Giant Reed

Arundo donax L.

Family: Poaceae

Names:

Other Names:

Bamboo

Summary:

Giant Reed is a very large, bamboo-like, rhizomatous grass growing in large clumps with many stems to 8 m high in semi aquatic environments. It is one of the largest grasses in the world and has woody stems bearing evenly spaced leaves in two rows. The 2 rows of evenly spaced leaves are 20-75 cm long and 4-8 cm wide with rough margins. The pale or whitish inflorescence is plume-like, feathery and 30-60 cm long at the ends of the stems. The spikelets are 8-16 mm long and have 2-7 florets. The outer segment (lemma) of each floret is silky hairy and tapers to a 2-lobed tip with a slender bristle (awn) between the lobes. Giant Reed is native to southern Europe and Asia and was introduced as a garden plant or windbreak, but is now a weed along watercourses, freshwater wetlands and in moist disturbed areas. It flowers in autumn and winter. It is often incorrectly call Bamboo.

Description:

Cotyledons:

Two.

First leaves:

Leaves:

Alternate. Emerging leaf rolled in the bud.
Green (or variegated in the versicolor variety).
Evenly spaced in 2 rows along the stem.
Blade - Green, flat, 200-750 mm long x 40-80 mm wide with rough edges. Linear to lance shaped. Hairless.
Ligule - membranous, very short, fringed.
Auricles - None, but the blade does continue around the collar a little and often has a few hairs.
Sheath - clasps the stem. Sometimes with hairs on the lower leaves. Edges hairless.

Stems:

Many arising from rhizomes, Bamboo like, stout, 2-8 m tall, almost woody. Rarely branching. Tufted. Hairless.

Flower head:

Erect, large, feathery, plume like, densely branched, 300-600 mm long x up to 100 mm wide, at the ends of stems. The main axis (rachis) and branches (rachilla) are smooth and hairless.

Flowers:

Spikelets - 8-16 mm long and single on short stalks. 2-7 flowered.
Florets - 2-7, bisexual, successively smaller from the base to the tip of the spikelet. Tip floret is usually empty.
Glumes - 8-13 mm long, narrow, keeled, 3-5 ribbed, pointed tip. Inner and outer glume almost the same size. Hairless.
Palea - Shorter than lemma, translucent, 2 keeled, flat tipped, Fine hairs on the edges and tip.
Lemma - Thin, wider than the glumes, 10-12 mm long, softly hairy, Tapering to the tip. 3-9 ribbed with 2 ribs forming slender lobes on either side of a straight, 3 mm long awn. Hairy on the back
Stamens -
Anthers -

Fruit:

Breaks above the glumes and between the florets at maturity.

Seeds:

Oblong, free and enclosed by palea and lemma.

Roots:

Branching, thick, tuberous rhizomes and many fine roots.

Key Characters:

Tall grass more than 2 m high with a plume like panicle more than 300 mm tall.
Leaves in 2 rows along culms. Veins parallel.
Rachilla joints bearing long silky hairs enveloping the lemma
Spikelets pedicellate with 2 or more bisexual florets.
Spikelets breaking at maturity above the more or less persistent glumes.
Lemma bearing long silky hairs.
Adapted from E.M. Bennett and T.D. Macfarlane Flora of Perth

Biology:

Life cycle:

Perennial. Rhizome or stem fragments form roots and build up a tuberous rhizome. Stems or culms emerge in spring and form seed heads in late summer. The seeds are usually sterile and don't germinate.

Physiology:

It can survive summer drought if subsoil moisture is available.

Reproduction:

Mainly by rhizome spread and fallen canes taking root.

Flowering times:

April to June in Perth.

Seed Biology and Germination:

Seeds appear to be sterile.

Vegetative Propagules:

Tuberous rhizome and fallen canes or stem fragments.

Hybrids:

A variegated variety (var. versicolor) occurs near Perth.

Allelopathy:

Population Dynamics and Dispersal:

It spreads by intentional planting and discarded or water transported stem and rhizome fragments that transplant easily. Within a patch it spreads vegetatively by it tuberous rhizome and falling canes forming thickets.

Origin and History:

Native to the Mediterranean, southern Europe and Asia, Madagascar and India.
Introduced intentionally in most situations as a windbreak or shelter.

Distribution:

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

Courtesy Australia's Virtual Herbarium.

Habitats:

Wet areas.

Climate:

Temperate.

Soil:

Prefers freshwater areas.

Plant Associations:

Tends to form mono-specific stands.

Significance:

Beneficial:

Fodder. Windbreak. Soil stabiliser. Fibre. Ornamental. Thatch for rooves.
Stems used for paper pulp and reeds for musical instruments such as the clarinet and bassoon.

Detrimental:

Weed. Highly flammable and resprouts quickly after burning.
Forms dense inpenetrable thickets. Single clones can cover hundreds of hectares.
Weed of water courses and fresh wet areas
Invasive weed of the USA threatening native riparian habitats.

Toxicity:

Not recorded as toxic.

Legislation:

Noxious weed of NSW.
Cultivated in VIC.

Management and Control:

Avoid dumping garden refuse containing stems and rhizomes in wet areas where they may establish. Manual control is usually difficult because all the rhizome must be removed otherwise small fragments of root and stem re shoot. 100 mL glyphosate(450g/L) plus 25 mL Pulse® in 10 L of water applied when the reed is actively growing is the most effective control. Repeat every 12 weeks or when regrowth reaches about 20 cm tall. Mowing and grazing are usually effective if continued over a few years. Burning is more variable but useful in reducing the top growth and making it easier to apply herbicides. Selective control amongst broad leaved plants can usually be achieved by spraying with 5 L/ha Verdict®520 plus 1% spray oil. Use 50 mL Verdict®520 plus 100 mL of spray oil per 10 L water for hand sprays and spray until just wet. This will control the reed with little effect on broad-leaved companion plants.

Thresholds:

Eradication strategies:

Start at the top of the catchment, otherwise fragments in water flows will reinfest the treated areas. Spray with 1 litre of glyphosate in 100 litres of water. The best time to spray is just after flowering. Dense areas can be burnt first, to allow easier access, then the regrowth sprayed with glyphosate when it is 250-500 mm tall.
In areas where desirable broad-leaved species are intermixed with the Giant Reed, many of the grass selective, group A herbicides, will provide selective control. Use 2 L of fluazifop212 or 500 mL Verdict®520 plus 1 litre of spray oil in 100 litres of water and spray until just wet, just after flowering. Repeat when regrowth reaches 200 mm tall and is actively growing.

Herbicide resistance:

Biological Control:

Related plants:

None.

Plants of similar appearance:

Bamboo (Arundinaria spp. Bambusa spp. and Phyllostachys spp.) has a stalk like constriction at the base of the leaf.
Common Reed (Phragmites australis) has a brownish inflorescence with more numerous silky hairs on the spikelets and is usually smaller and found growing in shallow water.
Pampas Grass (Cortaderia spp.) has it leaves arising from the base rather than along the stem.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P37. Photos.

Bodkin, F. (1986). Encyclopaedia Botanica. (Angus and Robertson, Australia).

Ciba Geigy (1981) Grass Weeds 2. CIBA GEIGY Ltd, Basle, Switzerland. P22. Diagrams.

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

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). P42. Photo.

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

Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). 105.1.

Paterson, J.G. (1977). Grasses in South Western Australia. (Western Australian Department of Agriculture Bulletin 4007). P28. Diagram.

Marchant et al (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P940.

Randall, J.M. and Marinelli, J. (1996) Invasive Plants. (Brooklyn Botanic Gardens Inc. Brooklyn) P84. Photo.

Acknowledgments:

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