Onion weed

Asphodelus fistulosus L.

Synonyms - Asphodelus tenuifolius.

Family: - Liliaceae.

Names:

Asphodelus is from Greek meaning 'head of a pike' and refers to the appearance of some plants in the lily family.
Fistulosus is from the Latin fistula meaning tube and refers to the hollow leaves.
Onion weed refers to its weedy nature and leaves that resemble onion leaves. It does not have a bulb or smell like onion.

Other Names:

Asphodel (NZ)refers to the genus name.
Hollow-stemmed Asphodel (Europe)
Wild onion

Summary:

Onion Weed is a hairless, tufted herb with hollow, somewhat succulent cylindrical leaves that are 180-400 mm long. The erect flowering stem is also hollow and may be up to 600 mm tall and branched with many small flowers. The flowers have 6 white (or pinkish) petals, 7-12 mm long and each petal has a brownish or purplish central stripe. There are 6 stamens with dark brown anthers and a slender style which is minutely 3-lobed at the tip. It looks like an onion but has no bulb and no onion odour.
Native from southern Europe to India, it is a weed of roadsides and railway verges, but is invading nearby bushland, particularly in drier areas and on alkaline soils. It is a common roadside weed from Albany to Esperance and north to Kojonup and flowers in winter and spring.

Description:

Cotyledons:

One.

First leaves:

Round. Hollow. Thin. Hairless. Tip pointed. Seed case often stuck to tip.

Leaves:

Many attached spirally at base. Shorter than flowering stems.
Blade - Hollow cylindrical (with one side flattened) leaves. Dark green to greyish green, usually striped. Hairless. 180-500mm x 1.5-4mm wide. Tip pointed.
Ligule - None
Auricles - None

Stems:

Main stem is very short and has leaves attached spirally.
Flowering stem - Hollow, erect, rigid, smooth, hairless. May branch above half way to the top. 200-800 mm tall.

Flower head:

Long racemes at the ends of stems. Flowering tip is initially compressed and elongates as flowering progresses. Flowers open sequentially from the base of the stem.

Flowers:

Alternate and fairly evenly spaced on the stem. Symmetric, single and more or less upright. On small jointed stalks with a bract at the base. 10-20 mm diameter. Buds pink.
Pistil - 3 carpels.
Ovary - 3 celled, with 2 side by side ovules. Style, thread like and 7 mm long.
Perianth - 2 whorls of 3 segments. Free. Elliptical. Blunt tip
'Petals' - 6 pink or white elliptical petals with a brown or purple central stripe. 5-10 mm long
Stamens - 6. White or cream. Filaments free.
Anthers - Orange

Fruit:

Almost globular, wrinkled seed capsule. 4-6 mm diameter. 3 segments that are notched near the top and crosswise wrinkled. 3-6 seeds (1-2 seeds in each segment).

Seeds:

Triangular. Black or brown. Surface hairless, dimpled and wrinkled. 3-4 mm long.

Roots:

Long, thick and fine, fibrous, yellow. No taproot.

Key Characters:

Biology:

Life cycle:

Annual, biennial or perennial. Germinates any time of the year with a flush in late summer to autumn. The seedlings grow slowly and usually take 18 months before flowering, but in some areas they act as annuals and flower in the same season then die. Older plants make their main growth over winter and flower from June to November. The flower stems and some leaves die with the onset of summer and produce new leaves and stems from the base of the plant in the following autumn.

Physiology:

Once established it is tolerant to drought.

Reproduction:

By seed.

Flowering times:

June to November but mainly August to October.

Seed Biology and Germination:

Seed remains viable in the soil for many years. It can germinate at any time of the year.

Vegetative Propagules:

It can re shoot from fragments spread by cultivation.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

It is mainly spread by dead plants bearing seeds blowing in the wind or entangling on stock or machinery. Seeds are also spread with soil movement and in water.
It rarely establishes in well managed perennial pastures.

Origin and History:

Southern Europe, Mediterranean, Asia minor, Western Asia to India.
It is only a minor weed in other parts of the world.
It was probably introduced as an ornamental and recorded from Melbourne in 1857 and Adelaide in 1858. It was found in the NT in 1974 and now occurs over large areas.

Distribution:

NSW, NT, QLD, SA, TAS, VIC, WA.
Occurs from Exmouth to Eucla in WA.
In Tasmania it is only in localised areas.

Courtesy Australia's Virtual Herbarium.

Habitats:

Tends to occur in disturbed or overgrazed areas.

Climate:

Semi arid to subhumid warm temperate.
Most abundant in areas with 250-500 mm annual rainfall.

Soil:

Prefers low fertility sands, gravels and alkaline soils, but occurs on a wide range of soils.

Plant Associations:

Significance:

Beneficial:

Provides pollen for bees.
Occasionally sold as an ornamental species.
Does not host Root Lesion Nematodes (Pratylenchus neglectus or thornei) 63

Detrimental:

A weed of crops and pastures causing yield reductions due to competition from established plants.
Unpalatable and not eaten by stock unless feed is extremely scarce.
Weed of roadsides and disturbed areas.
An invading species that is difficult to control once established.
Large plants entangle in both tine and disc cultivation equipment.
It is not expected to be a major environmental weed in ungrazed and undisturbed areas.

Toxicity:

Causes dermatitis in some people.
Sometimes reported to cause dermatitis in cattle but it is not likely.

Symptoms:

Dermatitis.

Treatment:

Remove stock from the infested areas.

Legislation:

Noxious weed of NSW, NT, SA, TAS, VIC.

Management and Control:

Don't overgraze pastures and avoid irregular cultivations.
Plant competitive pasture species and apply appropriate fertilisers.
Increase the level of cultivation. Onion weed is more prolific in zero tillage cropping systems.
Blanket wiping with 1 g metsulfuron per litre of water can provide fairly selective control in clover based pastures.
Spinnaker at 100 mL/ha in autumn provides 50-70% control of Dune Onion Weed seedlings, reduces grasses and has little effect on legumes. Higher rates only improve control marginally and cause more damage to pasture grasses.

Thresholds:

Stock carrying capacity has been reduced by up to 75% in areas where onion weed has established.

Eradication strategies:

Eradication will be difficult and take a number of years because of the hard seed bank in the soil.
Manually remove isolated patches before flowering. Tops tend to break off and the plant regrows so ensure that roots are removed when pulling it up.
Cultivate in summer to kill old plants and repeat in the following summer to control seedlings that have established. (Cultivation when the soil is wet is usually ineffective).
Wick or blanket applicators and sponge gloves using 5 g metsulfuron(600g/kg) or 500 mL glyphosate(450g/L) plus 2.5 mL wetting agent per litre of water are useful in sensitive areas or over legume based pastures.
Larger areas can be sprayed with 5g/ha metsulfuron plus 1% spray oil in winter to spring annually until no more seedlings emerge. This will kill most legumes so nitrogen fertiliser will be required to keep the remaining grass productive and competitive. For hand spraying use 0.1 g metsulfuron(600g/L) plus 100 mL spray oil in 10 L water.
2 years after the last metsulfuron spray plant a crop or establish a competitive pasture such as lucerne or medic or replant shrub and tree species. Apply recommended fertiliser levels.
Eradication will take a number of years because of the dormant seed bank in the soil.
Basta® or Spray.Seed® at 2 L/ha are also useful in non-selective situations.
Metsulfuron generally provides better control than chlorsulfuron.

Herbicide resistance:

Biological Control:

Fusarium a root rotting fungus occasionally kills areas of Onion weed, but it generally establishes again in following years.
Another fungus Puccinia barbeyi is being investigated for biocontrol.

Related plants:

None.

Plants of similar appearance:

Onion grass (Romulea rosea) has purple flowers, and a bulb and has solid, smaller leaves and is called Onion Weed in some areas.
Three-cornered Garlic (Allium triquetrum) has bulbs, a triangular stem and a strong odour.
Native Leek (Bulbinopsis semibarbata) is a WA native plant and occurs in similar areas. It has yellow flowers with 6 petals and is up to 15 mm diameter. It is readily eaten by stock.
Dune Onion Weed (Trachyandra divaricata) tends to occur near the coast, has white flowers with distinctive yellow stamens and the leaves are strap like and not hollow.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P31. Photo.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P340. Diagram.

Ciba Geigy (1982) Grass Weeds 3. CIBA GEIGY Ltd, Basle, Switzerland. P120. Diagrams.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P182. Photo.

Hyde-Wyatt, B.H. and Morris, D.I. (1980) The Noxious and Secondary Weeds of Tasmania. (Tasmanian Department of Agriculture, Hobart, Tasmania). P100-101. Diagram.

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). #139.1.

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). p778.

Meadly, G.R.W. (1965). Weeds of Western Australia. (Department of Agriculture - Western Australia). P49-52. Photo. Diagram.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P90-92. Photos.

Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). p16. Photos. Diagram.

Acknowledgments:

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