Arsenal upped in lake weed war

IAIN McGREGOR/Waikato Times

WEEDS BE GONE: A Hanmer Springs-based helicopter sprays diquat on Lake Karapiro yesterday.

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The war on the invasive weed hornwort continued on Lake Karapiro yesterday afternoon with a new weapon added to the arsenal.

Land Information New Zealand (Linz) used a Hanmer Springs-based contractor to apply diquat, a herbicide gel, by helicopter to the lake.

The free-floating weed, which is easily displaced by wind or wave action, has become an increasing irritant for recreational users and particularly the rowing fraternity as they prepare for the 2010 World Rowing Championships.

The gel is being used in addition to an Australian-built $320,000 lake weed harvesting machine bought by Karapiro Rowing Incorporated last year.

A Linz spokesperson said the weed-harvesting boat was still being used but the herbicide gel, which kills the whole plant, was a faster and more effective way of managing hornwort.

Diquat was first used on the lake in May, when about 50ha was treated.

Yesterday another 50ha of the lake was covered.

Diquat is mainly applied to Karapiro's shoreline because the invasive hornwort, which needs sunlight to grow, is concentrated in shallow areas of the lake.

Linz spokesman Paul Jackson said the water should not be drunk or used for irrigation for 24 hours after application. Environment Waikato set strict rules for the application of the gel.

- © Fairfax NZ News