Taxonomic name: Imperata cylindrica (L.) Beauv.
Synonyms: Imperata arundinacea Cirillo, Lagurus cylindricus L.
Common names: alang-alang, blady grass (English), Blutgras (German), carrizo, cogon grass (English), gi (Fijian), impérata cylindrique (French), japgrass (English), kunai, lalang, ngi (Fijian), paille de dys (French), paillotte (French), satintail (English), speargrass (English)
Organism type: grass Imperata cylindrica is considered one of the 10 worst weeds in the world and has been reported by 73 countries as a pest in a total of 35 crops. It is one of the most noxious colonisers of degraded humid tropical forest soils and often invades abandoned shifting-cultivation areas. In Southeast Asian, Imperata cylindrica grasslands are largely considered unproductive wastelands and its total coverage throughout the tropics (natural grasslands included) is estimated at 2,000,000 km². Description
Cogon grass is an erect, perennial grass, with linear to lanceolate, mostly basal leaf blades up to 1.5 metres tall and to 2 centimeters wide (Gabel 1982; Lippincott 1997; Langeland and Burks 1998, in Van Loan Meeker and Minno 2002). Culms are mostly erect and unbranched, with reduced blades and open sheaths (Holm et al. 1977; Bryson and Carter 1993 in Van Loan Meeker and Minno 2002). Pubescent at their base, leaf blades have a noticeably off-center whitish midvein and scabrous margins. Varying in form, from loose to compact tufts, cogon grass is strongly rhizomatous with extensive, sharply pointed, creeping scaly rhizomes (Holm et al. 1977; Langeland and Burks 1998 in Van Loan Meeker and Minno 2002). Panicles (6 to 22 centimetres long by 3.5 centimetres wide) are plume-like, cylindrical, dense, and silvery (Holm et al. 1977; Lippincott 1997; Langeland and Burks 1998 in Van Loan Meeker and Minno 2002). Spikelets are 3 to 6cm long, crowded and paired on unequal stalks, with each spikelet surrounded by white hairs up to 1.8mm in length (Bryson and Carter 1993; Langeland and Burks 1998 in Van Loan Meeker and Minno 2002). Occurs in:
agricultural areas, coastland, natural forests, planted forests, range/grasslands, riparian zones, ruderal/disturbed, scrub/shrublands, urban areas, wetlands Habitat description
I. cylindrica occurs in a wide range of habitats, including degraded forests, grasslands, arable land and young plantations (Chikoye 2003). It can be found growing in almost all eco-types from the dryest flatwoods to the margins of permanent bodies of water (Langeland and Burks 1998). Concon grass has invaded areas from highly xeric upland sites to fully shaded mesic sites; it invades sandhills, flatwoods, hardwood hammocks, sand dunes, grasslands, river margins, swamps, scrub and wet pine savanna communities. It is found mainly in tropical and subtropical areas with 75 to 500cm of annual rainfall (Bryson 1999, in Van Loan Meeker and Minno 2002). It has been found at latitiudes from 45°N (Japan) to 45°S (New Zealand), and from sea level to over 2,000m elevation (Holm et al. 1977, in Van Loan Meeker and Minno 2002).
Normally, it does not occur in closed forests but it appears once the forests are opened up for agriculture or lumbering (Ivens 1980, in Chikoye 2003). In fact, I. Cylindrica is very successful in areas that are frequently burnt, overgrazed or intensively cultivated; it rapidly colonises disturbed sites (Chikoye 2003; Peet et al. 1999). A high root-rhizome to shoot ratio provides a dry source of matter for regeneration after cutting or burning (Saxena and Ramakrishnan 1983, in Peet et al. 1999). Rhizomes are very resistant to heat and breakage and may penetrate soil up to 1.2m deep, but generally they only occur in the top 0.15m in heavy clay soil and in the top 0.4m in sandy soils (Holm et al 1977, Bryson and Carter 1993, in Van Loan Meeker and Minno 2002). Because of its success following fires this grass is often associated with slash and burn forestry practices (Chikoye 2003).
This fast-growing species thrives in areas of minimal tillage, such as orchards, lawns, and roadsides; it does not survive well under regular deep tilling (Patterson et al. 1979, in Langeland and Burks 1998). While congon 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) (Hubbard et al 1944, Wilcut et al. 1988, in Van Loan Meeker and Minno 2002). Temperature markedly affects shoot and rhizome growth, with increased growth occurring at 29º/23ºC (day/night) (Patterson et al. 1980, in Van Loan Meeker and Minno 2002). In general, rhizomes do not exhibit extreme cold hardiness, but stands of cogon grass have survived temperatures as low as –14ºC (Wilcut et al. 1988b in Van Loan Meeker and Minno 2002). General impacts
I. cylindrica is considered to be one of the worst weeds in southeastern Asia and the moist savannas of West Africa (Garriety et al. 1997; Terry et al. 1997, in Chikoye 2003). The tenth most infamous weed in the world, it affects farmers who practice slash-and-burn agriculture (Holm et al. 1977 in Chikoye 2003). Noxious because of its wide distribution, adaptation to a wide range of climatic conditions and soils and high competitive ability I. cylindrica is resistant to many control methods including burning (Chikoye 2003). Dry and vast Imperata wastelands are highly prone to frequent and intense fires, which destroy native vegetation and hamper the succession of native plants by killing shoots (Eussen and Wirjahardja 1973; Dela Cruz 1986 in Jussi et al. 1995). Natural regeneration of tree vegetation on alang-alang grasslands is retarded or impossible due to the plant's high competitive ability (Jussi et al. 1995). Following fires, I. cylindrica regenerates very rapidly from its underground rhizome system and may dominate on sites previously disturbed by slash and burn agriculture for up to 7 years (Chikoye 2003; Kushawa, Ramakrishnan and Tripathi 1983, in Peet et al. 1999).
I. cylindrica can significantly alter the structure and function of invaded communities (Holm et al. 1977, Wilcut et al., Lippincott 1997, in Van Loan Meeker and Minno 2002). It can invade disturbed ecosystems, forming dense mats that make it nearly impossible for other plants to coexist (Chikoye 2003). It displaces a large variety of native plant species and in turn the native animals that depend on them for forage and shelter (Chikoye 2003). Some ground-nesting species are also displaced (Johnson and Shilling Undated). Cutting and burning practices associated with Imperata grasslands in Nepal threaten less mobile species (and species less tolerant to disturbance) such as the pygmy hog and hispid hare (Oliver 1980, Bell, Oliver and Ghose 1990, in Peet et al. 1999). There is ample evidence that regular fires (including those associated with Imperata) can affect and reduce the relative and absolute abundance of small mammals, herpetofauna and invertebrates (Cheesman and Delany 1979, Fa and Sanchez-Cordero 1993, Friend 1993, Fyfe 1980, Barbault 1983, Gillon 1983, Braithwaite 1987, Gillon 1970 1983, Ahlgren 1974, Majer 1984, Anderson 1991, in Peet et al. 1999).
The harmful effects of I. cylindrica on crops are well documented (Holm et al. 1977, Townson 1991, in Chikoye 2003). It negatively affects the growth of teak, cocoa, kola, coffee, cashew, oil palm, coconut, rubber, and Gmelina arborea (Komolafe 1976; Holm et al. 1977; Townson 1991, in Chikoye 2003). Yields of annual crops are severely reduced by competition from I. cylindrica which can cause yield reductions of up to 80% to 100% (Koch et al. 1990; Udensi et al. 1999, in Chikoye 2003). Complete crop failure usually occurs when crops are grown in slashed plots without additional weeding. In cassava yield losses of 50 to 90% have been reported (Koch et al. 1990; Chikoye et al. 2001, in Chikoye 2003). In addition to yield loss, I. cylindrica increases the cost of crop production, reduces the market value of damaged tuber and root crops, and increases the risk of fire in perennial crops, plantations, and forest reserves. Recurrent bush fires during the dry season cause considerable loss of organic matter, which results in soil degradation. Mechanical injuries to the skin caused by rhizome ramets in highly infested areas reduces the efficiency of planting, fertilizer application, staking, weeding, and harvesting and results in increased labour demand and the abandonment of land (Holm et al. 1977; Terry et al. 1997, in Chikoye 2003). Geographical range
Native range: A native to southeast Asia, I. cylindrica is found throughout the temperate and tropic zones. The exact center of origin of I. cylindrica is in doubt, but is believed to be East Africa (Evans 1987 1991, in Van Loan Meeker and Minno 2002). Imperata cylindrica var. major originated in Southeast Asia and occurs throughout the tropical and warmer regions of the world, from Japan to southern China, through the Pacific islands, Australia, India, East Africa, and the southeastern United States (Holm et al. 1977, in Van Loan Meeker and Minno 2002).
Known introduced range: Commonly found in humid tropics I. cylindrica has spread to warm temperate zones worldwide (Hubbard et al. 1944, in Langeland and Burks 1998). It is widely distributed in Africa, Australia, southern Asia, and the Pacific Islands, and less extensively distributed, or a less serious problem, in southern Europe, the Mediterranean, the Middle East, Argentina, Chile, Colombia, the Caribbean, and the southeastern United States (Van Loan Meeker and Minno 2002). Introduction pathways to new locations
Ignorant possession:
Nursery trade: Sold as an ornamental in parts of the United States.
Other: Vegetative reproduction from rhizome segments is a significant factor in human spread of the species because these are often found in dirt moved as fill (Ayeni and Duke 1985, Willard 1988, Shilling et al. 1997, in Van Loan Meeker and Minno 2002).
Road vehicles (long distance): Moved with heavy equipment from job to job.
Seafreight (container/bulk): Used as a packing material.
Local dispersal methods
Off-road vehicles:
On animals (local): Disperses over long distances into a variety of habitats by windborne seeds (Bryson and Carter 1993, in Langeland and Burks 1998); distances dispersed range from an average of 15m to 100 m (Holm et al. 1977, Shilling et al. 1997, in Van Loan Meeker and Minno 2002).
On animals (local): Seed only up to several hundred metres.
Other (local): Rhizomes: the aggressive and invasive nature of I. cylindrica is attributed to its rhizomes. These are normally concentrated in the upper 15-20 cm of soil where they can remain dormant but viable for a long time (Ivens, 1980 in Chikoye 2003). Rhizomes have a high regenerative ability because of the numerous buds that readily sprout into new shoots after fragmentation by tillage or any other form of disturbance. Rhizomes are resistant to fire because of deep soil burial (Chikoye 2003).
Road vehicles:
Translocation of machinery/equipment (local): Management information
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).
Physical: Hand pulling is an option but is extremely labor intensive. Integrated management: Burning alone is not an option, as burning only will stimulate growth an extra 50-100% per year. An integrated approach is best, utilizing burning to remove thatch layer, follow with mowing or dicing, and late season (fall 3-4 weeks prior to any frost) applications of a broad spectrum herbicide such as imazapyr or glyphosate using the labelled rate for spot treatments. The Pacific Islands of Palau and Yap are effectively controlling I. cylindrica with applications of the herbicide Roundup-Pro, followed by establishment of shade providing trees. The initial application greatly reduces the stand of I. cylindrica, but in most cases several herbicide applications are needed. Trees can be planted in scalped patches within the herbicided plots. Follow-up herbicide treatments at 4-6 month intervals are needed to clean up newly emerging I. cylindrica. Care should be taken to avoid the planted trees which eventually provide shade that should effectively prevent re-establishment (Duane Nelson, USDA- Forest Service, Hawaii). Click here for more Information about management of Imperata cylindrica. Nutrition
Can be found growing in a wide range of soil types with little to no special nutrient requirements. Reproduction
Sexual through seed production and asexual through rhizome production.
Rhizome growth from 1.5-3 metres per year. Seed production in early spring with up to 3000 seed per seedhead, most of which are viable. Lifecycle stages
Perennial, adult plant life not known for certain. Seed and rhizome longevity undetermined. Definite dormancy in seeds and rhizomes, but mechanism is unknown. This species has been nominated as among 100 of the "World's Worst" invaders Reviewed by: Major update under progress
Eric R.R.L Johnson, Graduate Research Assistant, University of Florida, Gainesville, Florida USA.
Compiled by: Eric R.R.L Johnson, Graduate Research Assistant, University of Florida, Gainesville, Florida USA & IUCN/SSC Invasive Species Specialist Group (ISSG)
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Last Modified: Monday, 24 July 2006
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