Pest plant - Bathurst Burr

Bathurst burr (Xanthium spinosum) is a spiny annual weed. Successful control requires treatment of seedlings and the following germinations. It is important to keep Bathurst burr off clean properties or to recognise and destroy new infestations before they become established.

Description

• erect, densely branched annual herb to 1m high
• leaves are dark green and shiny on upper side, underside is pale green and downy
• leaves are 7cm long and usually have 3 lobes, at the base are 3-pronged yellow spines, 1.5-2.5cm long
• flowers are small, creamy-green, at the end of stems and also at leaf nodes
• the burr is straw coloured and oblong in shape, 1-1.5cm long and 4-5mm wide, covered with hooked spines
• each burr contains two seeds that are flat, black and 1cm long
• plant has a branched taproot.

Why is it a problem?

• burrs of this plant contaminate wool, adding to the cost of handling and processing, as well as to the final cost of the woollen product
• spines of this plant cause physical damage to stock, people and shearing machinery
• competes strongly with summer crops and is host for horticultural diseases
• seedlings are poisonous to most stock animals (the toxin is hydroquinone).

Distribution

• Eyre Peninsula – isolated plants, especially after rain
• Northern pastoral – very common but decreasing further north
• Northern agricultural districts and Yorke Peninsula – widespread
• Murray Mallee – scattered infestations
• South East - scattered with some large infestations
• Central region – scattered

Ecology

• prefers highly fertile disturbed soil, often found near watercourses, dams and flood plains
• staggered germinations occur after late spring and summer rains, or irrigation
• grows quickly in warm weather, burrs are formed in February and continue for several months
• newly germinated plants can produce burrs at a few weeks of age
• most plants die in early winter
• seeds can germinate out of season and mature plants can be found at any time of year.

How it spreads

• by animal movement, the hooked spines on the burrs cling to wool and fur
• burrs are also easily carried on clothing, packaging and water, and may contaminate summer crops.