PASTORALISTS have been asked to keep an eye out for prickly acacia following the discovery of a large infestation in the east Kimberley.
Department of Agriculture plant pest manager Damian Collopy said it was the second time in a year that the serious weed has been found in the Kimberley.
²WA was thought to be free of prickly acacia until the discovery of one plant in the east Kimberley in 2002 and another plant in a separate part of the east Kimberley in September 2003," Mr Collopy said.
"A Department biosecurity officer carrying out routine surveillance near Durack River found an infestation covering an estimated 100km2 in varying density from scattered plants to very dense stands.
"It is estimated that the plants have been present for more than twenty years."
The infestation is in a remote and inhospitable area, which is seldom visited. Improved road access has allowed vehicles in for the first time in many years.
Mr Collopy said prickly acacia could be identified by its distinct seed pods, which were flat and 10-15cm long. They had narrow constrictions between the seeds, which made the pod look like a straight string of beads.
The pods turn grey when ripe.
Prickly acacia is declared P1 and P2 under the Agriculture and Related Resources Protection Act 1976 and must be eradicated.
"Prickly acacia has the potential to infest many thousands of hectares in WA if allowed to get out of control,² Mr Collopy.
³It is one of the 20 weeds of national significance and is estimated to cover more than seven million hectares, mainly in Queensland, with some infestations in the Northern Territory.
"Prickly acacia is spread when animals ingest and then pass viable seeds.
"Pastoralists are being asked to remain vigilant to the possibility that the weed may be growing in other areas of the state."
The Department of Agriculture will undertake aerial surveillance of the surrounding area to determine the full extent of the infestation.
The department will undertake a risk analysis on the pathways of the weed spreading and the possible use of quarantine restrictions.
Staff will investigate the possible sources of the infestation and any other information that could lead to the discovery of other infestations.