Weed control for Lake Benmore set for this weekend

Land Information New Zealand (LINZ) intends to conduct follow-up control of the aquatic weed pest Lagarosiphon in Lake Benmore, using the herbicide "Aquagel", as early as tomorrow.

Previous attempts to control Lagarosiphon were thwarted by the recent bad weather during February. Spraying is weather-dependent, but it is likely that ground-based spot spraying will be undertaken before 31st March, and aerial spraying will occur between 6th and 9th March 2004, dependent on weather and lake conditions.

Lagarosiphon sites in the Kawarau and Dunstan Arms of Lake Dunstan are also programmed to be treated by aerial spraying of "Aquagel" later this month, again dependent on weather and lake conditions. Lagarosiphon infestations in the Clutha Arm of Lake Dunstan were sprayed in mid-November 2003, with successful results. 

There will be radio advertisements, warning signs, a free-call number (0508 244746) and notification on LINZ's website at www.linz.govt.nz.  Spraying will not take place during Otago Anniversary weekend or the Easter Holidays.

Lagarosiphon was discovered in the Ahuriri Arm of Lake Benmore 12 months ago. Preliminary control efforts in Lake Benmore began in March 2003 using Aquagel.   This treatment was very successful, but Lagarosiphon root material is not killed by diquat, which is a contact herbicide only.  As a result, the weed will re-establish in some areas and continue to spread if spraying is not maintained.  At present there is no other herbicide available for the treatment of aquatic weeds.

Consequently, LINZ applied for resource consent to spray the weed with Aquagel to maintain a level of control over the weed.  A five year resource consent was granted in December 2003 to spray Lagarosiphon in the Waitaki Lakes and connecting waterways with Aquagel.  Aquagel has been used successfully for this purpose in Lake Dunstan, where it is a 'permitted activity', since Spring 2001. 

LINZ administers a number of lakes in the North and South Islands. LINZ Manager, Crown Property, Paul Jackson says the public has an important role to play in bringing issues to LINZ's attention.

"LINZ is actively managing the lakes with our contractors. Other agencies such as Fish and Game and regional councils are also involved. If the public notice anything, particularly weed in areas where it has not previously been, they need to tell us. The lakes cover huge areas and any information on new sites can be acted upon quickly."

For further information please contact:

Paul Jackson
Manager, Crown Property
Land Information New Zealand  
PO Box 5501
WELLINGTON
PH: 04 460 0158
FAX: 04 460 0590
EMAIL: pjackson@linz.govt.nz

LINZ media liaison:

Michael Mead 
Senior Communications Adviser       
Land Information New Zealand   
PO Box 5501
WELLINGTON
PH: (04) 498 3516
FAX: (04) 472 1864
EMAIL: mmead@linz.govt.nz

Notes for editors

Lagarosiphon facts

• Lagarosiphon major (Hydrocharitaceae) is an oxygen weed that has become established in many New Zealand waterways. It prefers clean, clear water, where it forms dense stands that out compete native vegetation and can cause problems for both recreational users and native species.
   
• Diquat is the only herbicide registered for aquatic use in New Zealand. The usual way of applying diquat to control aquatic weeds is as a gel. This method has the advantage that not only is there is no "spray drift", but the gel containing the herbicide sinks through temperature gradients in the weed bed and, therefore, provides better control than can be achieved using diquat in an aqueous form. 
   
• Studies undertaken by NIWA (The Impacts of Weed Beds and Diquat Spraying of the Freshwater Mussel, Hydrilla menziesi. Wells & Clayton, 1996), have found no effects on the freshwater mussel. Further work by NIWA (HortResearch, 2001, Pesticide Residue Report No. 1861) has found no bio-accumulation of diquat in the sediment at sites which have been regularly treated. The discharge of diquat in gel form is a permitted activity in Otago Region. It has also been used in the Rotorua Lakes for the last 25 years.

More Information:

More information on LINZ's weed programme is available on the LINZ web site.