Noxious weed easy to kill

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The noxious aquatic weed lagarosiphon is “really easy to kill” with aerial spraying, it just needs someone to spend money on getting it done, Guardians of Lake Dunstan member John Wilson says.

It did not matter which of the parties involved, the Otago Regional Council (ORC), Contact Energy or Land Information New Zealand (Linz), carried out control work in Lake Dunstan, as long as someone did, he said.

“We just want someone to take responsibility.”

Linz had last year sprayed part of the shoreline and the results had been great, with the weed completely eradicated where it had been sprayed, he said.

“They have sprayed the first 8m so why not do the rest?

“We will lose Cromwell if nothing is done. I have seen it in France.”

Mr Wilson said on a trip to France he saw areas where waterways were completely choked by lagarosiphon. The smell when it was rotting was terrible and those areas had now been cleaned up, he said.

“It breaks off into rafts and rots and smells.”

The weed was dangerous to boat users, swimmers and water skiers.

“End up among it and you could be in trouble.”

It also made fishing difficult and children found it hard to cast out past the shore, he said.

It had taken 10 to 15 years for lagarosiphon to become a real problem in Lake Dunstan, he said.

“Its a bit late to eradicate it . . . but we need a strong control programme. It’s a simple job done by helicopter.”

The ORC website says lagarosiphon “chokes waterways, and can spoil your fun on Otago’s lakes and rivers”.

It was sold as an aquarium or ornamental pond plant and is thought to have been accidentally introduced to our waterways through disposal into drains and ponds.

Lagarosiphon spread rapidly, displacing native plants, and made swimming and other water-based leisure activities less pleasant. It could grow up to 4m in length, choking and blocking lakes and rivers, the website said.

Linz is the owner of the lake beds in the Southern Lakes and is the lead agency responsible for the associated weed and pest-control programmes.

ORC environmental monitoring and operations director Scott MacLean told The News last week the ORC was a member of the respective management groups for the Southern Lakes and was pleased to support Linz and the other agencies and community groups involved in the management of lagarosiphon in Otago.

“As part of our contribution to the . . . control programme, we spend about $50,000 a year in the management of lagarosiphon. Much of this is spent in Lake Wanaka and funds monitoring and surveillance activities.”

The ORC’s goals for Lake Dunstan were to protect other water bodies from lagarosiphon transfer, minimise weed impacts on lake users within high-value areas, involve the community in decision-making and improve the cost-effectiveness and efficacy of control works, Mr MacLean said.