Cymbopogon nardus (L.) Rendle

Home

Graminae

Synonyms

Cymbopogon afronardus Stapf.

Common names

False citronella (Zaire), citronella grass (Taiwan), blue citronella grass (Kenya), naid grass (India).

Description

Tall tufted perennial with narrow leaf-blades. Panicle narrow, 15-30 cm long with racemes 8-10 mm long, often rather villous; sessile spikelets flat or concave on the back with winged keels, awn 5-6 cm long (Napper, 1965).

Distribution

Throughout southern and north-eastern tropical Africa, Uganda, Tanzania and Kenya.

Season of growth

Summer.

Altitude range

2 000-3 000 m.

Rainfall requirements

750 mm or over.

Sowing methods

C. nardus establishes naturally from seed in the highly grazed areas beneath bushes.

Tolerance to herbicides

Dalapon and paraquat would probably control it.

Response to defoliation

Generally C. nardus is avoided in grazing. Light grazing encourages it, but heavy grazing pressure of one bullock per hectare prevented recolonization of the species (Harrington, 1974). Periodic very heavy stocking converted a slope pasture of 47 percent C. nardus to a mixed pasture dominated by Brachiaria decumbens. The application of 158 kg N/ha increased the content of B. decumbens still further (Harrington & Thornton, 1969).

Response to fire

It is very resistant to fire and too-frequent burning is one of the main causes of its increase. Harrington (1974) found that a late burn in the long dry season (usually late August in Uganda) carried out every third year reduced the biomass of C. nardus and encouraged the somewhat better, associated grasses of Brachiaria decumbens, Themeda triandra and Hyparrhenia filipendula. The burn should be against the wind and in weather which would minimize fire temperatures. This would prune the undesirable associated shrub Acacia hockii. Annual burning reduces the size of the C. nardus plants, but does not improve the sward.

Ability to compete with weeds

It is very competitive, and where overgrazing takes place in useful pastures it tends to increase.

Palatability

The grass is unpalatable to cattle and cattle have been known to die of starvation when an abundance of it, in green condition, was available (Harrington, 1974). Buffalo will eat it sparingly and elephants will accept it during the dry season (Field, 1971).

Chemical analysis and digestibility

Its feeding value is low.

Control

In addition to a late burn in the long dry season, van Rensburg (1971) showed that, during the wet season, a soil tillage treatment combined with the sowing of E. curvula at 2.64 kg/ha revegetated severely damaged Themeda/Cymbopogon veld and increased dry-matter production. Hand hoeing is the most effective method of elimination where labour is not expensive.

Natural habitat

Common in grassland and open woodland of Acacia and Combretum on the hills in Uganda.

Genetics and reproduction

2n=20 (Fedorov, 1974).

Economics

Cymbopogon nardus is an unpalatable, unwanted invader of Ankole district pastures in Uganda. Removal of C. nardus from fully stocked pastures improved growth rates by about 30 percent, but the rate of recolonization can be extremely rapid. The knowledge of the ecology of the grass is supremely important in the development of the area (Harrington, 1974). It is a good thatching and mulching material, and the grass produces citronella!, an aromatic oil.

Animal production

The invasion of a pasture by C. nardus always leads to a reduction in animal production.

Further reading

Harrington, 1974; Harrington & Pratchett, 1974b.