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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.
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