Australian Broomrape

Orobanche cernua Loefl. var. australiana (F.Muell and Tate) J.M.Black ex G.Beck

Synonyms - Orobanche australiana

Family: Orobanchaceae.

Names:

Orobanche is from the Greek orobos meaning vetch and ankhein meaning to strangle referring to its parasitism on vetches and legumes.
Cernua
Australian Broomrape comes from Broom, a leguminous plant, which it often parasitises or rapes.

Summary:

A brown, erect single stemmed, perennial, root parasite with scale like leaves.

Description:

Cotyledons:

Two.

Leaves:

Alternate. Brown and scale like, 10-15 mm long, egg to lance shaped, acute tip.

Stems:

Flower stem - Brown and sometimes tinged with blue, erect, stout, unbranched, 200-400 mm tall. Many glandular hairs.

Flower head:

Terminal, dense spike with each flower in the axil of a bract that is shorter than the flower. Cylindrical with many tubular flowers.

Flowers:

White to pale blue or purple, tubular, bisexual, 2 lipped.
Ovary - Superior, 1 celled, 2-4 placentas, many ovules. Slender style. Stigma white to yellow, 2 lobed, bent down.
Sepals - 2, egg shaped, 8-10 mm long, acute tipped, smooth edged or toothed on one side, usually 5 nerves. More than half as long as the corolla tube. Sometimes with a tiny third sepal.
Petals - 18-20 mm long, purple, tubular, curved, swollen below the middle of the tube where the anthers are inserted and contracted above the middle, limb bent down, 2 lipped. Upper lip 2 lobed. Lower lip with 3 rounded, spreading lobes.
Stamens - 4, in two pairs, attached inside the petal tube.
Anthers - 2 celled with tiny points at the base, opening by a longitudinal slit,

Fruit:

Capsule with withered petal tube, egg shaped to oblong releases seed through slits, 2 valves.

Seeds:

Many, brown, tiny and dust like. Embryo straight with a very short radicle. Up to 500,000 per plant.

Roots:

Thick, fleshy and attached to the host plant.

Key Characters:

Alternate, brown and scale like leaves.
Erect, brown, unbranched stems sometimes tinged with blue.
Corolla tube swollen below the middle where the anthers are inserted.
Adapted from John Moore.

Biology:

Life cycle:

Perennial. Seeds germinate in autumn and it grows completely underground until it sends up a flowering stem in spring.

Physiology:

Parasitises the roots of other plants.
It has no chlorophyll, so it is totally dependent on its host for nutrition.

Reproduction:

By seed.

Flowering times:

Spring to early summer in western NSW.
September to December in SA.

Seed Biology and Germination:

Seed may remain dormant for up to 10 years.

Vegetative Propagules:

None.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Spread by seed.
Tends to grow in localised colonies.

Origin and History:

New Zealand.

Distribution:

NSW, SA, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Temperate.

Soil:

Most abundant on sandy soil and especially along drainage lines.

Plant Associations:

Clover, legumes and Senecio spp.

Significance:

Beneficial:

Ornamental.

Detrimental:

Weed of clover and legume pastures and crops, sunflowers, gardens and Senecio species.
Rarely eaten by stock.
The seed is prohibited in produce exported to many countries.

Toxicity:

Not recorded as toxic.

Legislation:

None.

Management and Control:

Pre emergence imazethapyr and chlorsulfuron provide good control (Garcia-Torres et al, 1994).
Pre emergence imazaquin, triasulfuron, primisulfuron, acetochlor and metazachlor provides suppression (Garcia-Torres et al, 1994).
Post emergence glyphosate at low rates around 100 mL/ha of Roundup® CT is useful in some crops and pastures.

Thresholds:

10-20 Broomrape heads per m2 is expected to reduce dry weight of the crop or pasture by about 20%.

Eradication strategies:

Remove host.
Spray with low rates of glyphosate(100 mL/ha Roundup® CT post emergence), imazethapyr(100 mL/ha Spinnaker post plant, pre emergence) or chlorsulfuron(Glean 15g/ha post plant, pre emergence).
In clover, medic or serradella pastures, 100 mL/ha of Spinnaker just after the opening rains is worth trying on a small trial area.

Herbicide resistance:

Biological Control:

Related plants:

Branched Broomrape (Orobanche ramosa) has pale blue flowers and is found on Brassica and legume crops, broad leaved weeds and some native plants.
Lesser Broomrape (Orobanche minor) is found in association with legumes and other broadleaf species.
Crenate Broomrape (Orobanche crenata) has yellow flowers and found in association with legume and vegetable crops and has not been found in Australia.
Egyptian Broomrape (Orobanche aegyptiaca) has blue to purple flowers and is found on Canola, Brassica or Cole crops and other vegetables and has not been found in Australia.
Nodding Broomrape (Orobanche cernua var. cernua) is found on carrots, Lathyrus and vegetables and has not been found in Australia.
Orobanche papaveris is found in association with poppies.

Plants of similar appearance:

References:

Anon (2000). Farmer Alert (2000). Keep your markets safe. Department of Agriculture Fisheries and Forestry.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P775. Diagram.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P604. Photo.

Garcia-Torres, L., Lopez-Granados, F. and Castenjon-Munoz, M. (1994). Pre emergence herbicides for the control of broomrape (Orobanche cernua Loefl.) in sunflower (Helianthus annuus L.). Weed Research, 34:395-402.

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #910.2.

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). P594.

Acknowledgments:

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