Imperata cylindrica (L.) Raeusch.

Mayotte: Imperata cylindrica flowers and fruits all year round.
New Caledonia: Imperata cylindrica enters into vegetation as soon as the soil is wet. Flowering and fruiting take place from September to December, at the beginning of the dry season.

Imperata cylindrica is very similar to I. brasiliensis Trin. (present from southern USA to northern Argentina and in the Caribbean) and I. contracta (Kunth) Hitchc. (present from southern Mexico to northern Argentina, in the Caribbean and introduced in the West Indies as an ornamental plant). However, I. cylindrica is the only species of this genus to have 2 stamens per flower (the other species have only one), moreover, it is essentially present in Africa and Asia.

Imperata cylindrica is a plant of tropical zone to hot temperate. It develops in extremely varied environments. It can be found in arid, sandy areas as well as in swampy areas or along waterways, in cultivated areas (formidable weed of many annual or perennial crops), in peri-urban areas, from sea level to about 2700 m of altitude, under rainy regimes varying from 500 to 5000 mm per year.
Primary natural forests and secondary forests with a lot of shade are not favorable to the development of this plant but can be colonized in case of disturbance; it is a very frequent weed of the clearing-burn areas. Indeed the activity of the cauline buds of the rhizomes is greatly favored by the passage of the fire or by the ploughings, in particular with the plough with discs, which by splitting the rhizomes, multiplies and disseminates the plant.

Benin: Imperata cylindrica is found throughout the country from the coastal zone around Cotonou to the northern savannahs (Tanguiéta, Segbana).
Northern Cameroon: Imperata cylindrica is a species of humid climate, very abundant in transition forest in Sudan and Guinea savanna zones. It grows preferentially in climates where annual rainfall exceeds 1300 mm.It occasionally grows in drier climates, in humid soils along the river. It tolerates short periods of flooding. This species is very sun-loving, and it grows mainly as weed of crops or as ruderal on roadsides and in open areas. It has no significant preference for the soil type.
Comoros: Sun loving plant, frequent in wetlands, especially at low altitudes up to 400 m. It is present especially in zones regularly set on fire. It is observed in the three islands.
Madagascar: Weed with powerful rhizomes, fairly widespread in the highlands and the eastern side of the island. It infests fallows and crops on terraces with deep soil down slopes and on alluvial plains. The presence of this weed is often considered as a degradation of soil fertility.
Mauritius: absent.
Mayotte: Imperata cylindrica is an exotic species. Weed of crops in burned areas, because fire favors the germination of seeds and limits the competition. It is present in crops, pastures and also in padza (deforested and strongly gullied areas with red lateritic soil).
New Caledonia: Species of humid climate (greater than 1500 mm rainfall), it prefers deep and draining soils. It is found preferentially on acidic soils in New Caledonia where it could be native. It spreads in areas often burned, because fire stimulates the regrowth of the plant.
Reunion: absent.
Seychelles: absent.

Global harmfulness
 
Imperata cylindrica is included in the IUCN list of the 100 most invasive species in the world, as well as the 18 most damaging weeds in the world.
I. cylindrica is capable of invading many different types of environments and preventing the natural regeneration of native species. One of the major reasons for the invasiveness of this species is its rhizome network, concentrated in the first 20 centimeters of soil, particularly dense and efficient and immune to fire and some control methods. The colonization of a new environment by this plant induces deep changes in the functioning of the concerned ecosystem. Finally, it is a recognized and feared weed for many crops, even in its native area. I. cylindrica is a rhizomatous species whose expansion in the plots is greatly favored by the actions of splitting at the time of the cultural operations (ploughing, weeding, ridging). Ploughing with a disc plow during rainy periods is the most favorable case of multiplication.
Brook (1989), cites up to 64.5 million ha of overgrown grassland in Indonesia, 5 million ha in Papua New Guinea and 300,000 ha in Fiji; more than 40% of rubber plantations in Java and 1.5 to 2 million ha of plantations in Malaysia are affected by the plant. Millions of hectares of grassland in West and Central Africa are abandoned due to the presence of this weed. The area of plantations and agricultural land colonized by this species worldwide is estimated at more than 200 million hectares.
 
Local harmfulness
 
Northern Cameroon: I. cylindrica is considered a major local weed.
Comoros: This weed grows in cassava crops and in all cultures with tubers plant, for which it represents a major problem because the pointed rhizomes of I. cylindrica that perforate tubers in the cultures. Moreover, it makes the soil compact and difficult for weeding. It is also an important weed of grasses in meadows.
Kenya: Rare but abondant when present
Madagascar: Invasive weed and harmful for rainfed crops slightly intensified (cassava, upland rice Tavy, sweet potato). It often occurs as a dense stand of variable size and poses a serious problem to the development of already infested land (weak equipment and facilities available to farmers).
Mauritius: absent.
New Caledonia: It remains moderately invasive on pasture, and is frequently found in waste lands and savannas in small stands.
Reunion: absent.
Seychelles: absent.
Tanzania: Frequent but not abundant.
Uganda: Frequent and usually abundant.

Global control
 
Imperata cylindrica is a rhizomatous species whose expansion in the plots is greatly favored by splitting parts of it at the time of cultural operations (plowing, weeding, hilling). Imperata cylindrica is a difficult species to control. Tillage with a plow at the beginning of the dry season, brings many rhizomes at the surface, causing them to dry out. This species is insensitive to pre-emergence herbicides and contact, however it is sensitive to systemic post-emergence herbicides.
For perennial grass weed control tips for irrigated rice and lowland in Africa, visit: http://portal.wiktrop.org/document/show/33

Chemical control: A chemical control can be considered during the vegetative phase with fairly high dose of glyphosate (2880 g / ha) absorbed by the leaves and penetrating the rhizomes, killing of the plant within 4 to 6 weeks. The haloxyfop (864 g / ha) also proves to be effective, however, regrowth is possible. In the case of discharges, it is advisable to deal with localized applications. In all cases, ensure the rapid implementation of new forage species able to cover the space quickly.

 
Local control

Comoros: The management of this species is practiced with weeding stakes made of iron or wood, to extract the rhizomes.
Madagascar: Tillage aids to the multiplication of I. cylindrica by splitting the rhizomes. It is also favored by fires and / or overgrazing, re-developing very rapidly from its rhizomes, which allows it to dominate other plants. It is insensitive to most selective herbicides of crops and supports short floods. However, it can be quickly controlled during seedlings: glyphosate treatment (1800 to 2160 g / ha) and maintain the mulch.(which seems to have a limiting effect on its recovery)  that have been formed allow the growth of a culture that one can associate with a vegetal cover (Mucuna, stylosanthes, brachiaria, etc.), which thus allow to keep this vegetal pest in shade and destroy it.
New Caledonia: Although it is difficult to control, I. cylindrica can be treated mechanically by plowing during dry weather, so that the rhizomes dry in the sun, repeating the operation if necessary. Never burn as it increases its proliferation.

 

Herbarium pictures ReCOLNAT: https://explore.recolnat.org/search/botanique/simplequery=Imperata%2520cylindrica