Couch

Cynodon dactylon (L.) Pers.

Synonyms - Capriola dactylon

Family: Poaceae.

Names:

Cynodon is from the Greek kynodon, meaning dogs tooth, or from a translation of the French name for this plant chiedent.
Couch

Other names:

African Star Grass
Bermuda grass
Common Couch
Creeping Finger Grass
Devil Grass
Doub Grass
Giant Star Grass
Green Couch
Indian Couch
Indian Daub Grass
Star Grass
Swamp Couch

Summary:

A spreading, mat forming, wiry stemmed perennial grass with small, flat, soft leaves, stolons, rhizomes and a 3-7 fingered seed head with 2 rows of 1-3 mm long spikelets.

Description:

Cotyledons:

One.

Leaves:

Parallel veins. Alternate, regularly arranged in 2 opposite rows. Hairless apart from a few at the base. Emerging blade folded in the shoot.
Blade - Green to greyish green or bluish green, flat or folded, parallel sided to lance shaped, 10-160 mm long x 1-5 mm wide, ribbed, edges rough to touch, sometimes stiff. Tapers to a pointed tip Hairless or sparsely hairy on the upper surface. Occasionally has hairs at the mouth.
Ligule - 0.2-0.3 mm long, rim of hairs (bearded).
Auricles - None.
Sheath - Leathery with papery edges. May have hairs on lower part. Initially tight, becoming loose with age. Tubular at base.

Stems:

Solid, wiry, creeping, prostrate, up to 2000 mm long and 300 mm high, branching stolons with roots and flowering stems at the nodes, and underground, tough, scaly rhizomes. Rarely kneed at the nodes.
Flower stem - Erect or occasionally prostrate.

Flower head:

Terminal umbel of 2-7 finger like spikes at the end of the vertical flowering stem in an umbrella form. Spikes are parallel sided, 20-100 mm long, straight or curved, initially green and turning purplish or red brown with age. Spikelets alternate, overlapping, angled in 2 rows along on underside of the flattened or triangular, slender branch axis(rachis). Main axis of the spikelet (rachilla) extends beyond the floret ending in a slender bristle.

Flowers:

Spikelets - 2-3 mm long, broad, flattened, 1 fertile flower, small, no stalk. Breaks above the glumes.
Florets - Bisexual. Looks fringed due to palea hairs.
Glumes - 2, 1-1.5 mm long, narrow egg shaped. Lower glume 1 nerved, upper glume 1-3 nerved, with rough thickened keel. Tip pointed. Hairless. Remain on the spike axis.
Palea - Narrow,1.5-2.5 mm long, rough to touch. Hairs along the nerves.
Lemma - Purplish or lead grey, single, boat shaped, membranous, 1.5-2.5 mm long, membranous, folded, 3 nerved, awnless, tiny white hairs on the keel. Acute or obtuse tip.
Stamens -
Anthers -

Seeds:

Sub cylindrical, flattened, smooth and hairless, less than 1 mm long.

Roots:

Tough scaly underground rhizome with fine roots. Fine roots at the nodes of above ground stolons.

Key Characters:

Biology:

Life cycle:

Perennial grass. Up to 300 mm tall. Germinates from summer to autumn. Flowers mainly in late-winter to spring

Physiology:

Sensitive to frost.
Drought tolerant.

Reproduction:

By seed, rhizomes, stolons and stem fragments.

Flowering times:

All year in SA.
Mainly summer to autumn in NSW.
October to November in Perth.
Spring and summer in WA.

Seed Biology and Germination:

Viable seed appears to come from late summer to early autumn flowers.
Seed germinates readily after scarification.
Requires high temperatures for germination.

Vegetative Propagules:

Rhizomes and stolons.

Hybrids:

Many forms and hybrids.
At least 3 forms in Australia.
1) Naturalised varieties are small leaved, branched, sward forming grasses.
2) Imported turf varieties that are small leaved, sparingly branched, sward forming grasses.
3) Imported pastures varieties are larger leaved, many branched, spreading grasses.

Allelopathy:

Produces toxins that affect the growth of companion species.

Population Dynamics and Dispersal:

Spread by seed, expansion of the rhizome and stolons and stem fragments moved by cultivation.

Origin and History:

Cosmopolitan.
Native to the tropics and the Kimberly region of WA.

Distribution:

ACT, NSW, NT, QLD, SA, TAS, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Warm topical, subtropical and temperate.

Soil:

Prefers sandy summer moist soils and flats that occasionally flood.
Occurs on a wide range of soil types from sands to heavy clays.

Plant Associations:

Significance:

Beneficial:

Very common lawn grass.
Fodder, pasture grass.
Shelter.
Soil stabiliser.

Detrimental:

One of the most serious weeds of world agriculture.
A weed of more than 40 crops, pastures, vineyards, orchards, and horticulture causing yield reductions.
Weed of irrigation channels, stream banks, roadsides, wetlands and river banks.
Difficult to control and several sprays are usually required.

Toxicity:

Some forms may cause HCN (Prussic acid) poisoning, but this is rare in Australia. It only occurs under certain growth conditions, which are poorly defined. Sheep and cattle are most commonly affected. Most cases involve hungry stock exposed to lush couch growth from December to March after summer rains.

Symptoms:

Trembling, frothing at the mouth, rapid breathing, blueness of gums, apathy.

Treatment:

Remove stock from infestation. Treat as for HCN poisoning.

Legislation:

None.

Management and Control:

In cropping areas, Couch can usually be reduced to insignificant levels by using glyphosate for spray topping, summer weed control and pre plant weed control.
A typical program would be heavy autumn grazing followed by heavy grazing in late winter to spring with stock being removed when the annual grasses start to elongate in spring. When the heads of annual grasses just start to emerge Spraytop with 1200 mL/ha glyphosate(450g/L) followed by 1200 mL/ha 4 weeks later. If summer weeds emerge then spray with glyphosate at a rate appropriate for the weeds. In autumn spray annual weeds when they have reached the 2 leaf stage with about 4 L/ha glyphosate(450g/L). Rates should be adjusted so that a total of 6-8 L/ha glyphosate is applied over the 2-4 sprays. This will give results similar to applying 9 L/ha as a single application. Cultivation, 2-10 days after spraying with a blade plough or scarifier and using a tyned full cut seeder to plant the crop will provide improved control compared to minimum tillage planting.
Burning, cultivation or grazing alone are generally ineffective but may improve the effectiveness of herbicide treatments.

Thresholds:

Low levels can often lead to significant crop yield reductions due to direct competition for nitrogen and consumption of early season or carryover moisture.
Dense stands can be allelopathic or release chemicals into the soil that reduce the germination and growth of crops.
Forms patches that tend to exclude most other species.

Eradication strategies:

Burn the grass to reduce thatch and encourage young growth ready for spraying.
Avoid dumping garden refuse containing these grasses in areas where they may establish. Manual control is very difficult and mowing or burning are usually ineffective. Repeated cultivation can provide control. Solarisation can be useful in organic areas.
Herbicides provide the most reliable control.
100 mL glyphosate(450g/L) plus 25 mL Pulse® in 10 L of water applied when the grass is actively growing every 8 weeks over the spring to autumn period or whenever fresh growth is 20-50 mm tall is the most effective control. For broad acre spraying use 6 L/ha glyphosate(450g/L).
Selective control amongst broad leaved plants can usually be achieved by spraying with 800 mL/ha Verdict®520 or 4 L/ha quizalofop(100g/L) or 6.4 L/ha Fusilade®Forte plus 1% spray oil. Use 16 mL Verdict®520 or 80 mL quizalofop(100g/L) or 125 mL Fusilade®Forte plus 100 mL of spray oil per 10 L water for hand sprays.
Painting runners or crowns with 1 L glyphosate in 2 L water is useful in sensitive areas.
It normally takes 2-3 years of vigilant control to achieve eradication from an area.

Herbicide resistance:

Biological Control:

Unlikely to be introduced because some varieties are native plants.

Related plants:

Bermuda Grass (C. nlemfuensis)
Blue Couch (C. incompletus) has a membranous ligule with a hairy tuft, it rarely has rhizomes and the rachilla is shorter than the floret.
C. arcuatus
C. transvaalensis has a very narrow leaf blade, less than 1 mm wide and 1-3 spikes in each head.

Plants of similar appearance:

Perennial grasses.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P43. Photo.

Black, J.M. (1978). Flora of South Australia. (Government Printer, Adelaide, South Australia). P206. Diagram.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P59-60. Diagram.

Ciba Geigy (1981) Grass Weeds 2. CIBA GEIGY Ltd, Basle, Switzerland. P53. Diagrams.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P78. Photo.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P308-309.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #400.2.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P949.

McBarron, E.J. (1983). Poisonous plants. (Inkata Press, Melbourne). P8. Diagram.

Paterson, J.G. (1977). Grasses in South Western Australia. (Western Australian Department of Agriculture Bulletin 4007). P40.

Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). P25. Diagrams. Photo.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.