Setting bugs against a pest weed

Our Council has worked with Waikato Regional 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. For more on the arboretum go to www.tcdc.govt.nz/thamesarboretum.

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 our 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 our Council, 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.

William Hall Arboretum and Walk

John William Hall was a Thames chemist who began planting his three-acre property in Parawai in 1872 - initially to control erosion.

He had become alarmed at the effect rainfall had on the area's deforested hillsides - the trees having been cut to make pit props for the gold mines. However, he also planted for habitat provision and research. Mr Hall was an amateur naturalist in the best tradition of the Victorian era.

About 180 of his plantings survive today and form an eclectic collection of plants from around the world. Some of the plantings were of New Zealand natives and he recorded their progress fastidiously. Hall's Totara is named in his honour.

A path through the arboretum takes walkers past the plants Mr Hall planted all those years ago.

The arboretum has four entrances: Brunton Crescent, Korokoro Crescent, Currie St and Mount Sea Road. A small car park is at the top of Mount Sea Rd.

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