Dichanthium sericeum


Scientific name

Dichanthium sericeum (R. Br.) A. Camus

Subordinate taxa:
Dichanthium sericeum (R. Br.) A. Camus subsp. sericeum
Dichanthium sericeum (R. Br.) A. Camus subsp. humilius (J.M. Black) B.K. Simon
Dichanthium sericeum (R. Br.) A. Camus subsp. polystachyum (Benth.)

Synonyms

Dichanthium affine (R. Br.) A. Camus
Andropogon affinis R. Br.
Andropogon sericeus R. Br.

Family/tribe

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

Common names

D. sericeum subsp. sericeum - Queensland Blue grass , slender bluegrass.
D. sericeum subsp. humilius - annual bluegrass.
D. sericeum subsp. polystachyum - tassel bluegrass (Australia):  silky bluegrass (USA).

Morphological description

A tufted, erect perennial, 30–80 cm tall, generally rather slender.  Tufts never very large, generally 10–15 cm diameter and with a fairly weak root system.  Culms are densely branched at the base and often from the upper nodes.  The stems are smooth and hairless but the nodes bear a ring of long (1.5 mm) erect white hairs.  Leaves are flat, 8–15 cm long, 2–4 mm wide, often bluish-purple, typically without hairs although some forms are hairy.  Leaf sheaths are round, close to the stem and may be almost as long as the internodes.  Short ligules are membranous and ragged.
The inflorescences generally have 2–4 stalkless erect racemes with paired spikelets crowded into 2 ranks.  The upper pairs, with a fertile sessile spikelet and a sterile pedicellate one, are all densely hairy, giving a silky-hairy appearance to the inflorescence.  The lemmas of the upper sterile florets have a brownish, twisted hydroscopic awn about 2.5 cm long.  Old culms often bear a remnant white tuft of seed head on the tip.

D. sericuem subsp. sericeum is more robust than subsp. humilius which is found in the drier regions as an annual .
D. sericeum subsp. polystachyum generally has more than 10 racemes, all densely hairy.

Dichanthium sericeum is a complex of many ecotypes that have sometimes been grouped in four types based on colour and hairiness (blue or green, hairy or glaucous ).

Distribution

Native to:
Malesia:  Papua New Guinea.
Australia:  New South Wales, Northern Territory, Queensland, South Australia, Victoria, Western Australia.
More common in the tropical and subtropical regions on heavier black clays (bluegrass downs).
Tassell bluegrass (D. sericeum subsp. polystachyum) is more common on the lower fertility black soils of the monsoonal regions of northern Australia.

It has naturalised in parts of the southern United States.  Probable distribution from 30°N to 32°S.

Uses/applications

Very good quality natural grazing on heavier and more fertile black soils.  However, in Queensland, many of these soils are also suitable for cropping and bluegrass native pastures remain only on non-arable landscapes in the bluegrass downs of southern and central Queensland and after a sequence of good rainfall years as a component of some Mitchell grass (Astrebla spp.) downs pasture in the more arid western regions, often more abundant on lightly grazed pastures such as on roadsides.  Makes soft hay.  Tassell bluegrass is baled for hay in the bluegrass-browntop (Eulalia fulva) pastures of the Gulf region of Queensland.
While a soft palatable grass with slender stems when mature, it is easily uprooted during dry conditions leading to loss of plants.

Ecology

Soil requirements

Grows best on fertile, heavy black clays (vertisols) of neutral to alkaline pH .

Moisture

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Bluegrass downs are found in the 500–700 mm rainfall zone with tassel bluegrass in monsoonal regions.  Tolerates saturated clays;  tassel bluegrass tolerates poorer fertility and seasonal waterlogging.  Reasonable drought tolerance but less so than Mitchell grass (Astrebla spp.).

Temperature

Summer growing but also reasonable growth in the cooler conditions of spring and autumn if moisture is available.  Frost tolerance claimed as moderate to poor.

Light

Intolerant of shade.

Reproductive development

Probably short-day response as it flowers in February to May in Queensland.

Defoliation

Tolerant of moderate grazing.  However, cattle and sheep, and especially horses, will pull the plant out by the roots allowing less palatable grasses to increase.

Fire

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Tolerates moderate intensity fires and recovers from seed buried in soil.

Agronomy

Establishment

The natural areas of Queensland bluegrass are self-regenerating, establishing very readily from seed.  However, it can be slow to bulk up naturally on abandoned run-down cropping lands due to competition from annual grasses and broadleaf weeds and lack of soil seed supply.
Not all seed will establish immediately when wetted which prevents loss of soil seed reserves, while partially germinated seed can return to dormancy (hydropedesis) when exposed to moisture stress during germination.  These seeds will survive and resume germination when moisture becomes available.
Where commercial seed is available, it can be difficult to spread because the fluffy awned seed does not flow through conventional machinery.  De-awning and/or pelleting may improve flow.

Fertiliser

Generally low requirement for plant nutrients with production usually limited by moisture stress.  Suitable basaltic soils rarely need additional phosphorus but some nitrogen could be beneficial when renovating run-down cropping land.  Sulphur may be deficient on some basaltic soils.

Compatibility (with other species)

Associated with a range of native species on the bluegrass downs of eastern Australia including species of Bothriochloa, Panicum, Digitaria and Chloris and temperate grasses such as Stipa and Danthonia in the southern downs and with Eulalia and Iseilema spp. in the northern monsoonal regions.
May be difficult to maintain with other more vigorous introduced species because it is highly palatable and preferentially grazed.

Companion species

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Legumes:  Annual medics (Medicago truncatula) in regions with sufficient winter rainfall .  May be found with native legumes such as Rhynchosia minima.

Pests and diseases

No information available.

Ability to spread

Spreads through wind disposal of fluffy seed and on animal coats and in mud on hoofs.

Weed potential

Valuable native grass under threat from cropping.

Feeding value

Nutritive value

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Good quality feed with up to 10% CP, 0.2% P and 62% digestibility.  Quality drops quickly after maturity (10% CP drops to 4–6%) to become very low (2%) during the winter dry season.

Palatability/acceptability

Very palatable while green, and slender stems are more digestible than coarser grasses when pastures are mature.

Toxicity

None reported.

Production potential

Dry matter

Yields are dependent on soils and climate and because of it’s distribution range (see “Distribution” above), can vary from 1.5–9.0 t/ha.

Animal production

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The carrying capacity of bluegrass pastures is about one beast on 5 ha in the 600–700 mm rainfall areas of the Darling Downs of southern Queensland, Australia.  Higher grazing pressure results in the loss of bluegrass.

Genetics/breeding

2n = 20.  Sexually reproducing diploids, possibly changing from apomictic to sexual reproduction as temperatures and photoperiod change in late summer.

Seed production

Heavy seeding species that can be harvested using commercial brush harvesters.  Seed yield 50–100 kg/ha.  Seed shows post-harvest dormancy but with maximum germination within 12 months.

Herbicide effects

Tolerant of atrazine.

Strengths

  • High quality grass .
  • Early spring growth.

Limitations

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  • Limited to fertile heavier soils.
  • Declines under heavy grazing.

Other comments

  

Selected references

Burrows, W.H., Scanlan, J.C. and Rutherford, M.T. (1988) Native pastures in Queensland: The resources and their management. Department of Primary Industries, Brisbane,

Queensland.Coleman, S.W., Taliaferro, C.M., Tyrl, R.J. 2004. Old World Bluestems. (Warm Season Grasses). pp. 906 - 936. 
Jacobsen C.N. (1981) A review of the species of Dichanthium native to Australia with special reference to their occurrence in Queensland. Tropical Grasslands, 15, 84–95.
Milson, J.A. (2000) Pasture plants of north-west Queensland. QI00015. Department of Primary Industries, Brisbane, Australia.
Tothill, J.C. and Gillies, C. (1992) The pasture lands of northern Australia: their condition, productivity and sustainability. Tropical Grassland Society of Australia Occasional Publication No.5. Brisbane, Australia.
Tothill, J.C. and Hacker, J.B. (1983) The Grasses of Southern Queensland. pp. 186–188. (The Tropical Grassland Society of Australia, Brisbane, Queensland).

Internet links

Cultivars

Cultivars

Country/date released

Details

‘Scatta’ Pending release in Australia.   

Promising accessions

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Promising accessions

Country

Details

ES-100, ES-200 Australia Tall and moderately tall, respectively.