Galvanised burr (Sclerolaena birchii)

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Impact

Galvanised burr is a native plant of the Chenopodiaceae family, which includes other roly-poly plants, saltbushes and crumbweeds. It is regarded as a weed because it is generally not eaten by livestock, it contaminates wool, and it competes with plants that do provide feed. 

Galvanised burr is not usually eaten by stock because of its spiny burrs. Dense infestations occur periodically, causing concern to graziers. The most serious impact caused by galvanised burr is that it reduces wool values by causing vegetable fault.

Spines that become detached from the burrs are problematic for wool-processing as they can become aligned with the wool fibres in spun yarn. Galvanised burr is only one of many species that can cause this type of fault in wool.

The spines and burrs are a considerable nuisance to shearers, stock and working dogs. At times when shearers are in high demand, they may choose to avoid shearing where sheep are carrying large numbers of burrs. Dense infestations also impede stock movement and block cultivation machinery.

Galvanised burr can provide some benefits. Shoot tips and seedlings are a food source in drought, containing 12–18% protein with digestibility of 46%. In western NSW galvanised burr is known colloquially as Hermidale or Girilambone lucerne. It can also be useful as a pioneer plant on bare areas, collecting windblown grass seed, protecting young seedlings from grazing and reducing erosion.

Distribution

Galvanised burr is native to the temperate and semi-arid regions of New South Wales (NSW) and Queensland. Extensive populations of galvanised burr are generally restricted to central and western areas of NSW and Queensland between latitudes 21° S and 36° S across areas receiving between 350 and 650 mm of annual rainfall, although plants have been recorded from as far east as Wingen in the Hunter Valley and Killarney in Queensland.

Small populations of galvanised burr have been recorded in South Australia from areas east and south of Port Pirie, but extensive populations have never developed. Similar populations have been recorded in areas of the Northern Territory around Alice Springs.

The Great Dividing Range forms a barrier to eastern spread as galvanised burr requires mild winter temperatures. Its need for a fairly even seasonal spread of rainfall reduces its southerly spread into dry temperate areas and its northerly movement into the tropics. Slow initial growth rates of seedlings and slow root growth prevent permanent establishment of galvanised burr in arid areas where rainfall events are irregular and unreliable.

Distribution of galvanised burr in NSW
Distribution of galvanised burr in NSW (Auld & Martin 1975).

Spread

Galvanised burr seeds germinate throughout the year but most germination occurs in autumn and spring. Seedlings cannot tolerate moisture stress and establishment depends on rain occurring shortly after germination, and lack of competition from other species. Seedlings flower 8 weeks after germination and produce viable seed by 12 weeks.

Mature galvanised burr plants flower throughout the year. Seed develops within the spined woody burr that is firmly attached to the stem. Each burr contains only one seed but large bushes produce many burrs. Mature seed is sealed within the burrs and receives no sap flow from the mother plant allowing seeds to remain viable after the plant itself dies.

Mature plants are usually short lived. Many plants die within two years and few plants survive for more than four years. When a plant dies its tap root breaks allowing the dead bush to roll in the wind. Seeds are distributed as stem segments and burrs break off. Dead bushes commonly accumulate along fencelines. Stem pieces and burrs can also be spread by animals.

The woody burrs must breakdown enough to allow water to enter so that the seed can germinate. This process takes between 1 and 4 years depending on whether the burrs remain on the surface or are buried.

Over a period of years the density of galvanised burr populations will wax and wane. Numbers of plants fall close to zero during long droughts and rise sharply when seasonal conditions are more favourable to germination and growth. The slow breakdown of the woody burrs during long droughts can create large numbers of viable seeds in the soil (the seedbank).

Adequate rainfall in winter will result in high germination rates of galvanised burr. When this is followed by rainfall in spring or early summer, a dense stand of galvanised burr will result, creating what is known as a “burr year”.

Description

Galvanised burr is a densely branched, hemispherical, short-lived, perennial shrub about 1 m in height and diameter, with stout woolly branches. The common name relates to the dense covering of fine white hairs that gives the plant a blue-green “galvanised” appearance. 

Leaves are flat with a broadly egg-shaped outline, 4-7 mm wide and 12-15 mm long, shortly stalked, and covered with short white hairs.

Flowers are solitary in the leaf axils (where the leaf stalk joins the stem). Flowering occurs most of the year.

Fruiting bodies (burrs) are woolly, 2-3 mm in diameter with 4-5 spines. The spines are almost horizontal, with two shorter spines occurring closer together, and 2-3 longer spines spreading and about 5-15 mm long.

Habitat

Galvanised burr is largely restricted to soils of light surface texture. 

Acknowledgements

Author: Phillip Blackmore

Technical reviewers: Stephen Johnson, Bob McGufficke, Birgitte Verbeek

References

Auld, B.A. and Johnson, S.B. (2011) The biology of Australian Weeds 57. Sclerolaena birchii (F.Muell.) Domin. Plant Protection Quarterly 26 : 1, 2-7.

Auld, B.A., (1973). The effect of herbicides on the germination of galvanised burr (Bassia birchii). Australian Weeds Research Newsletter 18 : 22-3.

Auld, B.A., (1976). The biology of Bassia birchii (F.muell.). Weed Research 16 : 323-30.

Auld, B.A. And Martin, P.M., (1975). Morphology and distribution of Bassia birchii (F.Muell.). Proceedings of the Linnean Society of New South Wales 100 : 167-78.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. And Leigh, J.H., (1981). Galvanised burr and Black roly-poly. Plants of Western New South Wales. P. 249. Soil Conservation Service of NSW and NSW Government Printing Office, Sydney.

Parsons, W. T. And Cuthbertson, E. G., (2001) Galvanised Burr and Five Spined Saltbush Noxious Weeds Of Australia Pp 379-83 CSIRO Publishing, Collingwood, Vic 3066, Australia.

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Control

Galvanised burr can be suppressed by a range of techniques, however a high level of control on grazing land is generally not economically justifiable.The aim of a control program on grazing land should be to minimise the amount of seed entering the seed bank by reducing the numbers of large plants. This approach will reduce the occurrence and severity of future infestations.

Native Vegetation Act 2003

Clearing native species in New South Wales is regulated by the Native Vegetation Act 2003. Cultivation of land for crop establishment is regarded as clearing.

Clearing of galvanised burr and black roly poly may be permitted under the Native Vegetation Act 2003, subject to restrictions and requirements, for example, on land where galvanised burr has not been cleared in any systematic or conscientious manner, some clearing of galvanised burr as invasive native scrub may be permitted, provided the clearing improves or maintains environmental outcomes; or the clearing of any regrowth of galvanised burr may be permitted subject to time restrictions, i.e. after 10 years.

Seek advice regarding the restrictions and requirements associated with clearing galvanised burr and black roly-poly from your Local Land Services.

Herbicide control

Controlling galvanised burr with herbicide is a two-part process due to there being no sap flow between the plant and its mature seeds. The plants are sprayed and the dead bushes must then be heaped and burnt in order to kill the viable seeds that remain within the dead burrs.

Spraying alone, without burning the dead bushes, only hastens the natural process of seed release and causes significant additions to the seedbank.

Two herbicides are registered for the control of galvanised burr. See Herbicide options for details.

Control work using the “herbicide and heaping” technique is uneconomical and impractical for very large infestations such as those that occur in the parts of the state where galvanised burr is most problematic.

No herbicides are registered to control black roly-poly, but plants can be grubbed from the ground and heaped for burning using a tractor-mounted blade. Seedlings will establish after the parent plants are removed and cultivation can then be used to control the populations of seedlings.

Grazing management

Young galvanised burr plants will die when the basal buds are removed. The basal buds are the growth points from where the branches emerge. The basal buds appear at about six weeks after germination. Although the spines appear at the same time they are quite soft, and sheep are able to graze the young plants. Correctly timed heavy grazing of seedlings (down to 3 mm in height) removes the basal buds from the majority of seedlings and kills them.

In semi-arid areas, galvanised burr populations may be managed through a combination of strategic grazing of seedlings with sheep, establishment of competitive pastures including an annual legume and existing native grasses, and removal of mature plants below the crown (stacking and burning the dead bushes).

Cultivation

Seedlings are unlikely to establish from seed buried to a depth of 40 mm or more. Ploughing arable areas with an implement that inverts the soil will reduce the size of the viable seed bank in heavily infested areas.

Galvanised burr growing on arable country can be managed by a program of appropriate herbicide application, cultivation and cropping.

Biocontrol

As part of a complex native ecosystem galvanised burr is attacked by several insects and diseases, however these organisms cannot suppress large numbers of plants.

Herbicide options

WARNING - ALWAYS READ THE LABEL
Users of agricultural or veterinary chemical products must always read the label and any permit, before using the product, and strictly comply with the directions on the label and the conditions of any permit. Users are not absolved from compliance with the directions on the label or the conditions of the permit by reason of any statement made or not made in this information. To view permits or product labels go to the Australian Pesticides and Veterinary Medicines Authority website www.apvma.gov.au

See Using herbicides for more information.


2,4-D amine 625 g/L (Amicide® 625)
Rate: 320 mL per 100 L of water
Comments: Apply to young, actively growing plants.
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Dicamba 500 g/L (Kamba® 500)
Rate: 600 mL per 100 L of water
Comments: High volume spot spray.
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Dicamba 500 g/L (Kamba® 500)
Rate: 8.8 L/ha
Comments: Boom spray. Use a minimum of 1500 L water /ha. Add a surfactant.
Withholding period: 7 days.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Dichlorprop 600 g/L (Lantana 600®)
Rate: 1.0 L per 100 L of water
Comments: Apply to young, actively growing plants.
Withholding period: Nil.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


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Legal requirements

The content provided here is for information purposes only and is taken from the Noxious Weeds (Weed Control) Order 2014 published in the NSW Government Gazette, detailing weeds declared noxious in New South Wales, Australia, under the Noxious Weeds Act 1993. The Order lists the weed names, the control class and the control requirements for each species declared in a Local Control Authority area.

Area Class Legal requirements
Bland 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management
Federation 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management only in the area formerly known as Urana Shire Council
Forbes 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management
Lachlan 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management
Leeton 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management
Lockhart 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management
Mid-Western Regional 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management
Moree Plains 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management
Murray River (formerly Wakool) 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management only in the area formerly known as Wakool Shire Council
Murrumbidgee 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management only in the area formerly known as Jerilderie Shire Council
Narrabri 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management
Narromine 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management
Parkes 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management
Wagga Wagga 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management
Wentworth 4 Locally Controlled Weed
The plant must be controlled where it impacts on normal agricultural practices including cropping and pasture management

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For technical advice and assistance with identification please contact your local council weeds officer.
For further information call the NSW Invasive Plants and Animals Enquiry Line on 1800 680 244 or send an email to weeds@dpi.nsw.gov.au

Disclaimers

Pasture improvement may be associated with an increase in the incidence of certain livestock health disorders. Livestock and production losses from some disorders are possible. Management may need to be modified to minimise risk. Consult your veterinarian or adviser when planning pasture improvement. The Native Vegetation Act 2003 restricts some pasture improvement practices where existing pasture contains native species. Inquire through the NSW Office of Environment and Heritage for further details.

Reviewed 2016