Lesser Broomrape

Orobanche minor Smith

Family: Orobanchaceae.

Names:

Orobanche is from the Greek orobos meaning vetch and ankhein meaning to strangle referring to its parasitism on vetches and legumes.
Minor is Latin for small because it is the smallest member of the genus.
Lesser Broomrape because it is a small and Broomrape comes from Broom, a leguminous plant, which it often parasitises or rapes.

Other Names:

Clover Broomrape.

Summary:

A brown, erect, single stemmed, root parasite with scale like leaves. It is sticky to touch and has an underground "bulb" and brownish flowers tinged with purple from August to November.

Description:

Cotyledons:

Two.

Leaves:

Leafless but with scale leaves on the stem.
Scale leaves - Alternate, brown, scale like, 13-22 mm long x 3-6 mm wide, narrowly egg shaped to narrowly triangular. Sparsely glandular hairy.

Stems:

Flower stem - Yellow brown often tinged with purple, erect, thick fleshy, swollen at the base, single, unbranched, 100-500 mm tall, sometimes almost translucent, sticky to touch. Hairy with multicellular glandular hairs.

Flower head:

Dense terminal spike with egg shaped, acute tipped bracts that are as long or longer than the petals. Cylindrical with many tubular flowers. Denser near the top.

Flowers:

White, yellow or purple, tubular, bisexual, 2 lipped.
Ovary - Superior, 4 placentas, many ovules. Slender style. 2 lobed, purple stigma.
Sepals - 2, narrowly egg shaped, as long as the petal tube, with 2 slender awl shaped lobes. Usually with tiny bracts attached to the base.
Petals - White to yellow tinged with purple veins to pale purple, tubular and parallel sided, curved outwards and downwards, 10-20 mm long, 2 lipped. Upper lip, 2-3 mm long, equal to or shorter than the lower lip. Upper lip notched with lobes pointing forwards. Lower lip 3 lobed with obtuse tips and finely wavy edges. Middle lobe kidney shaped.
Stamens - 4, in two pairs, 8-10 mm long, attached 2-3 mm from the base of the petal tube. Filaments sparsely hairy and swollen near the base.
Anthers - 1 mm long, 2 celled with tiny points at the base, opening by a longitudinal slit,

Fruit:

Slightly flattened, elliptical capsule, 7-10 mm long x 2.5-3.5 mm wide, releases seed through 2 slits often on the underside. Hairless.

Seeds:

Many, brown to black, tiny and dust like, less than 0.5 mm long, honeycomb pattern on the surface. Up to 500,000 per plant.

Roots:

Thick, fleshy and attached to host plant. Has a tubers or bulb like structure below ground.

Key Characters:

Alternate, brown, scales for 'leaves'.
Stems erect, thick fleshy, unbranched and yellow brown often tinged with purple,
White, yellow or purple, tubular flowers
Corolla tube parallel sided and not swollen.
No chlorophyll or green parts.

Biology:

Life cycle:

Annual. Seeds germinate in autumn and it grows completely underground until it sends up a flowering stem in late winter to spring. Dies with the onset of summer.

Physiology:

Parasitic on the roots of clover, chickpeas, capeweed, skeleton weed and other plants.
It has no chlorophyll, so it is totally dependent on its host for nutrition.

Reproduction:

By seed.

Flowering times:

August to November in Perth.
Winter and spring in WA.

Seed Biology and Germination:

Seed may remain dormant for up to 10 years.

Vegetative Propagules:

None.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Origin and History:

Europe. North Africa. New Zealand (Lazarides).

Distribution:

ACT, NSW, QLD, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Temperate.

Soil:

On a range of soils.

Plant Associations:

Clover and legumes.

Significance:

Beneficial:

Ornamental.

Detrimental:

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

Toxicity:

Not recorded as toxic.

Legislation:

None.

Management and Control:

Pre emergence imazethapyr and chlorsulfuron provide good control.
Pre emergence imazaquin, triasulfuron, primisulfuron, acetochlor and metazachlor provide suppression.
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%.
The following treatments are used overseas to suppress Broomrape and improve the effectiveness of post emergence treatments;
In heavy infestations the seed of Faba beans or peas may be treated by soaking in a mixture of 1 litre of Spinnaker in 20 litres of water for 3-5 minutes before planting.
Lentils are soaked in 1 litre of Arsenal in 20 litres of water for 3-5 minutes before planting.
Sunflowers are soaked in 1 kilogram of Kerb in 20 litres of water for 3-5 minutes before planting.

Eradication strategies:

Remove host.
Spray with imazethapyr(100 mL/ha Spinnaker® post plant, pre emergence) or low rates of glyphosate(100 mL/ha Roundup® CT post emergence) or chlorsulfuron(Glean® 15g/ha post plant, pre emergence) depending on the situation.
In clover, medic or serradella pastures, 100 mL/ha of Spinnaker® just after the opening rains and repeated in mid to late winter if necessary is worth trying on a small trial area. This treatment may also reduce grasses and other weeds such as turnips and radish which may reduce feed available.

Herbicide resistance:

Biological Control:

Related plants:

Australian Broomrape (Orobanche cernua var. australiana) is found in association with Senecio spp.
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.

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P194. Photo.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P332-333, 335. Diagram.

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). P188. Photo.

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #910.3

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. Diagram.

Acknowledgments:

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