Cogon grass typically does not invade closed forests unless they are degraded for agriculture or lumbering. It is very successful in areas that are frequently burnt, overgrazed, or intensively cultivated and rapidly colonizes such disturbed sites. A high root-rhizome to shoot ratio provides I. cylindrica a substantial source of regeneration following cutting or burning. Its rhizomes are very resistant to heat and breakage and may penetrate soil up to 1.2 m deep, but generally they only reach the top 0.15 m in heavy clay soil and the top 0.4 m in sandy soils. Its capabilies of recovery and colonization after fire allow it to take advantage of slash and burn forestry practices (Bryson & Carter, 1993, Peet et al, 1999; Chikoye, 2003; Van Loan Meeker and Minno, 2002).

A fast-growing species, I. cylindrica thrives in areas of minimal tillage, such as orchards, lawns, and roadsides. It does not generally survive regular, deep tilling. While cogon grass is tolerant of a wide variety of soil conditions, including variations in fertility, organic matter, and moisture, it grows best in relatively acidic soils (pH 4.7). Temperature markedly affects shoot and rhizome growth, with increased growth occurring at 29º/23ºC (day/night). Temperatures of -4.5°C or lower for exposure periods of 24 hours were found to be lethal to rhizomes (Wilcut et al., 1988). While in general rhizomes do not exhibit extreme cold hardiness, stands of cogon grass may survive temperatures as low as –14ºC (Langeland and Burks, 1998; Van Loan Meeker and Minno, 2002).

I. cylindria assimilates carbon via the C4 photosynthetic pathway (Paul & Elmore, 1984) giving it a competitive advantage over C3 plants in many conditions and contributing to its invasiveness. It is a strong competitior for water, light and nutrients because it sprouts and grows more rapidly than most crops. However, like other C4 plants it is relatively intolerant of shade.

Increases in I. cylindrica concern ecologists because this species displaces native plant and animal species and alters fire regimes (Lippincott 1997 2000, in Brewer & Cralle 2003). Dense swards of I. cylindrica create an intense competitive environment for commercially important species (Bryson and Carter 1993, Kuusipalo et al. 1995, Premalal et al. 1995, Dozier et al. 1998).

Displacement: Invasion of longleaf pine communities by I. cylindrica will likely cause significant losses of short habitat-specialists and reduce the distinctiveness of the native flora of these threatened ecosystems (Brewer 2008).

Agricultural: The interference of I. cylindrica with the growth of tropical crop species, both herbaceous and woody, is well documented (Brook 1989, in King & Grace 2000b).

Habitat alteration: I. cylindrica invasion of an emerging pine forest may be an example of a grass converting a woodland with high understory diversity into a grassland with low diversity. I. cylindrica presents a case where its ability to deprive competitors of N may lead to the conversion of the ecosystem (Daneshgar & Shibu 2009).

Modification of nutrient regime: The changes in nutrient cycling caused by exotic grasses can endanger young tree seedlings in a regenerating forest (Daneshgar & Shibu 2009). Because I. cylindrica allocates significant carbon below-ground, it is able to recover quickly after fire, which is why Lippincott (2000, in Daneshgar & Shibu 2009) suggested that frequent intense fires could convert a pine savanna into an I. cylindrica-dominated grassland.

Ecosystem change: A study by Holly and colleagues (2008) supports the growing consensus that invasive plant species alter normal ecological processes and highlights a possible mechanism (alteration of microbial assemblages) by which I. cylindrica may alter an ecosystem process (decomposition).

Competition: The results of a study by Brewer and Cralle (2003) suggest that I. cylindrica is a better competitor for phosphorus than are native pine-savanna plants, especially legumes. The competitive effects of this species on plant diversity may be of more immediate conservation concern relative to the effects of this species on fire regimes in longleaf pine ecosystems (Brewer 2008).

Threat to endangered species: Longleaf pine savannas of the southeastern USA contain extraordinarily species-rich plant communities and are home to numerous threatened endemic plant and animal species (Walker & Peet 1983, Bridges & Orzell 1989, Brockway & Lewis 1997, in Brewer & Cralle 2003).

Inhibits other species: The extensive rhizome network of I. cylindrica not only allows rapid regeneration of foliage, but also produces allelopathic root exudates that can inhibit germination and growth of other plants, including some pines (Hussain et al., 1994, in Ramsey et al. 2003).

Modification to fire regime: Lippincott (2000) found that sandhill invaded by I. cylindrica had significantly greater fine-fuel loads that resulted in fires that had higher maximum temperatures at greater heights. Fire-induced mortality of juvenile longleaf pine was higher for pines growing in invaded sandhill.

Other: The density of the below-ground rhizome network makes I. cylindrica a mechanical hindrance to root growth of native species. The rhizome tips are sharp: they may even penetrate the roots of native species, leading to damage or mortality by infection (Eussen & Soerjani 1975, in Daneshgar et al. 2008).

Preventative measures: A Risk assessment of Imperata cylindrica for the Pacific region was prepared by Pacific Island Ecosystems at Risk (PIER) using the Australian risk assessment system (Pheloung 1995). The result is a score of 19 and a recommendation of: reject the plant for import (Australia) or species likely to be a pest (Pacific).\r\n

Results from a study by King and Grace (2000a) suggest that efforts to prevent I. cylindrica invasion should focus on preventing I. cylindrica propagules (seeds and rhizomes) from reaching sensitive communities. \r\n

Chemical control: Ramsey and colleagues (2003) report that herbicides may temporarily control I. cylindrica foliage up to 12 to 24 months (Willard et al. 1996 1997, in Ramsey et al. 2003). Without the re-establishment of desirable species, viable rhizomes will eventually allow cogon grass to re-infest the area (Shilling et al. 1995, in Ramsey et al. 2003). Controlling rhizomes with herbicides is a difficult task. A combination of glyphosate applied at 2.8 kg ai ha_1, followed by fertilization and reseeding with Bermuda grass (Cynodou doctylon) showed that rhizome reserves were sufficient for cogon grass to recover from both treatments (Johnson 1999, in Ramsey et al. 2003). In another study, cogon grass recovered after imazapyr was applied at 2.24 kg ai ha_1 in a 2-year-old loblolly pine plantation (Miller 2000, in Ramsey et al. 2003). Even these relatively high herbicide application rates there is still a remnant population of viable rhizomes that has the potential to re-infest the treated site. Further research is needed to integrate herbicide usage, which provides short-term control and a ‘‘window for re-establishment’’, with bio-control using desirable, yet highly productive plant species for long-term control (Ramsey et al. 2003). \r\n

Recommendations (Demers et al. 2008) to control cogon grass in the southeastern USA are to treat infestations in autumn (May through to October) with glyphosate and/or imazapyr herbicides. These recommendations are consistent with a wide range of studies conducted (Miller 2003, Faircloth et al. 2005, in Demers et al. 2008). Fluazifop is also an effective option (Demers et al. 2008). Guidelines for herbicide control are detailed by Demers and colleagues (2008).\r\n

Integrated management : Shade, repeated herbicide application, and mechanical control have all been used to control I. cylindrica (Macdicken et al. 1997, Terry et al. 1997, in Brewer & Cralle 2003). An integrated approach that combines burning, tillage (mechanical control) and chemical applications provide the best approach for cogon grass management (MacDonald et al. 2009). Cogon grass should first be burned or mowed, preferably in summer, to remove excess thatch and older leaves. Subsequent regrowth (of one to four months) will reduce rhizome biomass and allow herbicides to target actively growing leaves which maximises herbicide effectiveness. Once control of cogon grass has been achieved planting of desirable vegetation should occur as quickly as possible to prevent reinvasion (MacDonald et al. 2009).\r\n

Other: Brewer and Cralle (2003) found that short-lived, high-level pulses of phosphorus addition reduce the competitive advantage I. cylindrica has over native plants without negatively affecting native plant diversity. Additional work is needed, however, to elucidate the mechanism of inhibition of I. cylindrica by P addition (Brewer & Cralle 2003).