Bathurst bur

Scientific name: Xanthium spinosum

Bathurst bur

Bathurst bur

Bathurst bur leaves

Bathurst bur

Bathurst bur

Bathurst bur

Bathurst bur

Bathurst bur in maize crop

Bathurst bur seedling
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • An erect, branched annual herb, growing up to 1 m high (but usually shorter, about 30–60 cm in height). It is often ‘shrubby’ in appearance
  • Most plants grow over summer but a few mature plants can be found in all seasons
  • Leaves are dark green on the upper surface and paler green on the back, up to 7 cm long and usually with three unequal lobes
  • Composite flower heads comprise many small, creamy green flowers arranged in a tight clump. These develop into characteristic green to straw-coloured burs, each1.0–1.5 cm long, with many yellow hooked spines. Each bur contains two seeds.
  • Stems are branched
  • One or two three-pronged, vicious yellow spines, each about 2 cm long, at the base of each leaf stalk
  • Small, creamy green flowers develop into characteristic straw-coloured burs, each1.0–1.5 cm long, with many yellow hooked spines. Each bur contains two seeds.

Origin

  • Originated in South America and accidentally introduced into Australia in the early 1800s (near Bathurst, as well as other places) from contaminated grain or livestock imports. It is now one of the most widespread weeds in Australia and is common in many parts of the world
  • Bathurst bur found its way to New Zealand by the 1860s and in the 1890s was reported as spreading in many areas – notably around Gisborne, Auckland Province and Bay of Plenty
  • Most commonly found today in eastern areas of the North Island and in a few places in the South Island
  • Classified as ‘noxious’ in 1900 and now considered a ‘pest plant’ by many regional councils
  • Grows in pasture, on arable land, in coastal areas and in waste places, especially where the ground is bare of vegetation for part of the year.

Life cycle

  • Usually germinates during late spring and early summer, produces burs in February and dies in early winter
  • Although mostly a summer-growing plant some seeds can germinate out of season so mature plants can sometimes be found at any time of the year
  • Of the two seeds present in each bur, generally only one will germinate in a single season. The other seed will remain dormant for a year or two
  • Burs are usually spread by becoming attached to wool or socks! They can also float and are spread along watercourses
  • Plants are mildly poisonous to livestock, and can cause contact dermatitis in some people
  • Tends to occur in high fertility, moderately warm situations and is particularly common around stockyards, stock camps and tracks, gateways and races
  • Bathurst bur may become more widespread and problematical as climate change could result in higher temperatures and less rain in some areas.

Benefits

  • Young plants are mildly poisonous to stock, older plants have vicious spines, and produce burs that contaminate wool and socks, and can cause dermatitis in some people. Benefits? Absolutely none!

Impact on farming

  • Bathurst bur is mainly a pasture weed but it is also a weed of summer growing crops
  • Contamination of pastures and stock can reduce agricultural productivity
  • A single bur in a pack of wool can lead to rejection or down grading the entire consignment.

Impact on pasture

  • Burs are easily spread from one place to another and once populations are established plants will repeatedly re-appear from buried seeds
  • Plants can out-compete and replace desirable grasses and clovers, and the spines discourage stock from grazing close to desirable plants plants leading to poor pasture utilisation.

Impact on stock

  • Burs become entangled in wool, leading to its downgrading as they are difficult to remove
  • Burs also damage the feet of sheep and other stock when they walk through dense patches.

Prevention and early eradication

  • Be careful not to import hay from farms where the weed is prevalent, and ensure contractors don’t bring it onto your farm from contaminated properties
  • Uncertified seed in summer crops such as maize, sorghum and sunflowers can also contain burs.
  • Removing the first few plants that appear on the farm can pay big dividends by saving on future costs. Pulling plants out (carefully – watch those spines!) and putting them in plastic bags before burning or burying them very deeply is probably the best treatment for those first few. Take care not to spread the seed around
  • After using herbicides, competitive pastures must be maintained to reduce re-infestation.

Grazing

  • Grazing is not an effective method of control.

Mowing

  • Mowing is not usually an effective control method. Rotary slashing can be used but must be done before any burs are formed, and plants may still regrow afterwards.

Pasture species/cultivars

  • The best long term control option is probably pasture renewal, with a summer of fodder cropping. A large proportion of the dormant seed will then germinate and allow easier control
  • Establishment of more competitive and locally-appropriate pasture species may reduce the incidence of Bathurst bur by shading it out
  • A dense sward of sown pasture species, especially in late spring but preferably all year round, prevents plants from establishing.

Chemical control

  • Control programmes should aim to prevent seeding for 3 or 4 years
  • In pasture young plants can be controlled with broadcast applications of 2,4-D or MCPA, preferably before any burs are produced
  • Metribuzin, picloram, dicamba, 2,4-DB, MCPB, atrazine and pendimethalin have all been used selectively in the appropriate crops, refer to specific product labels and cropping guides for their use
  • Mature plants in pasture will require spot treatment with herbicides which will damage either the grass or the clover (or in some cases both) component of the pasture sward, refer to table below for options
  • One recommendation is to spray before plants set seed with metsulfuron + penetrant, clopyralid or glyphosate
  • All of these will damage clovers: clopyralid does NOT damage grasses and will not result in bare ground but both have residual activity. Metsulfuron kills some species of grasses, but not all, and it again has residual activity
  • Glyphosate kills any green plants and results in bare ground in which new seedlings of Bathurst bur can emerge, but it has no residual activity
  • Clopyralid can contaminate lawn clippings and and these must NOT be composted.

It is recommended that with the exception of 2,4-D all the chemicals below only be used as spot treatments in pasture. They may be used over larger waste areas.

Active ingredient When to apply Residual effect Grass Damage Clover Damage
glyphosate spring/summer none severe severe
metsulfuron spring/summer short moderate severe
picloram (prills) spring/summer moderate slight moderate
picloram (gel) apply to freshly cut stump anytime short none severe
triclopyr spring/summer short none (except kikuyu) severe
triclopyr/aminopyralid spring/summer long none (except kikuyu) extremely severe
picloram/triclopyr spring/summer moderate slight severe
picloram/metsulfuron spring/summer moderate moderate severe
2,4-D spring/summer short none slight
clopyralid spring/summer short none severe

Biocontrol

  • No biological control agents are available for Bathurst bur
  • A fungus (Colletotrichum orbiculare) that causes anthracnose and seedling blight in Bathurst bur was observed in New South Wales in 1948 and was tested as a control agent, but did not prove reliable enough to be of practical use
  • Other insects and fungi attack Bathurst bur but outbreaks are spasmodic and none have given long-term control.

  • Hocking PJ, Liddle MJ 1995. Xanthium occidentale Bertol. complex and X. spinosum L. In: Groves RH, Shepherd RCH and Richardson RG eds. The Biology of Australian Weeds, Volume 1. RG and FJ Richardson Publishers, Melbourne, Australia. Pp. 241-289
  • Northland Regional Council, 2014. Bathurst bur (Accessed 25 August 2014)
  • Parsons WT, Cuthbertson EG 1992. Bathurst burr: Xanthium spinosum L. In: Noxious Weeds of Australia. Inkata Press, Melbourne and Sydney, Australia. Pp 318-321
  • Popay I, Champion P, James T 2010. An illustrated guide to some common weeds of New Zealand. NZ Plant Protection Society, Christchurch, New Zealand. 416 p.