Rubber Bush Chemical Control Trials Show Mixed Results

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The exotic weedy shrub rubber bush (Calotropis procera) poses increasing risk to valuable grazing land across northern Australia.

Declared as a Northern Territory Class B (growth and spread to be controlled) and Class C (not to be introduced into the NT) weed, rubber bush is toxic to humans and stock, can form dense thickets on disturbed and degraded soils,  competes with native pastures, smothers native plants, inhibits access to watering points and restricts mustering.

To better understand rubber bush Meat and Livestock Australia approved and funded a collaborative research project involving pastoralists, Charles Darwin University and the Queensland and Northern Territory Governments.

The research project studied the invasiveness, biology, ecology, distribution and control of rubber bush in Northern Australia.

As part of this research project the NTG Weed Management Branch undertook on ground chemical trials on the Barkly Tablelands, Northern Territory.

These trials replicated the trials applied in Queensland and produced similar results, but some varied results particularly with the soil applied chemical, Tebuthiuron, as DENR District Weeds Officer Naomi Cassilles Southgate will explain at this week’s Territory Natural Resource Management Conference in Darwin.

“Land managers such as pastoralists and rangers regularly raise their concerns of rubber bush spread, how large infestations are and how hard it is to control, often finding they treat rubber bush and it hasn’t been successful or it has re-shot from the base,” Ms Cassilles Southgate said.

“Initial on ground chemical trials evaluated chemical control methods in Queensland, with several herbicide options using foliar, basal bark and cut stump techniques, with ground or aerial applications of residual herbicides.

“To test the relevance and effectiveness of these treatments under pastoral conditions in the Barkly Tablelands a trial was established in May 2014.

“Ground application of the residual herbicide Tebuthiuron was one of the treatments included and showed excellent results in Queensland but poor results in the Barkly warranting further investigation, as this application method is easy to apply being a pellet form and has a residual effect preventing recruitment.

“A technique we often recommend to land managers that showed excellent results from the trials in Queensland and the Barkly is the basal bark technique, including:

  • One application rate at a mix of one litre Triclopyr/picloram / 60 litres of diesel, applied 30-40cm up the trunk, ensuring to soak the base of the plant until point of run-off
  • A second application rate of one litre Triclopy/picloram / 10 litres of diesel only 5cm up the trunk, ensuring to soak the base of the plant until point of run-off

Go to www.nt.gov.au/environment/weeds for more information about declared weeds in the Northern Territory.

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