Thursday, 23 May 2013

Emerging weeds in the Top End

Yellow Oleander (NT Dept. Land Resource Management)
The field day at Mt Bundy raised a few interesting and emerging weed concerns. Fergal O’Gara has noticed that Yellow Oleander is suddenly appearing in paddocks. This tree which grows to 10m is a declared weed in Qld and all parts are poisonous to stock and humans if ingested. Fergal also highlighted concern with Neem, a bird dispersed tree with leaves unpalatable to stock.

Scott Witham said Lantana, a Weed of National Significance, appeared more vigorous on his property this year. Lantana is toxic and allelopathic, meaning it releases chemicals into the soil which prevent germination from some other plants. It can alter fire regimes and impact grazing though stock toxicity and loss of productivity.

Lantana (P. Clifton)
Lantana seed is dispersed by birds so perches such as fencelines and trees is often where lantana is first encountered. Lantana is particularly suited to Top End conditions.

Top: Current localised Lantana distribution. Bottom: Potential distribution (From

When invasive species are introduced to a new area they tend to undergo an ‘establishment phase’, a ‘lag phase’ and then an ‘explosion phase’. The lag phase may last for decades before distribution suddenly starts growing exponentially. This was the case with Mimosa pigra and perhaps Lantana and Yellow Oleander are following similar patterns.

Tom Price from Weeds Branch highlighted the presence of two other Weeds of National Significance that are more prominent to the south but getting a foothold in the Top End.

Bellyache bush is one of the most aggressive and poisonous weeds in the dry tropics of northern Australia. Common in the Daly Catchment southwest of Katherine, it forms dense thickets, particularly along watercourses and also invades floodplains, open woodland and grassland. Productive river frontages are often most at risk of invasion. It can reduce biodiversity, restrict access for mustering, and if ingested can potentially lead to death in humans and animals.

 Bellyache Bush (NT Dept. LRM)
 Current Bellyache Bush distribution (taken from Weed Mgmt Plan for Bellyache Bush, NTG)
Hand pulled plants can stay alive for months and still flower and seed, so stems should be snapped.

Parkinsonia threatens the agricultural and environmental values of over three-quarters of the Australian mainland. It can form dense, impenetrable thickets, sometimes several kilometres across, restricting mustering and access to water.

 Parkinsonia leaves (NT Dept LRM)
We also found more Rat’s tail grass at Mt Bundy, and a second landholder said it was also on his property. See a recent story on rat’s tail here.

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