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Northland Regional Council Dargaville-based Biosecurity Officer Peter Joynt says Bathurst bur is a very unpleasant weed that is difficult to control due to the extreme longevity of its seed.

Council staff are aware of sites where Bathurst bur seed has germinated as long as 40 years after the plant was last seen there.

“To successfully control this weed you must destroy the plant at this time of the year, before it can mature and form burs,” Mr Joynt says.

Bathurst bur is an annual plant that grows up to a metre tall. It has branching upright stems with groups of three extremely sharp spines at the base of every leaf. The leaves are three-pronged, narrow and pointed, with a distinctive white midrib.

Bathurst bur seed germinates from November to February and mature plants are usually found in late summer. The bur or seedpod, which develops from mid summer, is readily carried and spread by animals, clothing and machinery.

Mr Joynt says the plant tends to grow in bare land around troughs and gateways and because stock won’t touch it, thickets of it usually spread unchecked. Cultivation of infested land in late spring will germinate a large proportion of the seed in the soil and allow effective control.

Bathurst bur can be effectively controlled by grubbing or spraying prior to flowering and seeding with Escort, 2-4D or Tordon Gold. It is important to follow the manufacturer’s recommendations when spraying.

“However, it is really important to remember that once the bur is formed the seed is viable, even if the plant is sprayed or grubbed out. Any plants with burs must be removed and burned.”

Mr Joynt says Council Biosecurity Officers at Regional Council Offices in Whangarei, Dargaville and Kaitaia can give advice on the control of Bathurst bur and other weeds.