Family: Asteraceae (daisies)

Status: Bathurst, Californian and Noogoora burrs are noxious in category W2 (must be continually suppressed and destroyed) in Eurobodalla and Shoalhaven Local Governments Areas, and in category W3 in Bega Valley Shire (must be prevented from spreading and infestation reduced to the satisfaction of Council).

Description:
An erect annual herb, usually about 1m high, which may be single stemmed if small but usually branched. Stems are finely hairy, and carry a 3-pronged spine at the base of each leaf. Leaves are dark green and shiny above, and whitish with downy hairs below, with small lobes on the leaf margins. Flowers are inconspicuous. Two seeds are contained in a spiny burr, about 10mm long.

Preferred habitat and impacts:
Generally found growing in full sun on grazing land, roadsides or waste ground, preferring moist soil. Prefers disturbed sites with fertile soils such as stock camps or riverbanks. Burrs are an important cause of vegetable contamination of wool in wool growing areas, making fleeces harder to work with and reducing their value. Seedlings are poisonous to livestock, particularly horses and pigs. Some people may develop dermatitis after contact with the plant.

Bathurst and related burrs may be a weed of remnant native grassy vegetation in farming areas, although given their preference for sites with enhanced fertility, this is not very likely. Most such sites carry a higher proportion of weeds than of natives.

Dispersal:
Burrs attach to livestock, clothing, and are spread in mud and soil. They float on water.

Look-alikes
Californian burr (Xanthium orientale ) and Noogoora burr (Xanthium occidentale ) have similar but larger burrs (to 25mm), and lack the 3-pronged spines. Their leaves are large, lobed and toothed like a grape leaf.

Another weed, common thornapple (Datura stramonium ) has grape-like lobed leaves and a spiny seed capsule, but its capsule is larger than that of the xanthium burrs, and contains numerous seeds, not two as in Xanthium. It also has very showy white trumpet flowers.

Control
Small infestations can be chipped out prior to the burrs forming or spot sprayed. Once burrs have formed, seed may mature even after plants have been cut. If this occurs the cut plants will need to be burnt. Selective herbicides can be used to remove them from pasture.