Bathurst Burr
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Xanthium spinosum
Origin. South America.
Distribution in Canberra Region. Disturbed and pasture areas, particularly where sheep grazing has been a major practice.
Dispersal. Burrs cling firmly by hooked spines to animal fur, socks, gloves etc; also dispersed by water.
General Description and Biology
Can grow to 1 m high and 1.5 m wide.
It has a main stem with branches radiating upwards, somewhat like a cypress in overall shape.
Leaves are shiny dark green, but whitish underneath, with prominent yellowish veins.
There are 3 very sharp yellowish spines, 2-3 cm long, at the base of each leaf stalk.
Seeds form within the branches, coming to the surface when mature.
Male flowers are in end-positions; female flowers are in the angle between leaf & stem or branch.
Burrs, each containing 2 seeds, are bean-shaped, to 1 cm long, covered with hairy hooks.
If mature stems are cut and left e.g. on the ground, seeds can actually break out of stems as they dry up.
One large plant can contain 10-20 000 seeds; but few of those seeds actually germinate.
Because of this behaviour and the adhesive character of the seeds, this is one of the most dangerous weeds in open or disturbed areas.
Control Method
a. Manual
The best method is to pull out the entire weed and roots, shortly after a rainfall.
The stems and roots are strong enough to allow them to be pulled out whole.
If simply cut off, the weed usually grows again from the root� though not for some weeks.
By summer, if the weed is pulled and discarded, seeds will hatch from the stems as they dry, and grow.
Therefore the whole plant should be collected in tough (stand-up) bags and sent for incineration.
Large plants need to be cut into portions, branch by branch, to fit conveniently in the bags.
Very large ones � too big for pulling - may need to be dug out with a mattock.
In handling this weed care should be taken to avoid the sharp thorns.
They contain a toxic nerve-irritant substance whose painful effects can last a whole week.