Environment

Bathurst bur

Bathurst burBathurst Bur

Common names:
Bathurst bur, spiny cocklebur

 

Scientific name:
Xanthium spinosum

 

Regional classification:
Total control

 

National classification:
National Pest Plant Accord – banned from being sold, propagated or distributed

Description

Bathurst bur is a pest plant in Northland and cannot be legally propagated, sold or distributed.

 

Bathurst bur is of limited distribution in Northland, found mainly in the cropping areas of Kaipara district. It is mostly a weed of kumara and other crops, but also infests roadsides, pasture and other land.

 

Bathurst bur is an erect, well branched, annual herb up to one metre tall which grows from a branched taproot.

 

Stems:

  • yellow-green stems
  • armed at the base of each leaf stalk and stem joint
  • has one or two three-pronged yellow spines
  • each prong about 2cm long

Leaves:

  • up to 7cm long, narrow and pointed
  • mostly three-lobed with the middle lobe longer than the others
  • leaf upper surface is a shiny dark green with a prominent white midrib
  • underside is pale green and downy.

Flowers:

  • tiny and greenish-cream in colour
  • seed capsule oval straw coloured bur, 15mm by 5mm, covered in numerous slender yellow hooked spines
  • inside each bur are two brown or black flattened seeds, each about 1cm long
  • seeds germinate from November to January

Why is it a problem?

Burs remain attached to dead plants until they are trampled or transported elsewhere by animals. One of each pair of seeds germinates the following summer and the other remains dormant for two to three years, occasionally up to 15 years.

 

The burs cling fast to wool, fur, sacking, clothing and any fibrous material. Seeds are therefore mainly dispersed by animals and people.

 

Uncertified seed in summer crop species such as maize, sorghum and sunflowers can also be contaminated by burs. Bird seed, poultry feed, horse oats and produce such as tomatoes can also carry burs.

 

Bathurst bur is a serious weed of sheep farms as the burs contaminate wool, adding considerable costs to the grower. They also irritate the skin of shearers and cause shearing combs to jam and break.

 

The plant’s spines damage the feet and skin of all livestock. The plant is mildly poisonous, and can cause contact dermatitis in some people.

What can I do?

  • The best long term control option includes pasture renewal, ideally with a summer of fodder cropping. This will germinate a large proportion of the dormant seed and allow easy control.
  • Grub, pull or spray plants before they set burs. Collect and burn plants with mature burs.
  • The majority of seed germinates from November onwards, in areas where the soil is bared or disturbed. Mature plants are usually found from mid-summer to autumn.
  • Seed will not germinate through a dense grass sward and can remain dormant for many years.
  • Isolated plants may be pulled by hand or grubbed out. 
  • Spot spray with herbicide prior to plants setting burs.
  • Total spraying out and cultivation of infestation sites in late spring will encourage a high percentage of the dormant seed in the ground to germinate and allow a high level control to be quickly achieved.

Your responsibility

Bathurst bur is a 'total control' pest plant.  This means that the occupier or owner of a property where the plant is growing must aim at completely eradicating the plant.  It is illegal to sell, propagate, or distribute any parts of this pest plant in the Northland region.

Recommended control methods

Site management:

  • Avoid soil disturbance and bare ground.
  • Maintain good pasture cover to prevent re-establishment.
  • Replant with native species where appropriate.

Recommended approaches:

  1. Grub out plants before flowering (March to April).
  2. Spray before plants set seed (1g metsulfuron + 20ml penetrant/10L or 120ml Tordon Max/10L or 25ml clopyralid/10L or 100ml glyphosate/10L).
    Do not use clopyralid in home gardens.

Caution: When using any herbicide PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.

More information

For further information or control advice please contact one of our Biosecurity Officers at the Northland Regional Council on 0800 002 004:

  • Whāngārei: Sara Brill
  • Dargaville: Carl Cooper
  • Kaitāia: Doug Foster