange crate packing material originating from Satsuma, Japan. A decade later, cogongrass from the Philippines was intentionally planted in Mississippi as an experimental forage plant. In the 1930s and 1940s, cogongrass was also planted in Florida for use as livestock forage and for erosion control (MacDonald et al. 2006, Farm Press 2006).
Cogongrass was soon revealed to be a poor forage material, and it was a marginal sediment stabilizer as well. Instead, the grass was found to be a noxious pest species and further intentional planting of the species was prohibited. Continued illegal planting and accidental dispersal through habitat disturbance, road construction, and forage transport furthered the spread of this invasive grass (MacDonald et al., 2006). Recent spread of cogongrass into some formerly uninfested areas may be the result of accidental downstream transport of viable vegetative material that was uprooted or cut down in upstream infested habitats (Bennett, 2006).
Potential to Compete With Natives: Cogongrass has the potential to dominate disturbed and marginal areas. The thick rhizome mass allows dense monotypic stands to become established, and also confer an impressive ability to spread vegetatively. The underground rhizomes of a cogongrass stand may contain 75-85% of the total biomass of the stand (Bennett 2006).
Several authors (Casini et al. 1998, Koger and Bryson, 2004 Koger et al. 2004) also report that cogongrass rhizomes and foliage also produce and exude allelopathic (toxic, used in intraspecific competition) chemicals that further inhibit the success of co-occurring native plants.
Possible Economic Consequences of Invasion: Cogongrass is utilized as a forage in its native southeast Asia. In large part, however, there is little choice in the matter as this species is the dominant plant species over some 300 million acres of land. Even so, studies demonstrate that only very young foliage lacking the serrate leaf margins of older plants is suitable for use as forage, and that crude protein content rarely reached the minimum level considered necessary to raise cattle (MacDonald et al. 2006).
Several thousand hectares of native habitat have been degraded or lost to cogongrass invasion in the southeastern United States. Globally, the species has had serious negative impacts on the economy. It has greatly impeded reforestation efforts in southeast Asia and the primary agricultural weed in much of Africa (MacDonald 2004). Dense stands of cogongrass alter natural fire regimes and can increase both the intensity and frequency of wildfires.
MacDonald (2004) indicates that cogongrass is now considered to be one of the ten most troublesome weeds in the world. Considerable effort is being made to manage and contain this species in Florida, but carelessness and unchecked growth in areas where it now occurs allow continued spread into non-infested areas.
Despite increased vigilance in the southeastern U.S. in regard to cogongrass, varieties of the species such as "Japanese Blood Grass" (I. cylindrica var. koenigii) are still being cultivated and sold as ornamentals in other parts of the country.
Bennett, D. 2006. Cogongrass, deep-rooted sedge in Mississippi Delta. Delta Farm Press Oct 19, 2006 news story. Available online.
Casini P., and V. Vecchio. 1998. Allelopathic interference of itchgrass and cogongrass: germination and early development of rice. Trop. Agric. Vol. 75 No. 4, 445451.
Cavers P.B. 1983. Seed demography. Canadian Journal of Botany 61:3578-3590.
Dickens R., and G.M. Moore. 1974. Effects of light, temperature, KNOv3, and storage on germination of cogongrass. Agronomy Journal 66: 187-188.
FIPR. 1997. Ecology, Physiology, and management of Cogongrass (Imperata cylindriuca). Publication No. 03-107-140, prepared by University of Florida under a grant sponsored by Florida Institute of Phosphate Research (FIPR). 144 p.
Galveston Bay Estuary Program (GBEP). 2007. The Quiet Invasion: A Guide to Invasive Plants of the Galveston Bay Area. Available online.
Koger C.H., and C.T. Bryson. 2004. Effect of Cogongrass (Imperata cylindrica) Extracts on Germination and Seedling Growth of Selected Grass and Broadleaf Species. Weed Technology 18: 236-242.
Koger C.H., Bryson C.T., and J.D. Byrd, Jr. 2004. Response of Selected Grass and Broadleaf Species to Cogongrass (Imperata cylindrica) Residues. Weed Technology 18: 353-357.
Langeland K.A., and K.C. Burks (Eds.). 1998. Identification and Biology of Non-Native Plants in Florida's Natural Areas. UF/IFAS. 165 p.
MacDonald G.E. 2004. Cogongrass (Imperata cylindrica)-Biology, Ecology, and Management. Critical Reviews in Plant Science 23:367-380.
MacDonald G.E., Brecke B.J., Gaffney J.F., Langeland K.A., Ferrell J.A., and B.A. Sellers. 2006. Cogongrass (Imperata cylindrica (L.) Beauv.) biology, ecology and management in Florida. IFAS/UF document SS-AGR-52. Available online.
Sajise P.E. 1976. Evaluation of cogon (Imperata cylindrica (L.) Beauv.) as a seral stage in Philippine vegetational succession. 1, The cogonal seral stage and plant succession. 2, Autecological studies on cogon. Dissertation Abstracts International B (1973) 3040-3041. From Weed Abstracts 1976, No. 1339.
Wilcut J.W., Truelove B., Davis D.E., and J.C. Williams. 1988. Temperature factors limiting the spread of cogongrass (Imperata cylindrica) and torpedograss (Panicum repens). Weed Science. 36:49-55.