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Published: 2016-09-29 00:00:00

Waikato Regional Council has partnered with Thames-Coromandel District Council and Forest & Bird to release 400 small beetles to combat a big pest weed problem in New Zealand’s oldest arboretum.

The beetles have been specially bred by Landcare Research to tackle tradescantia – also known as wandering willie – in the William Hall Arboretum and Walk at Thames.

Over the past two days the beetles have been released by the regional council’s pest plant officer Benson Lockhart. He was joined by staff from Thames-Coromandel District Council and Forest & Bird, as well as community volunteers.

“We’ve released three different types of beetle, with each one attacking different parts of the plant – the leaf, stem and tip,” said Mr Lockhart. “These beetles have got a big job ahead of them, because tradescantia is thick throughout the arboretum.”

Landcare Research supplied 200 tradescantia tip beetles and 100 tradescantia stem beetles for release. “What’s really exciting is that I was able to harvest about 100 leaf beetles from a site in Hahei where they’ve been doing some great work over recent years to combat the tradescantia problem there,” he said.

Tradescantia smothers the ground, preventing native tree regeneration. The plant is also a real nuisance for home gardeners, as well as causing allergic responses in dogs.

The pest plant is so widespread in New Zealand that manual or chemical control on a large scale is simply not feasible. “That’s where biological control – or biocontrol – comes in. It uses a living organism to control another, and it’s a method that has been used very successfully across New Zealand since the 1920s to safely control a number of different weeds.”

These biocontrol agents do take time to establish, but it’s expected the tradescantia beetles will support pest plant control work already being carried out by TCDC, Forest & Bird and community groups in the arboretum.

Ken Clark, from the Thames branch of Forest & Bird, and his weekly working bee group are one of two regular community groups that have been actively engaged in weed control in the arboretum. He is fully supportive of bringing another tool into play to tackle tradescantia.

At Hahei, where the beetles are well established and working together, tradescantia is noticeably diminished and allowing native karaka seedlings to come back through.

“The beetles have had time to get established at Hahei and it’s awesome to see some good results starting to show. We’re hoping to see the same here at the arboretum,” said Mr Lockhart.

Landcare Research undertake rigorous testing to ensure biocontrol agents are host specific in New Zealand conditions. The tradescantia beetles have been approved since 2011.

Photo: Waikato Regional Council’s Whitianga-based pest plant officer Benson Lockhart releasing small beetles helping to tackle a big problem.