Cogongrass, Imperata cylindrica, is a perrenial, rhizomatous grass that is
somewhat variable n 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).
HABITAT AND DISTRIBUTION
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,
In Florida, ogongrass now occurs from the panhandle region well into south Florida.
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
southernost portion of the watershed in palm Beach County, but indicates
that the species is again present to the south in Miami-Dade County.
LIFE HISTORY AND POPULATION BIOLOGY
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).
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).
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).
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).
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).
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).
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.
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 be 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
(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.