Digitaria didactyla


Scientific name

Digitaria didactyla Willd.
Digitaria swazilandensis Stent

Synonyms

  

Family/tribe

Family: Poaceae (alt. Gramineae) subfamily: Panicoideae tribe: Paniceae.

Common names

D. didactyla :
Queensland blue couch, blue couch grass (Australia);  blue serangoon grass, green serangoon grass (Malaysia);  petit gazon (Mauritius).
D swazilandensis:
Swazi grass (Australia).

Morphological description

Small, strongly stoloniferous perennial grass with bluish coloured leaves.  Narrow leaf blades up to 3 cm long and 5 mm wide with a fine setaceous tip, sward can grow to 20 cm high with very dense leaf if not grazed.
Inflorescence usually two racemes, conjugate and sessile .

Differs from green couch (Cynodon dactylon ) in its shorter, broader leaf and its distinctive bluish colour.  Swazi cultivars are intermediate in colour between Queensland blue and green couch.  Swazi grass is coarser in the leaf and produces more bulk than Queensland blue couch.

Distribution

Native to:
Africa:  Malawi, Mozambique, South Africa (Natal, Transvaal), Swaziland.
Indian Ocean:  Mauritius, Reunion.

Now widespread through the tropics and subtropics (often under communal grazing or as a lawn grass ).  Swazi originates from southern Africa and has limited spread because it has been primarily propagated by stolons.

Uses/applications

Permanent pasture and turf grass.  As a pasture grass, it has invaded native pastures under heavy grazing pressure, generally on lighter sandy soils.  Withstands heavy grazing by horses.  As a lawn or golf course grass, it is generally laid as turf.  Some use as ground cover in higher rainfall areas.

Ecology

Soil requirements

Fairly wide tolerance but definite preference for lighter soils.  Very common on granitic sands.  Tolerant of low nutrient levels and moderately low pH but not with high Al.  Swazi grass has some degree of salt tolerance.

Moisture

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900–1,800 mm AAR, survives seasonal dry conditions and drought by losing all leaf.  On light soils, responds almost instantly to good rainfall .  Can tolerate short-term flooding.

Temperature

Warm season growth (>15°C) in the subtropics or higher altitude tropics.  Leaf shrivels when frosted.

Light

Tolerates some shade

Reproductive development

  

Defoliation

Very resistant to heavy grazing.  Normally invades native pastures of tussock species, e.g. Heteropogon contortus , under prolonged heavy grazing.  Not cut for feed due to low creeping growth, but excellent turf grass under regular mowing.

Fire

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Not generally burned due to light fuel loads under heavy grazing, but will recover quickly.

Agronomy

Establishment

Seed is available for lawns but is expensive so it is usually planted as turf.  Natural spread through cattle faeces under prolonged heavy grazing.  Swazi grass is a shy seeder.

Fertiliser

Pure swards of blue couch are not normally fertilised and have resulted from overgrazing of native tussock species.  However, it will respond well to N, and to associated legumes when fertilised with P.

Compatibility (with other species)

Under heavy grazing, combines well with creeping and other native and introduced legumes, especially if superphosphate is applied.

Companion species

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Legumes:  Desmodium triflorum , Zornia maculata, Glycine spp., Arachis pintoi , Aeschynomene falcata , Stylosanthes guianensis , Lotononis bainesii , Chamaecrista rotundifolia and white clover (Trifolium repens).

Pests and diseases

Patches of grey mould often seen in spring and autumn.  Can be attacked by spider mites (Oligonychus spp.).  Can be infected by Digitaria striate mosaic monogeminivirus.  Not infected by pangola stunt virus (unlike many other Digitaria spp.).  Swazi grass is less affected by moulds and other diseases than Queensland blue couch.

Ability to spread

Spreads rapidly by runners and seed.  Invades native pastures under persistent heavy grazing especially after legume introduction.  Seed reserves can be high in the soil;  germinable seed can be spread through dung of cattle on well grazed pastures (up to 20 germinable seeds/g faecal DM).

Weed potential

Stoloniferous (not rhizomatous ) and easy to kill (cf. green couch Cynodon dactylon ).

Feeding value

Nutritive value

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No information available.

Palatability/acceptability

Very palatable.

Toxicity

None reported.

Production potential

Dry matter

Up to 11 t/ha DM recorded with fertilizer application of 225 kg/ha N.

Animal production

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Under heavy grazing, about 90 kg/head/year due to low bulk.

Genetics/breeding

2n = 18, 36.

Seed production

Seed harvest is difficult due to low growth.  In south-east Queensland (Australia), yields of 100 kg/ha seed have been recorded in 2 harvests in January and November respectively.  Seed remained viable (with germination up to 80%) over 2 years when stored at 15°C.  Dehulling seed damaged germination and could damage the caryopses.

Herbicide effects

  

Strengths

  • Very resistant to heavy grazing.
  • Invades overgrazed native plants maintaining ground cover.
  • Palatable.

Limitations

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  • Low production.
  • Leaf shrivels under drought and frost conditions.

Other comments

  

Selected references

  

Internet links

Cultivars

Cultivars

Country/date released

Details

‘Aussieblue’ Australia, 1997 Useful for lawn turf having vigorous lateral spread, wide leaf and sparse flowering.

Promising accessions

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Promising accessions

Country

Details

CPI 40674, CPI 40676 New South Wales, Australia Reported to be collected in Africa by Tony O’Brien in 1969-70.  Both lines produce viable seed, CPI 40674 more than CPI 40676.  Work at Grafton under way to select a commercial line of 40674.  Both lines produce more bulk than Queensland blue couch and have coarser leaves