Water Couch

Paspalum distichum L.

Synonyms - Paspalum paspalodes.

Family: Poaceae.

Names:

Paspalum is from the Greek paspalos meaning millet.
Water Couch because it is tolerant of moderately saline wet conditions and it is in the Couch genus.

Other names:

Salt Water Couch grass
Saltwater Couch
Sea shore Paspalum

Summary:

Water Couch is a perennial, coarse grass spreading by creeping, wiry runners with dark nodes. The inflorescence is of 2 or 3 (or rarely to 5) slender spreading branches each with 2 rows of small spikelets and each spikelet is 2.5-3.5 mm long. Native to tropical and subtropical areas of the world, it is a weed of wetter disturbed areas, cultivation, watercourses and wet pastures. It flowers in summer.

Description:

Cotyledons:

One

Leaves:

Blade - Parallel sided, 30-150 mm long x 1-8 mm wide, flat when fresh, often folded and keeled when dry. Hairless (except at mouth) or minutely hairy. Tip pointed. Edges often tend to roll inwards towards the top.
Ligule - Membranous, 0.5 mm long, flat or obtuse on top. A few hairs behind it.
Auricles - None.
Sheath - Keeled, often longer than the internode and overlap each other, become loose with age. Membranous edges. Rarely hairy on the edges.

Stems:

Long, spreading, creeping, stolons and occasionally rhizomes, root at nodes, tough, usually long and branching. Nodes dark. Hairless or a few hairs at the mouth. May float in shallow water. Stems bend upwards but less than 600 mm high.
Flower stem - 50-600 mm tall, erect or bending upwards from creeping stems.

Flower head:

Short stalk (peduncle) often hidden in top sheath. 2 or rarely 3-5 flattened spikes (racemes), 15-70 mm long, initially erect but spreading to almost horizontal and curving with age. The two racemes emerge from the top of the stalk and the third if present emerges lower down.

Flowers:

Spikelets - Oblong, 3-4.5 mm long x 1.5 mm wide, flattened on back, Usually single, occasionally paired near the middle of the raceme, overlapping. On short or no stalks (pedicels). In 2 rows on one side of the flattened rachis that is winged and 1-2 mm wide.
Florets -
Glumes - Lower one absent or a small scale. Upper one is the same length as the spikelet, 3-3.5 mm, 3-5 ribbed, conspicuous midrib. Thinly membranous. Tiny low lying hairs or hairless.
Palea -
Lemma - Upper lemma empty, 5-7 nerved and hairless. Lower one the same length as the spikelet, 3-3.5 mm long, fertile, smooth, 3-5 ribbed, conspicuous midrib, thinly membranous to somewhat leathery and hairless.
Stamens -
Anthers - Oblong, purple and stick out of the spikelet.

Fruit:

In spikelet.

Seeds:

Enclosed in fruit.

Roots:

Fibrous roots and long, creeping stolons and occasionally rhizomes.

Key Characters:

Panicle of 2 (rarely 3-4) flattened spikes, 20-50 mm long. Spikelets solitary or in two rows, shortly pedicellate, margins not fringed. Upper glume minutely appressed-hairy or glabrous.

Biology:

Life cycle:

Perennial. Flowers December to April.

Physiology:

Tolerant of moderately saline areas.
Frost sensitive.

Reproduction:

By seeds and stem fragments.

Flowering times:

Throughout the year in SA.
December to April in Perth.
Summer in WA.

Seed Biology and Germination:

Seed is sterile on some varieties and abundant and viable on others.

Vegetative Propagules:

Stem fragments, rhizomes and stolons.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Spread rapidly by stem fragments in water. The seed is an important form of dispersal in some varieties that produce large amounts of seed. On other varieties all the seed is sterile.

Origin and History:

Cosmopolitan in warm temperate and tropical regions.
Possibly native to northern Australia.

Distribution:

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

Courtesy Australia's Virtual Herbarium.

Habitats:

Damp, wet and waterlogged areas.
Often abundant near brackish rivers.

Climate:

Tropical. Temperate. Mediterranean.

Soil:

Plant Associations:

Significance:

Beneficial:

Fodder.
Lawn grass.

Detrimental:

Weed of water ways, crops, cultivation, fallows, orchards, vineyards, lawns, vegetables, drainage channels and disturbed areas.

Toxicity:

Paspalum staggers cause by a fungal ergot (Claviceps paspali) produced in the seed. It appears as a dark sticky exudate initially then turns into rounded bodies (sclerotia) about 3 mm long, yellowish-grey, dry and firm. The grass is toxic when the sclerotia are present from February to April.
Cattle are most commonly affected with fewer reports of problems with sheep and horses.
Occasionally may cause illness in children who chew the seed heads.
Sticky exudate can cause dermatitis in humans and stain clothing.

Symptoms:

Excitement, distrust, tendency to charge, trembling, stilted gait, staggers, loss of muscle control, exaggerated bending of front legs if forced to run, may lose balance and drop suddenly if startled, frothing at the mouth, discharge from nostrils and eyes, increased heart rate, reddening of skin, soreness of muzzle, feet and teats, fall down with tetanic spasms, teeth grinding and occasional violent kicking. Animals usually die by misadventure or drowning in waterholes rather than direct toxicity.

Treatment:

Remove stock quietly from infected paddocks if in the early stages of poisoning. Recovery usually takes a few days. In the later stages of poisoning moving stock may bring on more serious symptoms.
Treatment with 350-400 g Epsom salts is occasionally suggested.
Graze paddocks heavily next season, mow or 'Spray Top' to reduce seed head formation.

Legislation:

None.

Management and Control:

Heavy grazing provides a degree of control.
It is very tolerant of mowing.
Multiple low doses of glyphosate about 4 weeks apart when the Couch is actively growing is the cheapest method of control and far more effective than a single large dose.
In cropping areas, Water 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 800 mL/ha glyphosate(450g/L) followed by 800 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 2 L/ha glyphosate(450g/L). Rates should be adjusted so that a total of 3-4 L/ha glyphosate is applied over the 2-4 sprays. This will give results similar to applying 6 L/ha as a single application. Cultivation, 2-10 days after spraying with a scarifier or using a tyned full cut seeder to plant the crop will provide improved control compared to minimum tillage planting.

Thresholds:

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 is 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:

Related plants:

Paspalum (Paspalum dilatatum)
Plicatulum (Paspalum plicatulum)
Russell River grass (Paspalum paniculatum)
Saltwater Couch (Paspalum vaginatum)
Scrobic (Paspalum scrobiculatum)
Sourgrass (Paspalum conjugatum)

Plants of similar appearance:

Grasses.
Other Couch Grasses include:
Couch (Cynodon dactylon) a softer grass with narrower leaves and the inflorescence is a whorl of radiating branches with 1-3 mm long spikelets.
English Couch (Elytrigia repens) a slightly rough grass with similar broad leaves. The inflorescence is an erect spike with larger, 8-17 mm long, alternate spikelets

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P51-52. Diagram.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P227.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P63.

Ciba Geigy (1980) Grass Weeds 1. CIBA GEIGY Ltd, Basle, Switzerland. P108. Diagrams.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P337.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P62. Photo.

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). #938.4.

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). P973.

Paterson, J.G. (1977). Grasses in South Western Australia. (Western Australian Department of Agriculture Bulletin 4007). P69. Diagram.

Acknowledgments:

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