Quick Facts

Quick facts

• In Australia, there are currently two introduced species and one relatively rare native species of orobanche.
• Branched Broomrape (Orobanche ramosa) is a parasitic plant whose hosts include many crop plants.
• Because of its microscopic seed it is often found as a seed contaminant in those crops where it grows.
• Contamination with broomrape seed means rejection of crops by importing countries.
• An understanding of its biology and hence the best form of control is still to be achieved.

What Does It Look Like?

What is it?

Broomrapes (Orobanche spp.) are small, erect, branched or unbranched, parasitic herbs, completely lacking in chlorophyll and dependent on other plants for their food supply; they gain their food by attaching to the root system of the host plant. There are three species in Australia, two introduced, Branched Broomrape Orobanche ramosa and Common Broomrape O. minor, and one native species (O. cernua var. australiana) which is not considered weedy and is becoming increasingly rare. Under Victorian legislation, only O. ramosa is listed.

Because of the lack of chlorophyll they generally have a brownish appearance. Gland-tipped hairs may be present on both the stems and in the inflorescence. They have small scale-like leaves arranged alternately along the stems and similar bracts below the flowers. Bisexual flowers are formed towards the apex of the stem, sometimes occupying much of the stem length. The calyx may be joined into a tube at the base and have five equal parts (Branched Broomrape) or it may have four or five unequal parts which do not form a tube at the base (common broomrape and O. cernua var. australiana). The flower is tubular at the base, in Branched Broomrape widening into a throat, but in common broomrape and O. cernua var. australiana, narrowing into the throat. The flower is 2-lipped, more noticeably so in Branched Broomrape than in the other two species. Flower colour is pale blue in Branched Broomrape and common broomrape, but the latter species has darker venation, while flowers are dark blue-purplish in O. cernua var. australiana. The fruit is a capsule containing large number of microscopic seeds (Barker 1999; Faithfull & McLaren 2004).

Because of their parasitic nature many Orobanche species are not desirable. Branched Broomrape is particularly unwanted because of its ability to form attachments to the roots of a very large number of economic plants and significantly reduce yields. The presence of seed in harvested crops may be sufficient to have the crop rejected by an importing country. It is currently only known from South Australia (W.R.Barker 2007, pers. comm.). Common Broomrape is considered to be much less of a problem because it only attaches to plants of much less economic significance. Its spread around Australia has been insidious and it is now widespread in the southern states (AVH 2007).

For further information and assistance with identification of broomrape contact the herbarium in your state or territory.

Flower colour

Blue, White, Purple

Growth form (weed type/habit)

Herb

Where it currently grows? Preferred habitat

There does not appear to be any particular preference for habitat for any of the broomrape species. Branched Broomrape occurs in alkaline sandy soils in the Murray mallee region, while common broomrape and the native species are frequently found in sand hills which might suggest that sandy soils are the best for growth of the haustorium which forms the attachment between the broomrape and the host species. However, one specimen of the native broomrape has been recorded from heavy black clay in Victoria (Barker 1999: W.R.Barker 2007, pers. comm.).

Distribution will presumably be governed by the presence of suitable hosts. Since the number of potential host plants for Branched Broomrape is large, it is a threat to any area where such plants occur. Host plants documented elsewhere include Celery, Chickpea, Tomato, Lettuce, Coriander, Onions, Potato, Sunflower, Tobacco, Canola, White Mustard, Cabbage, Vetch, Carrot, Faba Bean, Cannabis and Clover, as well as a number of weeds and even some native daisies (Faithfull & McLaren 2004; Department of Water, Land and Biodiversity Conservation. updated 2007).

Common Broomrape is a weed of crops and gardens in temperate regions and is occasionally also found in subtropical environments (Navie 2004).

Are there similar species?

Distinguishing between the species of Broomrape in Australia is crucial since one of the species is native and becoming increasingly rare. Since the native species is known only to attach to native plants, particularly native Senecio species, the identity of the host can be a good guide to the species involved (W.R.Barker 2007, pers. comm.).

Common Broomrape (Orobanche minor) is frequently associated with Gazania species, but is also known to attach to legume species such as clovers (hence one of its common names), to Capeweed, and to nasturtiums and petunias (W.R..Barker 2007, pers. comm.).

Branched Broomrape (Orobanche ramosa) attaches to, or has the ability to attach to, a wide range of plants, including crop plants such as Tomato, Lettuce, Coriander, Canola, White Mustard, Cabbage, Vetch, Carrot, Chick Pea, Faba Bean and Annual White Clover (Department of Water, Land and Biodiversity Conservation updated 2007), to other weeds such as Nightshades (Solanum nigrum spp.), Amaranthus species, Brassica spp. and Daisy species such as capeweed (Arctotheca) and Dandelion (Taraxacum). However Branched Broomrape has also been recorded attaching to some native daisies such as Brachyscome and Senecio and so some further distinguishing characteristics are necessary to separate it from the native Orobanche species (W.R.Barker 2007, pers. comm.).

As its name implies, Branched Broomrape has branched stems while the other two species are unbranched. Furthermore the calyx in Branched Broomrape is 5-lobed and surrounds the base of the corolla (floral) tube while in the other two species the calyx lobes do not completely surround the corolla tube but leave the upper part of the tube exposed. The corolla tube of the flowers of Branched Broomrape is narrowed within the calyx, opening into a wider throat, whereas the corolla tube in the other two species is broadest at the base and narrowing into the throat. The petals are more noticeable in the Branched Broomrape flowers and pale blue in the introduced populations in South Australia. Common Broomrape also has pale blue or whitish flowers but has darker venation while the native broomrape has dark blue-purple flower lobes. See Faithfull & McLaren (2004).

Broomrape may also be confused with the Potato Orchids (Gastrodia spp.) with their similar brownish colour but the flowers are very different from the blue-purple flowers of Broomrape (R.M.Barker 2007, pers. comm.).

Why Is It A Weed?

What are its impacts?

Broomrape was included in the list of 71 species that were nominated by state and territory governments for assessment as Weeds of National Significance (WONS). Following an assessment process, Broomrape Bush was not included as one of the 20 WONS. However, it remains a weed of potential national signficance.

Agriculture: Branched Broomrape is such a devastating parasitic weed that it has been known to reduce crop yields by up to 90%. It parasitises a wide range of crops, including vegetables such as Carrots, Tomatoe, Potatoe and beans and also legume crops. A farming area of South Australia has been quarantined for at least 12 years in an attempt to prevent its spread in Australia (cost for one year of quarantine alone is $4.5 million) (Warren 2006). The seed are so microscopic that it is easily spread by a variety of means and also easily contaminates seeds of harvested crops (Holding 2004; W.R.Barker 2007, pers. comm.).

Common Broomrape is a less aggressive species, which attaches to such plants as Gazania and Clover (W.R..Barker 2007, pers. comm.).

How does it spread?

Broomrape seed is microscopic and easily carried by wind, by water or by animals or machinery. Estimates of half a million seeds produced per plant have been cited (Lloyd et al. 2007). Possible vectors cited for distribution of the seed include farm machinery, livestock, soil and harvested crops or fodder (Secomb 2006).

What is its history in Australia?

It is not known how the introduced species of broomrape first arrived in Australia.

The timing of the introduction of Branched Broomrape into South Australia is disputable. There is a single 1911 collection of the species from near Glenelg in the State Herbarium of South Australia. There had been no further suggestions of its presence until a collection from the Murray mallee area was brought into the State Herbarium of South Australia for identification in 1992 (Holding 2004; W.R.Barker 2007, pers. comm.).

Common Broomrape has been in Australia for a much longer period of time since there are collections from the mid to late 1800s (W.R.Barker 2007, pers. comm.).

How To Manage It?

Best practice management

Broomrapes are species targeted for national eradication under the National Resource Management Ministerial Council's National Cost-Sharing Eradication Programmes. These programmes map and monitor the full distribution of the species, and coordinate or undertake activities to eradicate that species from Australia.

Effective control has meant that there has to be an understanding of the biology of Branched Broomrape. Such a programme has been underway since 2002 (Matthews et al. 2006). There is still some confusion surrounding the name which should be applied to the introduced South Australian material (W.R.Barker 2007, pers. comm.).

Non-chemical control: In order to control the outbreak of Branched Broomrape in South Australia the region affected has been placed under quarantine to prevent spread of the weed outside the infected area by livestock and machinery. Legislation and protocols pertaining to the quarantine area is documented in the Code of the Minister for Environment & Conservation (2003). Grain harvesters and other farm machinery must be decontaminated, crops must be inspected before harvest, and movement of grain, straw and livestock is controlled to try to contain the infestation.

Various means aimed at reducing the seedbank of Broomrape within the soil have been tested. These have included fumigation with methyl bromide and Basamid and studies of Interceptor, a product derived from Pinus pulp (Williams et al. 2006). The other method being trialled is "suicide germination" where Broomrape seeds are stimulated to germinate by artificial means rather than by the presence of a trigger from a host (Department of Water, Land and Biodiversity Conservation SA 2007; Virtue et al. 2006). Other techniques for reducing the soil seedbank such as solarisation, trap crops etc. are documented in Virtue & Jupp (2002).          

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

It is thought that specific substances are required to be secreted by the host root before broomrape seeds will germinate. Further triggers are then needed to begin the formation of the haustorium by the broomrape seed. The haustorium is the attachment between the broomrape plant and its host and is the means by which the broomrape plant obtains its moisture and food. Disruption of triggers at this stage of development are some of the ways in which it has been attempted to control the growth of broomrape species (Cooke 2002).

In the presence of appropriate triggers, moisture for a week and a soil temperature between 18 and 23°C, Broomrape seeds are able to germinate and parasitise the roots of the host for up to 50 days. Stems appear in September/October with flowering and fruiting occurring very shortly after. Dried-out plants may persist for some time. Above-ground plants usually only represent a small part of any infestation (Faithfull & McLaren 2004).

Where Is It Found?

Which states and territories is it found?

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

What areas within states and territories is it found?

Apart from an early record from the Glenelg sandhills, Branched Broomrape is presently confined to a small quarantined area in the Murray mallee region of South Australia (Faithfull & McLaren 2004; Holding 2004).

Common Broomrape has a much wider distribution and is found in all states except Northern Territory. It is particularly common in south-west Western Australia and in south-eastern Australia in crop-growing areas from south-east Queensland to the Mt Lofty Ranges in South Australia. It has been in Australia for a much longer period of time since with collections from the mid to late 1800s (W.R.Barker 2007, pers. comm.).

The Native Broomrape species is found in coastal Western Australia and along the Murray River in Victoria, but its main distribution is in inland South Australia towards Lake Eyre and in north-western New South Wales (AVH 2007).

Where does it originate?

Broomrapes are mostly native to Europe and Asia and there are about 140 species worldwide. Some species are more undesirable than others, but Branched Broomrape, Egyptian Broomrape (O. aegyptica), Nodding Broomrape (O. cernua var. cernua), Crenate Broomrape (O. crenata) and Sunflower Broomrape Orobanche cernua var. cumana [as O. cumana] appear to be the worst of them (Faithfull & McLaren 2004). Branched Broomrape is banned in many countries of the world (Scher undated).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, NT, SA, TAS, VIC, WA

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Orobanche spp.

Other scientific names (synonyms)?

Does it have other known common name(s)?

Branched Broomrape, Hemp Broomrape, Clover Broomrape, Common Broomrape